

مجله مكانيك سيالات كاربردي
Journal Of Applied Fluid Mechanics
ISSN 17353572
دوماهنامه داراي رتبه علمي  پژوهشي (علوم پايه) به زبان انگليسي
سال دهم، شماره 6، 2017




 Numerical, Experimental and Analytical Studies on Fluid Flow through a Marsh Funnel S. Sadrizadeh* , A. N. Ghaffar , A. Halilovicc , U. Hokansson Pages 15011507 Abstract Full Text [PDF 264KB]   This paper presents the application of computational fluid dynamics technique in civil and underground industries to evaluate fluid behaviour in a Marsh funnel. The numerical approach، based on computational fluid dynamics، simulated an incompressible twophase Newtonian flow by means of the VolumeofFluid method. A complementary analytical proposed which provided a quick، fieldready method to assess the fluid field in the Marsh funnel. A supplemental experimental effort evaluated the results obtained from both the analytical calculation and numerical simulation. Results showed that the application of computational fluid dynamics technique gives the desired results in studying fluid flows in civil and underground industries. Proposed analytical solution is also capable of accurately predicting the fluid flow and thus can complement the experimental and numerical approaches. Further، the proposed analytical approach can be an alternative method for faster evaluation of fluid، although it needs to be calibrated with either the numerical or the experimental studies.
Keywords: Multiphase flow; Marsh funnel; CFD; Analytical solution; Experimental approach; Fluid flow simulation; Discharge coefficient; Cementbased grout
  
 Experimental Evaluation of the Critical Flutter Speed on Wings of Different Aspect Ratio J. Bertrand , H. Fellouah* , K. Alsaif Pages 15091514 Abstract Full Text [PDF 307KB]   In this work، wind tunnel experiments were conducted to evaluate the critical flutter speed of wings for three pertinent flight parameters (i) the aspect ratio (AR)، (ii) the angle of attack (AoA)، and (iii) the aircraft propeller excitation. Six symmetrical wings (NACA0012 design)، of fixed chord length of 80 mm and varied AR from 8.75 to 15، were used for this purpose. These wings were mounted horizontally in the wind tunnel as fixedfree condition. The airflow speed is increased slowly until the wing flutters. The results show that the critical flutter speed decreases when the AR increases. For higher AR، the effect of the AoA on the flutter speed is minimal. However، for low AR، the AoA is vital in delaying the flutter instability of the wing. This critical speed spans low to moderate Reynolds numbers based on the wing chord length (Rec =7×1042×105) which corresponds to the speed range of High Altitude and Long Endurance (HALE) aircraft. In contrast، for a propeller excitation outside the resonance region of the wing، its effect of the on flutter characteristics is not noticeable.
Keywords: Aeroelasticity; Flutter; Wings; Aspect ratio; Angle of attack; Wind tunnel measurements
  
 Oscillations of Water Levels in Vertical SemiImmersed Tubes: Analytical Solutions and Experimental Verification H. E. Schulz * , D. Z. Zhu Pages 15151525 Abstract Full Text [PDF 451KB]   Experimental results for water level oscillations in vertical tubes، together with a theoretical solution for the flow in such tubes considering local and distributed energy losses، are presented and compared. The experimental data were obtained in small scale experiments، allowing adequately controlling the oscillations. The governing equation for the oscillations was obtained by applying the conservation laws of mass، momentum and energy for fluids. It is a second order nonlinear differential equation which was reduced to a first order differential Bernoulli equation. The obtained solution is composed by two different equations، one for the upwards motion and the other for the downwards motion، which together reproduce the oscillatory damped behavior of such flows. Numerical solutions of the differential equation were also checked. The experimental data and the theoretical and numerical results showed a good agreement between measured and calculated values of velocity and surface level for the first periods of oscillation.
Keywords: Water level fluctuations; Damped fluctuations; Oscillation suppressing devices; Applied nonlinear differential equations
  
 NewConcept Gas Turbine Burner Simulation in Moderate Intense LowOxygen Combustion Regime A. Di Nardo * , G. Calchetti Pages 15271536 Abstract Full Text [PDF 1059KB]   In a trappedvortex combustor (TVC) flame stabilization is achieved through intense internal exhaust gases recirculation، which is promoted by the adoption of cavities. Thanks to its peculiar features، a trappedvortex burner produces low pressure drop and emissions and it is characterized by extended blowout limits. The strong mixing of fresh reactants with flue gases due to internal recirculation represents the basis for the establishment of a distributed MILD، i.e. "Moderate Intense LowOxygen Dilution Combustion" regime، which is characterized by reduced temperature peaks، volumetric distributed reactions، low NOx emissions and no thermoacoustic instabilities. Aim of the work is to study the possibility to obtain a MILD regime in our available trappedvortex device، taking the advantage of the combined effect of TVC strong internal exhaust gases recirculation and of oxycombustion external exhaust recirculation، attaining the benefits of CO2 capture at the same time. To this end a series of computational fluid dynamics simulations were conducted on our TVC device، in order to understand the influence on combustion of the main operating parameters، such as the equivalence ratio، the level of dilution، the injection temperature، the velocity، etc.. A preheating temperature and a range of oxygen concentrations that at the same time complies with a distributed reactions regime and an efficient combustion were identified for the premixed and nonpremixed operating modes.
Keywords: Trappedvortex burner; MILD combustion
  
