فهرست مطالب

Journal Of Applied Fluid Mechanics
Volume:18 Issue: 3, Mar 2024

  • تاریخ انتشار: 1403/10/12
  • تعداد عناوین: 20
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  • D. Wang, C. Song, C. Qiu, W. Wang, Y. Xu, P. I. Mihailovich * Pages 535-548
    As a necessary component of a turboshaft engine, optimizing components in the radial pre-swirl system is critical for improving turbine performance. The aim of this study was to investigate the impact of receiver holes on the flow and heat transfer characteristics of various components in the pre-swirl system. Large-eddy simulations were used to demonstrate the phenomenon that the different receiver hole tangential angles have a significant influence on the performance of the radial pre-swirl system. In addition, a mathematical model was developed to predict the relative total pressure and temperature inside the co-rotating cavity. It is observed that the relative total pressure of computational model with receiver hole tangential angle equals to 15° is 21.88% and 18.54% larger than that of the computational model with receiver hole tangential angles equals to 0° and 7.5°as a result of the increase in swirl ratio. A larger swirl ratio resulted in a stronger centrifugal supercharging effect and jet acceleration effect. Furthermore, the Nusselt number and the field synergy angle exhibited an upward and downward trend, respectively. Subsequently, an investigation of unsteady characteristics designed to reveal the vortex state inside the co-rotating cavity was carried out. The mathematical model’s prediction result matched the LES result closely, demonstrating its practical significance.
    Keywords: Aeroengine, Radial Pre-Swirl System, Pressure Drop, Temperature Drop, Nusselt Number, Coherent Structure
  • X. Zhu, X. Han, C. Xie, H. Zhang *, E. Jiang Pages 549-566
    The present work aims to investigate the influence of vane clocking effect on fluctuating characters and radial force on impeller for centrifugal pump. Numerical simulations were conducted with validation by experiments, at four different relative angular position between vane and tongue. The power consumption and work done by blades are evaluated in time-history. The radial velocity, circumferential velocity at impeller-diffuser clearance is depicted by expanding the turning surface, for comparison under different diffuser position to reveal the flow distortion affected by clocking effect. The results indicate that when vane trailing edge is at tongue (θd1), the corresponding diffuser channel is placed against small flow section in volute leading to a blocking effect that results in significant circumferential inhomogeneity at diffuser outlet. The interaction between impeller blade and different diffuser vane presents distinct intensity, causing the unsteady fluctuation intensity of power consumption of impeller at different vane positions is significantly different, and so is the radial force. As the diffuser vane moves away from tongue (at θd4), the blocking effect reduces and the flow field becomes more evenly distributed among each channel. Resulting in weaker fluctuations in the power consumption, blade load and radial force.
    Keywords: Clocking Effect, Centrifugal Pump, Vaned Diffuser, Blade Load, Blocking Effect
  • S. Venkatesh *, R. Krishnaraj, P. M. Gopal, V. Kavimani Pages 567-584
    The performance of the settling chamber was examined in two scenarios in this study. In case 1, the settling chamber collection efficiency and flow characteristics were predicted without a baffle plate. In case 2, the settling chamber performance was predicted with the baffle plates. In case 2, two baffle plates were placed between the inlet and exit nozzle. The experimental set up was fabricated with the baffle plates to measure the performance. Moreover, the efficiency of the settling chamber was determined for the different inlet velocities. The Variable Frequency Drive (VFD) controller was adopted with the suction fan to vary the inlet velocity. The Reynolds Stress Model (RSM) was used to forecast the settling chamber flow characteristics. In cases 1 and 2, the best capture efficiency results were achieved at 2.5 m/s inlet velocity. The experimental study shows that the settling chamber gathering efficiency was 45% at 52.35µm. It is 44.4% higher than case 1. In CFD analysis, the settling chamber efficiency was 43%. The variation between the experimental and CFD results was 4.4%. The observations show that the pressure drop for the baffle plate setting chamber was increased 4.37 % compared to case1. The maximum settling velocity of the case 1 and case 2 chambers is 1.62 m/s and 2.81 m/s respectively. It indicates that the baffle plate chamber has highest setting velocity. Moreover, the hopper region has highest tangential velocity when introducing the baffle plate. The observations show that the radial velocity is increased in the rectangular wall region compared to hopper region due to the baffle plate.
