Journal Of Applied Fluid Mechanics
Volume:16 Issue: 7, Jul 2023

Scour-induced sediment erosion poses a significant threat to the safety and longevity of infrastructure, including bridges, wind turbines, elevated buildings, and coastal infrastructure. Despite the well-known destructive consequences of scour, accurate models that capture the complexity of its dynamics remain elusive, impeding the development of effective countermeasures. We provide a comprehensive review of existing literature on scour dynamics and examine the fluid dynamics and bed shear stress surrounding bridge piers. We propose CFD (Computational Fluid Dynamics) simulations with LES (Large-Eddy Simulation). The current paper demonstrate that LES is a more effective technique than RANS (Reynolds averaged Navier-Stokes) for investigating bridge scouring. The LES simulations study local scour induced effects and compare the findings with RANS simulation results. Besides, two countermeasures are modeled, delta vane and plate footings, to decrease scour around piers. The results show that both countermeasures effectively reduce the shear stress, and we also suggest a combination of a delta vane and a plate footing as a promising solution to reduce upstream and downstream bed shear stress. The paper highlights the importance of thorough investigations on bridge scouring and the need for effective countermeasures to protect infrastructure from scour-related damage or collapse. The recommended countermeasures hold significant promise to reduce construction and maintenance costs and extend infrastructure longevity.

It is essential to maintain the aerodynamic performance of the air-conditioning system meanwhile reducing the noises (including aerodynamic, broadband, and discrete noises), determining the consumer's comfort level. In this work, depending on the coupling of the wavy leading-edge and the seagull airfoil, the aeroacoustics noise and aerodynamic performance of the impellers with the coupling bionic blade were investigated in detail. The results indicate the aerodynamic performance was improved by the coupling bionic optimization. Moreover, the total pressure efficiency (η) of the coupling bionic blade increases by 2.28% in comparison to the original blade. Furthermore, A smaller static differential pressure is observed between the suction and pressure sides, and vortices and backflows from the pressure side to the suction side are hampered, causing a reduction in turbulence noise. Additionally, the broadband noise of the coupling bionic blade decreases by 3.59 dB. Besides, the coupling bionic blade improves the directivity of the sound pressure level, especially in the middle-frequency and low-frequency region, resulting in a decrease of 7.9 dB for the aeroacoustics noise of the coupling bionic blade. What's more, the modal analysis demonstrates the security of the designed coupling bionic blade. In generally, this work provides some inspiration to design axial flow fans with excellent aerodynamic performance and low-noise characteristics.

The hard landing of the spent stage of promising launch vehicles (LV) in the designated areas of the fall leads to the collapse of the structure, the spillage of the remnants of the guaranteed fuel reserve, the outbreak of fires, and, as a result, require large expenditures for the complete elimination of man-made consequences. Residues of the guaranteed fuel are additional stocks of propellant components in the rocket blocks of the stage of LV, designed to compensate for the disturbing factors acting in flight on the LV. They are characterized by carcinogenic and mutagenic effects on the environment. The article considers the issue of extraction of unprocessed residues of guaranteed fuel. An experimental stand and a program for conducting experiments have been developed to study the extraction process. The purpose of the study is to conduct a comparative analysis of the results of mathematical modeling and physical modeling. Based on the results of the physical experiment, a mathematical model, and the results of a comparative study of two types of models are presented: The calculated heat carrier (HC) temperatures at the experimental model setup (EMS) inlet (according to the first law of thermodynamics and the Navier-Stokes equations) and the measured HC temperature at the EMS inlet during experiments were compared.