 A Computational Study on the Performance Improvement of LowSpeed Axial Flow Fans with Microplates D. Luo , D. Huang * , X. Sun , X. Chen , Z. Zheng Pages 15371546 Abstract Full Text [PDF 430KB]   This paper proposes the use of microplates as a new flow control device to suppress boundary layer separation on blades and thus improve the aerodynamic performance of a lowspeed axial flow fan. A computational study is performed by means of computational fluid dynamics (CFD) simulations. Numerical investigations are carried out based on Reynoldsaveraged NavierStokes (RANS) method. The shear stress transport (SST) turbulence model and highquality computational grids are adopted for CFD simulations. An exhaustive comparison of the fans with and without control has been conducted in terms of characteristic curves، streamlines and pressure distributions. The purpose of this work is to better understand the underlying flow control mechanisms of microplates. It is found that the total efficiency is slightly lowered when the controlled fan operates at the design flow rate. However، as the flow rate changes، the total efficiency of the controlled fan varies more gently than the original fan without control. Traced streamlines show that flow separation on blade surfaces is effectively controlled and radial flow migration on the suction surface is evidently diminished. Numerical results indicate that microplates significantly alleviate fan stall and have considerable beneficial effects on fan performance.
Keywords: Axial flow fan; Flow control; Microplate; Computational fluid dynamics (CFD)
  
 Performance Evaluation of a Trapezoidal Microchannel Heat Sink with Various Entry/Exit Configurations Utilizing Variable Properties H. Khorasanizadeh * , M. Sepehnia Pages 15471559 Abstract Full Text [PDF 921KB]   Most of numerical studies on microchannel heat sinks (MCHS) performed up to now are for a twodimensional domain using constant properties of the coolant and solid part. In this study، laminar fluid flow and heat transfer of variable properties water in a trapezoidal MCHS، consisted of five trapezoidal microchannels، are studied. The three dimensional solution domains include both the flow field and the complete MCHS silicon made solid parts with variable conductivity. Four entry/exit configurations and three pressure drops of 5، 10 and 15 kPa are assumed. The results indicate that the Atype heat sink، for which the entry and exit are placed horizontally at the center of the north and the south walls، has a better heat transfer performance، smaller thermal resistance and provides more uniform solid temperature distribution. For pressure drop of 15 kPa، temperaturedependent properties of water increases the heat transfer between 2.73% and 3.33%، decreases the thermal resistance between 3.46% and 5.55 % and decreases the ratio of difference between the maximum and minimum substrate temperatures to the heat flux، θ، between 3.42% and 11.15%. Also by assuming temperaturedependent conductivity of silicon، the heat transfer increases between 0.75% and 2.58%، the thermal resistance decreases between 1.15% and 4.97 % and θ decreases between 2.41% and 6.49%.
Keywords: Trapezoidal microchannel; Entryexit configurations; Temperaturedependent properties; Thermal resistance; Heat transfer
  
 A Novel Alternating Cell Directions Implicit Method for the Solution of Incompressible Navier Stokes Equations on Unstructured Grids O. Bas , A. R. Cete * , S. Mengi , I. H. Tuncer , U. Kaynak Pages 15611570 Abstract Full Text [PDF 271KB]   In this paper، A Novel Alternating Cell Direction Implicit Method (ACDI) is researched which allows implementation of fast line implicit methods on quadrilateral unstructured meshes. In ACDI method، designated alternating cell directions are taken along a series of contiguous cells within the unstructured grid domain and used as implicit lines similar to Line Gauss Seidel Method (LGS). ACDI method applied earlier for the solution of potential flows is extended for the solution of the incompressible NavierStokes equations on unstructured grids. The system of equations is solved by using the Symmetric Line GaussSeidel (SGS) method along the alternating cell directions. Laminar flow fields over a single element NACA0008 airfoil are computed by using structured and unstructured quadrilateral grids، and inviscid Euler flow solutions are given for the NACA23012b multielement airfoil. The predictive capability of the method is validated against the data taken from the experimental or the other numerical studies and the efficiency of the ACDI method is compared with the implicit Point Gauss Seidel (PGS) method. In the selected validation cases، the results show that a reduction in total computation between 18% and 23% is achieved by the ACDI method over the PGS. In general، the results show that the ACDI method is a fast، efficient، robust and versatile method that can handle complicated unstructured grid cases with equal ease as with the structured grids.
Keywords: Alternating cell directions implicit method; ACDI; UMUSCL; Artificial compressibility; Incompressible NS solver
  