    Keywords: Baffle Plate Effects, Flow Pattern Of Particles, Pressure Drop, Kinetic Energy Of The Particles, Terminal Settling Velocity, Particle Settling Time
  • A. Ferfouri, D. D. Jerković *, N. Hristov, A. V. Kari, T. Allouche Pages 585-600
    The present paper evaluates the performance of grid topologies and RANS turbulence models in predicting the aerodynamic drag coefficient of a 155mm artillery projectile by conducting steady-state computational research. The research is performed for Mach numbers from 0.5 to 3.0, assuming axisymmetric flow. Four distinct combinations of grid topology and turbulence model are investigated, where the O- and C-grid topologies are each paired with both the realizable k-ε and the SST k-ω models. Compared to the experimental data across the Mach number range, the combination of O-grid with k-ε model showed the smallest mean deviation of 1.64%, while the combination of O-grid with k-ω exhibited the largest mean deviation of 5.54%. In terms of drag component results, both turbulence models and grid topologies performed equally in predicting pressure and friction drag, with differences less than 6% in all Mach number cases. However, significant discrepancies were obtained in base drag prediction, especially between the two turbulence models, with differences reaching around 60% in the transonic regime. This was identified as the main contributor to the discrepancies in aerodynamic drag coefficient results among the four combinations. Furthermore, the findings indicate that the turbulence model selection impacts the zero-yaw drag prediction more than the grid topology, especially in the transonic and low supersonic cases.
    Keywords: Aerodynamic Drag, Artillery Projectile, Drag Components, Grid Topology Type, RANS Turbulence Model
  • A. Nasseroleslami, A. Sarreshtehdari *, M. S. Seif Pages 601-616
    Evaluation of cavitation erosion risk, whether through numerical (CFD) or experimental methods, is crucial in many fluid flow design processes. This risk correlates directly with cavitation signals on affected surfaces. The aim of this study is to optimize the placement of piezoelectric sensors to investigate cavitation-induced erosion on solid surfaces and to enhance the numerical evaluation of their correlation with recorded signals from the sensors. In this study, based on the technical specifications of the K23 tunnel, a convergent-divergent channel has been designed to reduce the pressure in its test section below the vapor pressure, thereby creating the potential for bubble formation on the sample plate. Within this channel, four semi-cylindrical bluff bodies have been utilized as the most effective obstacles to increase cavitation erosion. A quick method for identifying cavitation erosion involves applying a special color to the sample plate. The Film Applicator has been employed as the optimal tool for achieving a uniform color and a thin paint layer on the sample plate. Through CFD modeling, potential cavitation zones are identified under various test conditions to refine the placement of piezoelectric sensors in experimental tests. As a result, piezoelectric sensors are positioned more accurately to measure sound pressure levels. The sound pressure levels obtained using piezoelectric sensors in the time domain, are compared with erosion-induced cavitation zones on the sample test surfaces. The strong agreement between sound pressure levels and observed erosion on the sample plates confirms the accuracy and improvement in the placement of piezoelectric sensors based on CFD modeling.
    Keywords: Placement Of The Piezoelectric, Erosion, Sound Pressure Level, Cavitation Tunnel K23, Bluff Body
  • W. Han, Y. Xing *, R. Li, W. Li, Y. Hao, Y. Chen Pages 617-630
    Understanding the kinetic behavior at the scale of a single bubble is crucial for understanding cavitation flow properties. In this study, experiments and numerical analysis of shock waves resulting from the crumpling of a solitary adjacent wall vacuole have been conducted. Shock wave characteristics induced by near-wall bubble collapse were investigated using high-speed photography and shadowgraphy techniques. Numerical simulations were conducted of near-wall vacuole collapse-induced shock-wave dynamics using the OpenFOAM cavitatingFoam solver. (1) The shock wave displays an essentially symmetrical distribution. The pressure maxima diminished along the sagittal diameter. The intensity of the second shock wave generated near the wall was decreased by approximately 21.2% compared to the initial shock wave. The simulated wave speeds exhibit a high level of concordance with the experimental data, and the calculated errors are below 7.9%. (2) The pressure and velocity at which the shock wave propagates in water exhibit a power function and an exponential decay function, respectively, as they travel across distance. And the perturbation profile of the velocity aligned with the direction in which the shock wave propagated. This result indicates that the shock wave acts as a catalyst for the creation of disturbances in the velocity field. (3) Constructing a transformation relation for the wave energy of near-wall vacuole collapse. During its first collapse, the near-wall cavitation bubble lost an average of 85% of its energy. This allowed for the assessment of the erosive impact of cavitation-induced shock waves on rigid surfaces.