 Study of Inertia and Compressibility Effects on the Density Wave Oscillations of TwoPhase Boiling Flows in Parallel Channels Y. Bakhshan* , S. Kazemi , S. Niazi , P. Adibi Pages 15711581 Abstract Full Text [PDF 340KB]   In this research، a theoretical model is presented to investigate the density wave oscillations (DWOs)، in two horizontal parallel channels with lumped parameter model based on two phase homogeneous hypothesis. The parallel channel is composed of the entrance section، heating section and outlet section and the model consists of the boiling channel model، pressure drop model، parallel channel model، constructive model and inertia and compressibility effects، while subcooled boiling effect is neglected and the governing equations are solved by Gear method. The model is validated with experimental data of a single channel flow instability experiment. Then the flow instability in twin channel system is studied under different conditions. This model can analyze the effects of external parameters، such as fluid inertia and compressible gases on the stability margins of density wave oscillations. The results show that، the fluid inertia and compressible gases can significantly change the stability margins of two parallel channels; in fact، the stability behavior of two parallel channel system improves with increasing the inlet inertia and outlet compressibility but، increasing the outlet inertia and inlet compressibility have negative effects the system stability.
Keywords: Density wave oscillations; Parallel channels; Fluid inertia effects; Compressibility effects
  
 Influence of Smooth Constriction on Microstructure Evolution during Fluid Flow through a Tube V. Ferrer , R. MilMartί, , nez , J. Ortega , R. O. Vargas * Pages 15831591 Abstract Full Text [PDF 938KB]   A numerical solution for axissymmetrical fluid flow through a smooth constriction using the alternating direction implicit finite volume method and the fractionalstepmethod is presented. The wall is modelled with a smooth contraction mapped by a sinusoidal function and the flow is supposed to be axissymmetric. A pressure boundary condition is set at the inlet and the resulting pressure gradient field drives fluid flow which is always in laminar regime. This study presents results for a nonNewtonian fluid using the Ostwaldde Waele constitutive model. Moreover، a transient network representing three different microstructures، immersed in the fluid، is evolved by viscous dissipation and an isothermal process is considered. The time dependent evolution of the transient network is represented by a set of kinetic equations with their respective forward and reversed constants. The numerical predictions show that، at a fixed Reynolds number، the viscous dissipation and the grade of structure restoration or breakage is influenced by constriction severity due to the energy generated during fluid flow. A 50% reduction in transversal section generates secondary flow downstream and vortex shedding، whereas a 10% and 25% constrictions presents a thin boundary layer and no secondary flow near the constricted wall.
Keywords: Generalized Newtonian fluid; Transient network; Finite volume method; Fractionalstep method
  
 Analyzing Free Vibration of a Cantilever Microbeam Submerged in Fluid with Free Boundary Approach K. Ivaz* , D. Abdollahi , R. Shabani Pages 15931603 Abstract Full Text [PDF 1249KB]   This paper aims to present a detailed analysis of the free vibration of a cantilever microbeam submerged in an incompressible and frictionless ﬂuid cavity with free boundary condition approach. In other words، in addition to the kinematic compatibility on the boundary between microbeam and its surrounding ﬂuid، equations of the potential functions are modeled assuming the free boundaries. Galerkin’s method is used for simulations. The results of the proposed model are validated by comparing with the early analytical and numerical studies of pertinent literature. Finally، it is inferred that by involving the free boundary conditions، which is closer to the physical reality، the natural frequencies of the system have instability، especially in higher modes. In addition، the values obtained for natural frequencies are smaller than what were calculated by ﬁxed bounary approach.
Keywords: Vibration; Free boundary equation; Added mass; Microbeam
  
 Numerical Studies on Thrust Augmentation in High Area Ratio Rocket Nozzles by Secondary Injection S. Shyji * , M. Deepu , N. A. Kumar , T. Jayachandran Pages 16051614 Abstract Full Text [PDF 707KB]   Single stage to orbit propulsion devices are being developed as part of low cost access to space endeavors. Sea level operation of high area ratio rocket nozzle used in rocket engines leads to an overexpanded flow condition resulting in high side loads. Secondary injection of propellants in high area ratio nozzle is an attractive option to overcome the inefficiency of operation of such nozzles in sea level conditions in addition to the augmentation of thrust. A numerical study on thrust augmentation in high area ratio nozzle by secondary injection of propellants is presented here. The turbulent compressible reacting flow in rocket nozzle with auxiliary injection is simulated using conservation equations for chemical species based on finite rate chemistry model and compressible NavierStokes equations with AUSM+up upwind scheme based unstuctured finite volume solver. An optimized eight step، six species reduced H2O2finite chemistry reaction model is used to model the supersonic combustion. The indigenously developed solver has an efficient rescaling algorithm to alleviate the effect of stiffness in conventional explicit algorithm for simultaneous solution of reacting flow. The code is validated using the wall pressure and hydrogen concentration values reported for the similar high area ratio rocket nozzle. Accurate prediction of nozzle performance is possible with present turbulent reacting flow simulation as it take care of all losses in nozzle flow. Extensive computations have been performed for the performance estimation of high area ratio rocket nozzle for various prospective auxiliary injection options.
Keywords: Rocket nozzles; Thrust augmentation; Turbulent reacting flows; AUSM+up scheme; Finite volume method
  
 Convective Heat Transfer Enhancement using Slot Jet Impingement on a Detached Rib Surface A. K. Shukla , A. Dewan * Pages 16151627 Abstract Full Text [PDF 310KB]   This paper presents results of a computational study to investigate the suitability of various RANS based turbulence models for slot jet impingement over flat and detached ribbed surfaces. The computed results are compared with the reported experimental data. It is observed that some turbulence models predict the experimental data with good trends، e.g.، secondary peak in Nusselt number and distribution of normalized streamwise velocity. The standard kω and SST kω models predict heat transfer more accurately compared to that by other models with prediction of a secondary peak in Nusselt number. Distributions of turbulent kinetic energy، streamwise velocity and normal velocity are also analyzed to understand heat transfer behavior with flat and detached rib surfaces. Various parameters are considered to obtain a good understanding of heat transfer enhancement with jet impingement on a surface fitted with detached ribs. Further the effects of rib to plate clearance، position of first rib and Reynolds number on heat transfer characteristics are also investigated. It was observed that flow and heat transfer features are significantly affected by the placement of ribs on the impingement surface. Increasing the rib clearance، position of first rib in the streamwise direction and Reynolds number have favorable effects on heat transfer. The detached rib configuration offered augmentation in Nusselt number compared to the attached rib arrangement (i.e.، with no clearance between the rib and impingement surface). Comparisons of stagnation point and average Nusselt numbers are also presented to understand heat transfer enhancement for flat and ribbed surfaces.
Keywords: Slot jet impingement; Heat transfer; Ribs; Turbulence modelling; Nusselt number; RANS
  
 Behaviour of Mean Velocity in the Turbulent Axisymmetric Outer Near Wake T. Yane * , N. Subaschandar Pages 16291637 Abstract Full Text [PDF 139KB]   An asymptotic study of the outer near wake of a long slender body of revolution is carried out. The long slender body is a cylinder which is kept parallel to the flow and takes the shape of a simplified geometry such as that of an underwater vehicle، a rocket or hull form of a ship model. The wake flow is axisymmetric and the analysis has been carried out without any assumption on the eddy viscosity but utilizing the general behaviour of turbulent shear stress in the near wake. The governing equations are solved with appropriate boundary conditions. Similarity analysis for the mean velocity characteristics is carried out which shows the existence of a logarithmic region in the normal direction in the overlap region between the outer near wake and the inner near wake. Also shown is the exponential decay of the mean velocity defect as freestream velocity is reached. Validation of the results of the analysis is done using available experimental data.
Keywords: Axisymmetric; Outer near wake; Boundary layer; Turbulence
  
 Numerical Simulation of MHD Fluid Flow inside Constricted Channels using Lattice Boltzmann Method M. Jamali Ghahderijani , M. Esmaeili , M. Afrand * , A. Karimipour Pages 16391648 Abstract Full Text [PDF 342KB]   In this study، the electrically conducting fluid flow inside a channel with local symmetric constrictions، in the presence of a uniform transverse magnetic field is investigated using Lattice Boltzmann Method (LBM). To simulate Magnetohydrodynamics (MHD) flow، the extended model of D2Q9 for MHD has been used. In this model، the magnetic induction equation is solved in a similar manner to hydrodynamic flow field which is easy for programming. This extended model has a capability of simultaneously solving both magnetic and hydrodynamic fields; so that، it is possible to simulate MHD flow for various magnetic Reynolds number (Rem). Moreover، the effects of Rem on the flow characteristics are investigated. It is observed that، an increase in Rem، while keeping the Hartman number (Ha) constant، can control the separation zone; furthermore، comparing to increasing Ha، it doesn't result in a significant pressure drop along the channel.
Keywords: Lattice Boltzmann method; Magnetohydrodynamics; Constrictions; Magnetic Reynolds number; Hartmann number
  
 Characteristics of CNG Bubbles in Diesel Flow under the Influence of the Magnetic Field H. A. Abdul Wahhab , A. R. A. Aziz * , H. Al Kayiem , M. S. Nasif Pages 16491655 Abstract Full Text [PDF 675KB]   This paper conducts an analytic study of the hydrodynamics of a small CNG bubbles in laminar horizontal Diesel flow under the influence of the magnetic field. Investigation based on experiments was carried out to identify the effects caused by varying the magnetic field intensity on the trajectory، the formation of bubbles and their shape and velocity. Different images at different positions were captured through a high speed camera، image processing technique and downstream from the CNG bubbles injection point delivered information on bubble velocity، bubbles size، spatial location and gas area fraction as a function of changing magnetic field intensity. The outcomes confirmed that CNG bubbles under magnetic field grow up vertically to have a bigger elliptical shape in the Diesel phase with the twofold of diameter. Also، it has been noted that the CNG bubbles velocity decreased as the magnetic field strengthened.
Keywords: Fuel technology; Liquidgas fuel mixer; Magnetic field; Two phase hydromagnetic flow
  