    Keywords: Cavitation Bubble, Cavitation, Pressure, Shockwave, Wave Energy, High-Speed Photography High-Speed Photography
  • K. Anusindhiya, G. Vinayagamurthy *, K. Sathish Kumar Pages 631-640
    Study on the behavior of jet flows are important for various reasons especially in the fields of aerospace, mechanical engineering, and environmental science. In aerospace engineering, understanding how jets behave can assist in increase / decrease thrust, decrease drag, improve fuel efficiency and reduce jet associated noise in aircraft engines and rockets. The flow control of jets is necessary for faster mixing and spreading, which can lead to much important aspects of noise reduction. Passive flow control of jets for various advantages like noise reduction, better mixing and thrust vector control is achieved by using mechanical slotted tabs. The effects of the slotted rectangular tabs are studied experimentally at different nozzle pressure ratios of 3, 4 and 5. The study involves the usage of three different novel configurations of rectangular slotted tabs for jet flow control. The Tabs A, B and C are designed with a blockage of 7.3% which are placed diametrically opposite to each other at the exit of a converging nozzle of 13 mm exit diameter. The centerline total pressure profiles, radial total pressure profiles and shadowgraph images for the tabbed cases are retrieved from the investigation and the results are compared with the free jet to study and visualize the jet mixing characteristics of the tabs. The results proved that tabs are found to be effective in enhancing the mixing and thereby reducing the acoustical characteristics of the jets. Tab C is seen to perform better in enhancing the mixing compared to other tabs with a percentage reduction of 89 %, 86 % and 84 % for the Nozzle Pressure Ratio (NPR) 3, 4 and 5 respectively.
    Keywords: Flow Control, Rectangular, Slotted Tabs, Centerline, Shadowgraph
  • F. Marzban, M. Marzban, K. Mohammadzadeh *, A. Abadeh Pages 641-660
    This paper investigates the thermal behavior of non-Newtonian nanofluids, specifically carboxymethyl cellulose (CMC) 0.5% and Al₂O₃ nanoparticles, in the fully developed region of a horizontal annulus. A three-dimensional axisymmetric, steady-state numerical solution is performed using the mixture multiphase model to compare with the results obtained from the single-phase model. The present study examines the effects of nanoparticle volume fraction ranging from 0.5% to 1.5% and particle diameters of 25 nm and 50 nm for various Reynolds numbers (Re) within the laminar flow regime. The results indicate that while the temperature profile distribution is slightly affected by changes in alumina concentration, significant variations are observed in the entrance region. Specifically, as Re is enhanced, the Nusselt number (Nu) is increased. For an outer wall heat flux of 1000 W/m² and a 1% concentration, Nu at the x/L = 0.25 section augments from 6.92 to approximately 13.14 as Re is enhanced from 5 to 500. Additionally, for the same conditions, Nu is about 0.78% higher for Al₂O₃ nanoparticles with a diameter of 25 nm than the ones with a diameter of 50 nm. In all cases, there is an acceptable agreement between the results obtained from the mixture and the single-phase models, with discrepancies of less than 1.13%.