 Entropy Production Analysis for SCharacteristics of a Pump Turbine R. Z. Gong , N. M. Qi , H. J. Wang* , A. L. Chen , D. Q. Qin Pages 16571668 Abstract Full Text [PDF 644KB]   Due to the Sshape characteristics and the complicated flow in pump turbine، there may be serious instability when the pumpstorage power plant starts. In order to conduct further study on the energy dissipation in hydraulic turbine، three dimensional incompressible steady state simulations were applied using SST kω turbulence model in this paper. It can be seen that the simulation results are consistent with experimental results well by the comparison of characteristic curves، and further analyses were made based on the entropy production theory. It is shown that the entropy production of spiral casing accounts for the minimum proportion in all components. The entropy production of cascades and runner differs a lot at different guide vane openings، and it features “S” characteristics with the increase of discharge. Then، the analysis of entropy production distribution on runner، blade cascades and draft tube was carried out at the 10mm guide vane opening. It was found that the losses in guide vane space is much higher than that of stay vane space and the losses are mainly in the tail area of stay vanes and vaneless space. The losses mainly occurs in the leading edges and the trailing edges of blades. The largest losses mainly lie at the wall of straight cone near the inlet in draft tube. The losses at the inner surface of elbow are also very high. The results indicate that the method based on the entropy production theory is very helpful to analyze and locate the losses in hydraulic turbine.
Keywords: Hydraulic turbine; Sshape characteristics; Entropy production; Energy losses
  
 Flow and Solute Transport through a Single Fracture during the Biodegradation of Residual Toluene Y. Tan* , B. Lu , T. Wu , S. Wu , H. Sha , P. Zhou Pages 16691677 Abstract Full Text [PDF 485KB]   A series of bench scale experiments were performed to assess the effects of biofilm and bioenhanced toluene dissolution on flow and solute transport through a rough fracture. The fracture was cast from a real shale rock fracture. Sterilized artificial groundwater was used as the nutrition source to support the growth of microorganisms which were obtained from local groundwater. Hydraulic and tracer tests were carried out before and after the injection of toluene، and during the toluene biodegradation as well. The normalized hydraulic conductivity decreased sigmoidally during the experiment، and reached 0.02 at the end of the experiment. Biofilm growth was the main cause for hydraulic conductivity reduction after the injection of liquid toluene. The presence of separate phase toluene extended the tracer tailing compared to tracer tests without toluene. The longitudinal dispersion coefficient DL was proportional to the 1.5th power of the mean velocity in the rough fracture with or without residual toluene. Though a biofilm developed in the fracture during biotreatment، the effect of secondary biofilmassociated porosity on solute transport in the fracture had negligible effect on tracer transport due to its small thickness. It is also found that DL decrease exponentially with Pe reduction during the biotreatment.
Keywords: Fracture; Flow; Solute transport; Toluene; Biofilm
  
 Experimental Investigation of Tip Vortex Meandering in the Near Wake of a HorizontalAxis Wind Turbine A. W. Dahmouni * , M. M. Oueslati , S. Ben Nasrallah Pages 16791688 Abstract Full Text [PDF 985KB]   The aerodynamic optimization of horizontal axis wind turbine has became one of the most important challenge in the renewable energy field. Over the past few years، many researchers have drawn more attention to the physical processes of the wind energy conversion and precisely the identification of the main causes of energy losses. This paper presents an experimental investigation of near wake dynamics for a model horizontal axis wind turbine in a wind tunnel. The coherent structures downstream of the rotor were studied for different tip speed ratios using the Particle Image Velocimetry (PIV) technique. The influence of the tip vortex meandering was discussed and analyzed using the Proper Orthogonal Decomposition (POD) method. The highenergy modes show that radial meandering is the most energetic source of perturbation in each tip vortex subregion. The energy fraction of these modes increase gradually during the development of the helical tip vortex filament، which confirm the growth of vortex wandering amplitude in the near wake.
Keywords: Wind turbine; Near wake; Tip vortex; Meandering; POD
  
 Aerodynamics of Flapping Wings for Vertical Takeoff G. C. Vishnu Kumar * , D. A. Shah Pages 16891697 Abstract Full Text [PDF 827KB]   The present study is based on analysing a flapping based locomotion in vertical direction which is inspired from jelly fish in vertical locomotion. A numerical investigation is performed to analyse the aerodynamic performance in terms of two dimensional flat plates under flapping conditions with the fluid at rest. The model considered is an umbrella structure prototype which has vertical plates placed at certain intermittent distance from each other with their leading edges hinged. The dynamic effect of 2D plates are analysed by varying the chord length of flapper for a range of amplitude and frequency to study the interference effects of flappers in close proximity. It is found that a suitable chord length and intermittent distance is required for improving the aerodynamic characteristics. It is envisaged that the results obtained in this study will lead to better understanding of the dynamics of flapping based locomotion which are useful for developing hovering kinematics in surveillance and reconnaissance.
Keywords: Flapping; Flat plates; Numerical simulation; Vortex structure
  