    Keywords: CFD Simulation, Carboxymethyl Cellulose, Non-Newtonian Nanofluids, Entrance Region, Convective Heat Transfer
  • H. Yang, D. Luo *, T. Wang Pages 661-677
    The intricate and complex flow structures of three-dimensional unsteady incompressible turbulence surrounding bluff bodies have garnered considerable attention from numerous researchers. Using computational fluid dynamics (CFD) methodologies, the underlying mechanism by which a wavy trailing edge (TE) design for a D-shaped bluff body achieves drag reduction was explored. The wavy TE was in the form of a cosine wave with two design parameters: amplitude and wavelength. To ascertain optimal control parameters, we employed an improved delayed detached eddy simulation (IDDES) technique for a comprehensive parametric analysis, focusing on the amplitudes and wavelengths of the cosine wave. Furthermore, to gain a more holistic understanding of the factors influencing the design of wavy TE structures, we conducted parametric studies on three distinct groups of wavy structures. After identifying the optimal amplitude, wavelength, and wave type, we further investigated the control mechanism of the wavy structures in reducing the drag and mitigating lift fluctuations for Reynolds numbers in the range 3.6×105–3.6×106. Present investigation revealed that compared with the original D-shaped bluff body, the wavy TE structures significantly reduced the average drag coefficient, with a maximum drag reduction of 60.2%. Moreover, it effectively curtailed the fluctuations in the lift coefficient. With careful parameter adjustments, the wavy TE significantly enhanced the characteristics of the flow field. This improvement was evident in the reduction in vortex scales, enhancement of instability characteristics in separated shear layers, and effective suppression of periodic vortex shedding.
    Keywords: D-Shaped, Passive Control, Wavy Trailing Edge, Drag Reduction, Control Mechanism
  • T. Harish Ragavendra *, P. A. Anupama, K. S. Jai Pranesh, D. Lakshmanan, R. Abinaya Pages 678-697
    Over the decades, polar satellite launch vehicles and geosynchronous launch vehicles have utilized variants of the Vikas engine for numerous space operations. The pitching control for those launch vehicles is achieved by gimbaling the Vikas engine nozzle up to ± 4° with mechanical actuating parts. This research investigation dealt with the design modification, analysis, and estimation of performance parameters in the modified Vikas nozzle configurations intended for fluidic thrust vectoring control. Hence, the technique of interest in this investigation was to assess the effects of the fluidic throat skewing technique in an adapted nozzle configuration of the Vikas nozzle. The distinct design configurations were initially iterated with the design of experiments (DOE) method to estimate and adopt an optimum nozzle configuration with higher thrust vectoring effectiveness. The computational analysis utilized the k-e Reynolds-averaged Navier-Stokes (RANS) numerical model. The flow characteristics of the resolved nozzle configuration were analyzed and validated under three distinct sonic mach freestreams. Finally, air was employed as the secondary fluid in the injector plenum, and the analysis was carried out by varying the secondary mass injection rates. The analysis results depicted that the implemented fluidic injection thrust vectoring approach was significantly effective by achieving ± 5° of tilt with a system thrust force ratio of 0.9190 for 9% of secondary mass flow rate injection.
    Keywords: Computational Analysis, RANS Based Model, Distinct Sonic Mach, Throat Skewing Control, System Thrust Force Ratio
  • N. Shah, A. Prajapati, H. B. Mehta, J. Banerjee * Pages 698-709
    Microchannel heat sinks (MCHS) are capable of removing exceptionally high heat fluxes through liquid-to-vapor phase transition, making them suitable for various applications, including the thermal management of high-power microelectronics. However, their commercial applicability is hindered by the flow boiling instability associated with chocking of the micro-passage as the vapor bubbles grow. The present study addresses the research gap in literature pertaining to the impact of microchannel depth on flow boiling instability in terms of amplitude of heated surface temperature and pressure drop oscillations, and their influence on heat transfer performance. Experiments are conducted using dielectric water boiling in multiple parallel microchannels with mass fluxes of 220 and 320 kg/m²s and wall heat fluxes ranging from 25 kW/m² to 338 kW/m². Two different MCHS, fabricated from oxygen-free copper substrate, were examined, each comprising 44 parallel microchannels with nominal depths of 500 µm and 1000 µm, and a consistent nominal width of 200 µm. Heat transfer coefficients were measured using an array of embedded T-type thermocouples on the substrate to measure temperature gradients. The findings reveal that increasing the microchannel depth results to a significant increase in the amplitude of wall temperature fluctuations under fixed wall heat flux conditions, which in turn diminishes heat transfer performance. Additionally, the study demonstrates a notable dependence of pressure drop on coolant flow and both microchannel sizes. This research provides new insights into optimizing MCHS design for enhanced thermal management, highlighting the critical role of microchannel depth in mitigating flow boiling instability and improving overall heat transfer efficiency.