 Numerical Study on FluidStructure Interaction in a PatientSpecific Abdominal Aortic Aneurysm for Evaluating Wall Heterogeneity and Material Model Effects on its Rupture Y. Mesri , H. Niazmand * , A. Deyranlou Pages 16991709 Abstract Full Text [PDF 583KB]   Abdominal Aortic Aneurysm (AAA) is one of the main cardiovascular diseases، which threats human’s health while it appears، develops and in crucial cases ruptures and leads to hemorrhage. In the current work، we aim to investigate numerically the transient blood flow in a patientspecific AAA model، while effects of wall compliance is considered by employing the fluidstructure interaction method. The AAA model is reconstructed from acquired CT angiographic data of a patient diagnosed with AAA and an intraluminal thrombus (ILT). For the comparison purposes two different material models، i.e. isotropic and anisotropic are considered. Additionally، to have a better estimation، wall thickness variability is compared with simpler uniform wall thickness model. In this study NavierStokes equations along with elastodynamics equation are coupled through Arbitrary LagrangianEulerian formulation method and solved numerically. Findings demonstrate that the isotropic material model with uniform wall thickness significantly underestimates wall stresses as compared to the anisotropic material model with variable wall thickness. Indeed، results emphasize that considering vessel wall as an anisotropic، heterogeneous (variable thickness) structure estimates much higher wall stresses comparing with isotropic، uniform thickness model. Therefore، given realistic vessel wall structure and the fact that the anisotropic، variable wall thickness model predicts higher wall stresses، it could be a more reliable model to give an accurate estimation to physicians to diagnose the stage of a disease and choosing an appropriate therapeutic procedure.
Keywords: Abdominal aortic aneurysm; Fluidstructure interaction; Material model; Wall thickness
  
 Heat and Mass Transfer Enhancement in Absorption of Vapor in Laminar Liquid Film by Adding NanoParticles S. Armou* , R. Mir , Y. El Hammami , K. ZineDine , M. El Hattab Pages 17111720 Abstract Full Text [PDF 404KB]   In this paper، a numerical study was performed. The effect of nanoparticles on the absorption of vapor into a liquid film of lithium bromide aqueous solution flowing down over a cooled vertical channel is examined. The present model uses the numerical finite volume method to solve the parabolic governing equations for twodimensional and laminar flow. In this model، the cooling water flows countercurrent to a solution of concentrated lithium bromide mixed with the nanoparticles. The water vapor is then absorbed at the interface of the absorbent film and diffused into the binary nanofluid (waterLiBr+nanoparticles). The numerical results indicate that the mass and heat transfer in binary nanofluids are enhanced more than that in base fluid and the highest absorption mass flux is observed by adding argent (Ag) nanoparticles. The results of the effects of operating conditions show that the effectiveness of the nanofluid becomes higher than that with the base fluid when the Reynolds number and inlet concentration are lower and when the inlet temperature solution and inlet pressure are higher.
Keywords: Heat transfer; Mass transfer; Enhancement; Absorption process; Falling film; WaterLithium bromide; Nanoparticles; Numerical simulation
  
 Tangential Flow Analysis of Giesekus Model in Concentric Annulus with Both Cylinders Rotation M. Jouyandeh , M. Moayed Mohseni * , F. Rashidi Pages 17211728 Abstract Full Text [PDF 448KB]   Giesekus viscoelastic fluid is solved analytically for purely tangential flow in a concentric annulus at laminar and steady state conditions. Flow is created by a relative rotational motion between the cylinders. The analytical expressions for yield dimensionless velocity profile، pressure distribution، (f and Re are Fanning friction factor and Reynolds number) and material functions (viscosity، first and second normal stress difference coefficients) are obtained in cylindrical coordinates. Results show that difference between the values of lower as well as upper critical limits of the velocity ratio (where the minimum velocity happens) with their corresponding Newtonian values increase when mobility factor and Deborah number increase. The results also show that viscometric functions decrease by increasing elasticity because the viscoelastic fluid shows the shear thinning behavior which is strengthened by increasing elasticity. It is found that، for all values، profiles are symmetrical around ( and k are velocity ratio and radius ratio) because no relative motion exists.
Keywords: Giesekus model; Deborah number; Elasticity; Velocity ratio; Material functions
  
 Study of Snow Accumulation on a HighSpeed Train’s Bogies Based on the Discrete Phase Model F. Xie , J. Zhang , G. Gao* , K. He , Y. Zhang , J. Wang , Y. Zhang Pages 17291745 Abstract Full Text [PDF 606KB]   During winters، the highspeed train travels in the northern of China is struck by to the snow، ice and coldness، massive snow accumulating on the bogies. To understand the cause of snow packing on the highspeed train’s bogies clearly، the 3D unsteady Reynoldsaveraged NavierStokes equations with a RNG doubleequations turbulence model and a DPM discrete phase model were used to investigate the flow field carried snow particles in a single highspeed train bogie region and monitor the movement of snow particles. And، the numerical simulation was verified by the wind tunnel test. The results show that when air flows into the region، the airflow will rise and impact on the wheels، brakes، electromotors and other parts of bogie regions. The snow particles will follow the air، while the air direction changes sharply the particles will keep the movement due to the inertia. Afterwards، the snow packs on the bogie. In front of the bogies the streamlines of the air and the particle path lines are basically the same. However، due to the inertia of mass particles، the following characteristics of the snow particles with the air are not obvious in the bogie leeward side. Different structures of the end plates will affect the snow accumulation in the bogie regions.
Keywords: Bogie; Discrete phase; Snow accumulation; Flow characteristics
  