    Keywords: Boiling Heat Transfer, Microchannel, Instability, Boiling Curve, Channel Depth
  • K. Liu, Z. Wang, Q. Liu * Pages 710-727
    Surface roughness of ski suits can have a significant effect on the aerodynamic performance of ski jumping athletes. Herein, several typical surface roughness configurations are examined through numerical simulations. Force parameters such as lift, drag and pitching moment are analyzed to evaluate the aerodynamic performance of varying surface roughness. Furthermore, the athlete model is segmented into distinct body parts to conduct a comprehensive analysis of the aerodynamic contributions from each individual segment. Generally, the surface roughness has a significant effect on the aerodynamic performance during the flight phase. Specifically, the lift-drag ratio of the entire multibody system shows a trend of increasing first and then decreasing. Moreover, the trunk of the athlete plays a predominant role in generating aerodynamic forces during the flight phase. Therefore, when designing high-performance ski jumping suits, prioritizing the surface roughness of this part can be considered first. Flow structures are also presented to analyze the impact of these various surface roughness conditions. Notably, flow suppression near the back region of the athlete body can significantly reduce the resistance force in the horizontal direction. Consequently, this revelation of the impact mechanism of ski suit surface roughness on the aerodynamic performance of the multibody system can guide the design of appropriate ski suits, and will also assist athletes in achieving superior aerodynamic performance during flight.
    Keywords: Ski-Suits, Surface Roughness, Aerodynamic Performance, Numerical Simulation
  • K. Singh *, A. Singh, D. K. Singh Pages 728-741
    In a centrifugal pump, the clearance flow is quite common due to the existence of clearance between the casing and impeller. Apart from the clearance, the impeller speed and flow rate have a significant impact on fluid frictional torque. This study uses experimental and numerical methods to investigate these dynamics. The experimental setup includes measurements of fluid frictional torque at various levels of axial clearance (0.6 mm, 1.2 mm, and 1.8 mm), flow rates (8 L/min, 10 L/min, and 12 L/min), and impeller speeds (800 rpm, 1000 rpm, and 1200 rpm). A 3-level, 3-factor factorial design (L27) is employed to systematically examine the impact of these factors on fluid frictional torque. Response Surface Methodology (RSM) and Artificial Neural Networks (ANNs) are utilized to capture complex parameter interactions, with optimization performed using a Desirability Function (DF). The analysis reveals a significant increase in fluid frictional torque with increasing axial clearance, impeller speed, and flow rate. The optimal operational parameters for minimizing fluid frictional torque in the centrifugal pump are identified as    and mm, achieving a minimum fluid frictional torque of 0.499 Nm
    Keywords: Fluid Frictional Torque, ANOVA, RSM, ANN, Optimization
  • A. Vinoth Raj *, C. Senthil Kumar Pages 742-755
    This study investigates the influence of propeller slipstream on the aerodynamic characteristics of a Transition Micro Air Vehicle (TMAV). The TMAV under consideration comprises a cylindrical body, planar wing, and X-tails. Wind tunnel testing and numerical simulations were performed on TMAV configurations both with and without a propeller at various advance ratios (J = 0.45, 0.55, 0.65, and 0.75). The angle of attack ranged from -8° to +8° in increments of 4°, and from +8° to +16° in increments of 1°. The findings indicate that propeller slipstream significantly alters the flow field around the TMAV components, leading to a reduction in overall aerodynamic performance and stability. Specifically, the slipstream downwash decreased the lift and drag of the port wing and certain tails, while the slipstream upwash increased the lift and drag of the starboard wing and other tails, resulting in earlier stall occurrences under slipstream conditions. Furthermore, it was observed that aerodynamic performance improves as the propeller advance ratio decreases. The data obtained from this study elucidate the effects of propeller slipstream on the aerodynamic performance of wing and X-tail combined MAVs. Currently, there is a lack of literature addressing the effects of propeller slipstream on the aerodynamics of wing and X-tail combined MAV configurations. This study provides valuable insights into the aerodynamic behavior of this TMAV under the influence of propeller slipstream.
    Keywords: Interactional Aerodynamics, Wings Downwash, X-Tail Deflection Effects, Multiple Reference Frame (MRF) Technique, MAV Stability
  • Y. Qiao, W. Chu *, H. Zhang, K. Wang, X. Yang Pages 756-768
    Surge phenomenon is investigated for an axial compressor through a set of experiments. In addition, the full-annulus numerical simulation method is used to numerically simulate the surge phenomenon and analyze the flow field details during the surge process. The results identified four distinct stages in the surge: forward deceleration, reverse flow, forward recovery, and chamber recovery. The forward recovery stage, the flow field experiences stall with the occurrence of unevenly distributed stall regions. In contrast, the chamber recovery stage at the same flow rate exhibits a more uniform flow field without stall regions. These findings highlight the capability of the capability of the full-annulus calculation method to provide insights into the flow field details during the surge process. The information can serve as a reference for the development of accurate surge models and the study of the influence of surge on the internal flow of the compressor passage.
    Keywords: Axial Compressor, Surge Process, Flow Field Details, Full-Annulus Calculation, Numerical Simulation
  • P. P. Gohil *, V. Patel, A. U. Mehta Pages 769-786
    A high velocity is rarely accessible in water streams such as rivers, canals, and outlets of sewage and common effluent treatment plants. However, an average velocity of 0.5 - 1.0 m/s is reported to be available in many water streams most of the time. Hydrokinetic (HK) turbines can extract power from the flowing water in these streams. Considering the small quantum of power generated, the economic factor is more significant than efficiency. A Savonius-type HK turbine can generate energy from low-velocity magnitudes of around 0.5 m/s, although it remains a low-speed and low-efficiency turbine. In this study, an attempt has been made to computationally investigate the performance of the Savonius turbine in a water stream channel. It is observed that the performance of the Savonius turbine is not significant, and the generated power cannot be utilized constructively for different applications. Therefore, it is necessary to develop and investigate variant constructive systems to enhance turbine performance. This manuscript focuses on exploring these variant systems and understanding their performance characteristics. Four variant systems have been selected: (i) System-1: Solely Savonius turbine, (ii) System-2: Savonius turbine with a flume, (iii) System-3: Deflector section used before the flume, and (iv) System-4: Deflector section used before the turbine. The investigation was carried out for these four variant systems using the Fluent commercial code. The results indicate that the Coefficient of performance (Cp) is low for System-1, solely Savonius turbine, with a value of 0.052. For the other variants, Cp values were found to be 0.357, 1.385, and 0.579 for the turbine with a flume, deflector before the flume, and deflector before the turbine respectively at the Tip Speed Ratio (TSR) is 1. Moreover, the study also extends to optimizing Cp under different TSR for the different variant systems. The intention is to use this study to install an HK turbine with an optimum constructive structure for maximizing and stabilizing the power that can be used for an isolated application.
    Keywords: Computational Method, Low Water Velocity Magnitude, Hydrokinetic Turbine, Variant Constructive Systems, Fluent Commercial Code
  • V. Patel *, V. Buch Pages 787-797
    This study explores the impact of compression ratio (CR) and fuel blends on the combustion properties of a diesel engine fueled by conventional diesel and biodiesel derived from Moringa oleifera. The research was conducted on a single-cylinder diesel engine with variable compression ratio (VCR) and common rail direct injection (CRDI), utilizing diesel and Moringa oleifera biodiesel blends MB10, MB20, and MB30. The experimental conditions included varying the CR between 15:1 and 18:1, maintaining an injection timing of 23°before top dead center, injection pressure set at 600 bar, and an engine speed of 1500 rpm under 100% load. The findings revealed that increasing the CR raises cylinder pressure (CP), cumulative heat release rate (CHRR), and rate of pressure rise (ROPR) for all the tested fuel blends. Notably, the diesel exhibited the highest CP of 70.83 bar, CHRR of 1.36 kJ, and ROPR of 6.42 bar/°CA (degree per crack angle) at a CR of 18:1. Among the biodiesel blends, MB30 showed the highest CP of 69.21 bar, while MB10 displayed highest CHRR and ROPR of 1.5 kJ and 6.17 bar/°CA, respectively. Furthermore, the net heat release rate (NHRR) and mean gas temperature (MGT) decreased with rising CR for all tested fuels. At a lower CR of 15:1, the diesel showcased the highest NHRR and MGT of 69.75 J/°CA and 1303.69 °C, respectively, whereas, in the case of biodiesel blends, MB20 demonstrated the highest values of 67.53 J/°CA and 1287.39 °C, respectively, at the same CR. Meanwhile, the ignition delay (ID) and combustion period diminish with a rise in the CR for all tested fuel blends. At a higher CR of 18:1, the minimum ID and combustion duration for diesel were reported as 17°CA and 15°CA, respectively. For the biodiesel blends, MB10 and MB30 showed a minimum ID of 16°CA, while MB10 and MB20 exhibited minimum combustion duration of 15°CA at the same CR.