 Measurement and Investigation on the Jet Interface Structure C. Gong* , M. G. Yang , W. D. Jia Pages 17471758 Abstract Full Text [PDF 470KB]   The well understanding of interface structure of liquid jet is the basis of the research of primary breakup. In this paper، the interface structure of liquid jet is captured by using a highspeed photography. The key parameters of interface structure، streamwise wavelength، spanwise wavelength and generation position، are measured based on a power spectral method. The results show that jet interface is featured by a group of periodic structures in the region near the nozzle exit. The position where periodic structure generated fluctuates in a certain region with the variation of time and spanwise position. The spanwise wavelength of these periodic structures is the function of nozzle diameter and the wavelength increase ratio of transition region. Along the streamwise direction، the streamwise wavelengths of these structures increase with a small ratio. With the Weber number increase، the streamwise wavelength is significantly decreased while the spanwise wavelength has no remarkable change. A Reynolds number that defined with streamwise distance، jet velocity and viscosity is proposed to estimate the onset of interface structure، and Reynolds number is equal to 42000 in this paper.
Keywords: Liquid jet; Interface structure; Wavelength; Transition position
  
 Numerical Investigation of Forced Convection of Nanofluid Flow in Microchannels: Effect of Adding Micromixer A. Ababaei , A. A. Abbasian Arani , A. Aghaei * Pages 17591772 Abstract Full Text [PDF 1631KB]   In the present study، forced convection of CuO–water nanofluid in a two dimensional parallel plate microchannel with and without micromixers has been investigated numerically. Two horizontal hot baffles were inserted between the adiabatic plates and three vertical baffles، which were attached on the plates، worked as micromixers in order to improve the cooling process. The effect of Reynolds number، Re = 10، 30، 60، 100، and 150 and nanoparticles volume fraction، from 0 to 4%، were examined on flow field and heat transfer. Different geometrical configurations for the arrangement of the hot baffles were tested. A FORTRAN code based on finite volume method was developed to solve the governing equations and SIMPLER algorithm was used for handling the pressurevelocity coupling. Simulations showed that the presence of micromixers and increasing the Reynolds number as well as nanoparticles volume fraction، increase the average Nusselt number. In order to achieve maximum heat transfer، best arrangements for the baffles were reported. It was also observed that the size of recirculation zones، which are created behind the micromixer baffles، increases with increasing Reynolds number and leads to better cooling.
Keywords: Forced convection; Microchannel; Micromixer arrangement; KooKleinstreuer nanofluid model
  
 A Balloon Model Examination with Impulsion of CuNanoparticles as Drug Agent through Stenosed Tapered Elastic Artery S. Ijaz * , S. Nadeem Pages 17731783 Abstract Full Text [PDF 1361KB]   In this speculative examination، main focused is to address Cunanoparticles application in an inclined stenosed elastic artery with balloon model examination. Flow of blood in an inclined stenotic artery is investigated mathematically by considering its behavior as viscous fluid. The dimensionless terms of temperature، velocity، resistance to blood flow and stress on wall of stenotic inclined artery has been computed by using mild stenosis approximation. The model is also used to understand the significance of overlapping stenosed artery with tapered angle and inclination angle. At the end، the results confirmed that the impulsion of copper as drug agent minimized the amplitude of the resistance to blood flow and hence nanoparticles plays an important role in engineering as well in biomedical applications.
Keywords: Blood flow; Overlapping stenosis; Balloon model; CuNanoparticles
  
 Peristaltic Pumping of a Generalized Newtonian Fluid in an Elastic Tube A. N. S. Srinivas* , C. K. Selvi , S. Sreenadh Pages 17851798 Abstract Full Text [PDF 465KB]   The paper investigates the peristaltic pumping of an incompressible nonNewtonian fluid in an elastic tube with long wavelengths and low Reynolds number approximations. Carreau fluid model is considered for present study to describe the peristaltic flow characteristics of non Newtonian fluid in an elastic tube. Carreau fluid is a generalized Newtonian fluid which exhibits Newtonian behaviour for 1 n and it resembles as a powerlaw model at higher shear rates. For 1 n it exhibits shearthinning property، i.e.، the apparent viscosity reduces with increasing shear rate. The equations governing the fluid flow are solved with usual perturbation expansion by taking Weissenberg number i W as a perturbation parameter. The expressions for axial velocity، stream function and volume flow rate as function of pressure difference are derived. The effects of various pertinent parameters on variation of flux for a Carreau fluid flow through an elastic tube along with peristalsis are calculated and interpreted through graphs. The pressure rise per wavelength and shear stress distribution for different values of physical parameters are calculated and presented. Trapping phenomenon is presented graphically to understand the physical behaviour of various parameters. The difference in flux variation is examined by two different models of Rubinow and Keller (1972) and Mazumdar (1992). It is observed that in elastic tubes، the flux of Carreau fluid with peristalsis is more when the tension relation is a fifth degree polynomial as compared to exponential curve. When the powerlaw index 1 n or Weissenberg number 0 iW and without peristalsis، the present results are similar to the observations of Rubinow and Keller (1972). Further، the relation between the function () g a and radius of the elastic tube for both Newtonian، nonNewtonian cases are discussed graphically and these findings are identical with the investigations of Mazumdar (1992). The results observed for the present flow characteristics reports several interesting behaviours that warrant further study of physiological fluids in elastic tubes with peristalsis.
Keywords: Peristaltic flow; Elastic tube; Nonnewtonian fluid; Weissenberg number; Powerlaw index
  