    Keywords: Moringa Oleifera Biodiesel, VCR-CRDI Type Diesel Engine, Combustion Characteristics, Ignition Delay, Combustion Duration
  • J. Zhu, B. Liu, J. Sheng, S. Zheng, T. Lu, X. Chen * Pages 798-808
    The dynamic behavior of a glycerol aqueous droplet impacting on a thin water film was experimentally investigated with a high-speed camera. Numerous splash behaviors with different impact velocities (2.0-4.5 m/s), liquid film thicknesses (140-700 μm) and glycerol solution concentrations (30 wt%, 60 wt% and 80 wt%) were statistically analyzed, and finally classified based on morphological features. The laser-induced fluorescence images illustrate that the prompt splash secondary droplets mainly originated from the thin water film, while the components of delayed splash secondary droplets came from both the glycerol aqueous droplet and the thin water film. The results show that increasing viscosity suppresses prompt splash,  inhibits the crown expansion and accelerates the crown collapse, while decreasing droplet viscosity facilitates prompt splash. The decreasing film thickness promotes passive delayed splash and increases the crown height. A splash morphology regime map was presented based on Weber number, dimensionless film thickness and solution mass concentration, delineating a threshold between prompt splash and coalescence. It also found that the occurrence of crown lamella rupture is sensitive to the film thickness and We.
    Keywords: Droplet Impact, Thin Liquid Film, Crown, Splash, Secondary Droplet
  • M. A. Ali, P. Mondal * Pages 809-820
    Shock Wave Boundary Layer Interactions represent a complex flow feature combining high-speed inertial force - dominated flows with low-speed viscous force dominated regions. In this research, planar oblique shock impingement on finned missile body (slender body) have been studied, involving a complex flow field of shocks and expansion waves. Computational studies are used to perform quantitative and qualitative analysis of multi body configurations and investigate the associated flow physics. There is change in induced forces and moments of finned body with change in location of shock impingement, due to the combined effect of enhanced compression, expansion and flow pitch angle on different regions of the missile. For fixed lateral separation between the bodies, changes in coefficient of forces and moments of missile body are very small for shock impingement locations close to fin leading edge. The fins contribute about 50-60% to coefficient of forces and moments of finned missile body. With change in angle of incidence, there is change in polarity of forces and moments illustrating extreme sensitivity of missile body to location of shock impingement, which is due to the combined effect of enhanced compression and expansion on different regions of the missile.
    Keywords: Shock Wave, Boundary Layer, Finned Missile Body, Shock Impingement, CFD
  • L. Zhang, R. Xie, H. Jia * Pages 821-834
    The water-entry process of solid and hollow hyperelastic spheres was numerically simulated using the arbitrary Lagrange–Euler method, based on the finite element analysis software LS-DYNA. The effect of the different initial velocities on the cavity evolution and deformation of the sphere in a range of low Froude (Fr) numbers was investigated. The evolution of the cavity, deformation of the hyperelastic sphere and parameters at the time of cavity closure were analysed. In addition, the difference in the water-entry process between solid and hollow spheres was given. The numerical results shows that the size of the cavity, fluctuation on the cavity profile, closure time and closure depth increased with Fr and that the closure time was proportional to Fr1/2 for both solid and hollow spheres. However, the relationship between the closure depth and Fr of the hollow sphere differed from that of the solid one. Within the investigated low Froude numbers, whether for the solid or hollow spheres, the deformation amplitude increased with the Froude number. However, the deformation period remained nearly the same for different conditions. Under the same physical and motion parameters, the hollow sphere exhibited larger deformations compared with the solid sphere. The deformation period for the hollow sphere was also longer than that for the solid one.
    Keywords: Water Entry, Fluid-Structure Interaction, Deformation, Cavity, Closure Time