 Effects of Aspect Ratio in Moulded Packaging Considering Fluid/Structure Interaction: A CFD Modelling Approach M. H. H. Ishak , M. Z. Abdullah* , M. S. Abdul Aziz , A. Abas , W. K. Loh , R. C. Ooi , C. K. Ooi Pages 17991811 Abstract Full Text [PDF 1139KB]   The fluid/structure interaction (FSI) investigations of stacked chip in encapsulation process of moulded underfill packaging using the twoway Coupling method with ANSYS Fluent and ANSYS Structural solvers are presented. The FSI study is executed with different aspect ratio of stacked chip on the mould filling during the encapsulation process. The simulation results in the FSI study is well validated with experimental setup. The epoxy moulding compound (EMC) and structure (chip) interaction is analyzed for better understanding the FSI phenomenon.Von Mises stresses experienced by the chip also be monitored for risk of chip cracking. The proposed analysis is anticipated to be a recommendation in the chip design and improvement of 3D integration packages.
Keywords: Air void; Deformation; Moulded packaging; Stacked chip; Aspect ratio
  
 Numerical Analysis of Mixed Convective Peristaltic Flow in a Vertical Channel in Presence of Heat Generation without using Lubrication Theory B. Ahmed * , T. Javed , A. H. Hamid , M. Sajid Pages 18131827 Abstract Full Text [PDF 456KB]   In this paper، heat transfer analysis of peristaltic mixed convection flow through a vertical channel is presented in addition، effects of heat generation are also investigated. The mathematical model is represented by the system of nonlinear partial differential equations. The analysis is made in the presence of nonzero wave and Reynolds numbers. The results of the long wavelength assumption in a creeping flow can be deduced. These results thus predict new features in the peristaltic transport in the absence of the approximation of long wave length and low Reynolds number. The moderate finite elements based technique has been used to compute the highly accurate solution of the governing problem. To ensure the accuracy of the computed solution، the results obtained are validated against the available results in the literature and found good agreement. The obtained result are presented through graphs and the influence of involved pertinent parameters is analyzed.
Keywords: Mixed convection; Peristaltic flow; Heat generation; Numerical analysis; Nonzero Reynolds number
  
 Linear and Weakly Nonlinear Models of Wind Generated Surface Waves in Finite Depth A. Latifi * , M. A. Manna , P. Montalvo , M. Ruivo Pages 18291843 Abstract Full Text [PDF 586KB]   This work regards the extension of the Miles’ and Jeffreys’ theories of growth of windwaves in water of finite depth. It is divided in two major sections. The first one corresponds to the surface water waves in a linear regimes and the second one to the surface water waver considered in a weak nonlinear، dispersive and antidissipative regime. In the linear regime، we extend the Miles’ theory of wind wave amplification to finite depth. The dispersion relation provides a wave growth rate depending to depth. A dimensionless water depth parameter depending to depth and a characteristic wind speed، induces a family of curves representing the wave growth as a function of the wave phase velocity and the wind speed. We obtain a good agreement between our theoretical results and the data from the Australian Shallow Water Experiment as well as the data from the Lake George experiment. In a weakly nonlinear regime the evolution of wind waves in finite depth is reduced to an antidissipative Kortewegde VriesBurgers equation and its solitary wave solution is exhibited. Antidissipation phenomenon accelerates the solitary wave and increases its amplitude which leads to its blowup and breaking. Blowup is a nonlinear، dispersive and antidissipative phenomenon which occurs in finite time. A consequence of antidissipation is that any solitary waves’ adjacent planes of constants phases acquire different velocities and accelerations and ends to breaking which occurs in finite space and in a finite time prior to the blowup. It worth remarking that the theoretical amplitude growth breaking time are both testable in the usual experimental facilities. At the end، in the context of wind forced waves in finite depth، the nonlinear Schrödinger equation is derived and for weak wind inputs، the Akhmediev، Peregrine and KuznetsovMa breather solutions are obtained.
Keywords: Surface waves; Wind waves; Interface waves; Rogue waves; Blowup; Asymptotic models; Miles’s mechanism; Jeffreys’ mechanism
  
تاريخ انتشار: 12/9/96 تلفن: 33915271 (031)
تاريخ درج در سايت: 12/9/96
شمار بازديدکنندگان اين شماره: 69