In order to reduce the temperature in the marine engine cabin, improve the working environment of the staff and meet the economy and emission requirements, the cooling system of the engine was experimentally investigated in the present study. In this regard, water cooling and air-cooling schemes were studied and the main indicators including engine torque, smoke-emission, and exhaust temperature were analyzed. The obtained results indicate that the highest torque can be obtained from the air-cooling turbine case and air-cooling exhaust pipe. As the applied torque decreases, the outlet smoke first decreases then increases and decreases finally. Moreover, it is found that the water-cooling turbine case and water-cooling exhaust pipe increase the smoke. When the turbocharger is equipped with a water-cooling turbine case and water-cooling exhaust pipe, the higher the engine torque, the higher the turbine exhaust temperature and oil tank temperature, and the greater the reduction of the exhaust temperature. The engine torque is in direct proportion to the fuel consumption. The greater the torque, the higher the engine speed and the greater the fuel consumption. The engine torque is inversely proportional to the fuel consumption rate. The greater the torque, the smaller the fuel consumption rate. In cases with water cooling exhaust devices at 110% loading speed, the temperature after the intercooler is higher than that with the air-cooling exhaust device. After the intercooler, the pressure increases as the applied torque increases, and a higher-pressure ratio can be obtained from the air-cooling exhaust device. The higher the engine torque, the higher the temperature of the turbine exhaust, the higher the outlet temperature of the circulating cooling water, and the higher the temperature in the cabin. It was concluded that the exhaust device of the air-cooling turbine case and water-cooling exhaust pipe can reduce the temperature in the engine parts by up to 2℃, thereby improving the working environment of the cabin staff, economic performance, and the emission index.

During recent years, microfluidics based microelectromechanical systems (MEMSs) have found multiple applications in biomedical engineering. One of their most important implementations is fluid transfer in microliter and nanoliter scales. Nowadays, micropumps are extensively used in various medical applications such as drug delivery. In this study, the performance of a piezoelectric micropump is investigated and optimized. This micropump consists of a pump chamber and three deformable walls in a nozzle-diffuser shape, which are used to create pressure gradient between the inlet and outlet. The performance of the micropump is evaluated by transient Computational Fluid Dynamics (CFD) simulation using dynamic mesh. Then its performance is optimized using the Design of Experiment (DOE) method based on mean net outlet mass flow rate and flow reversibility at the pump outlet. The results indicate an improvement of 34.5% in mean net outlet mass flow rate and a significant decrease in reversibility. The maximum mean net outlet mass flow rate and the minimum reversibility corresponding to the optimum geometries are 95.82 mL/min and 0.05%, respectively.

Finding the right texture pattern to effectively improve the sealing performance of the floating ring gas film seal has always been a topic of interest for engineers. Herein, to reveal the effect of the rectangular textured base shape on the sealing characteristic parameters of floating ring gas film seal, four bottom shapes of rectangle, isosceles triangle, left triangle and right triangle were proposed. The governing equations were solved by the finite difference method and the correctness of the theoretical results was verified by the test bench. The effect of operating conditions parameters on the sealing performance were also analyzed. The results reveal that the trends of the experimental results is consistent well with the theoretical results, in which the relative errors are all less than 9%. It indicates that the theoretical model is scientific and valid. As the speed and inlet pressure increase, the texture bottom shape significantly changes the distribution of pressure and temperature field. And the average gas film thickness determines whether the texture produces an effect or not. Under the same operating conditions, a right-angled triangular bottom shape can obtain a good stability and cooling effect for the sealing device. With a bottom shape of the right triangle and a bottom shape of the rectangle, the maximum difference in opening force and gas film temperature rise were calculated to be 234.91 N and 0.61 oC, respectively. The research results provide theoretical support for further study of the textured floating ring gas film seal and a reference for texture optimization.

In order to cool the gas turbine vane or blade and raise the operating temperature, two standard convective cooling methods are used: jet impingement cooling and film cooling. The current study uses computational analysis to analyze and compare film cooling effectiveness with and without multi-jet impingement cooling on a flat plate. Ansys Fluent software is used to perform computational analysis on a flat plate. The computational results were compared with the experimental result using K-ω SST turbulence model and validated with literature data. The flat plate is used for the conjugate heat transfer study on the hot surface (named interaction surface), cold surface (called target surface), and inside the film hole. Different heat transfer parameters such as heat flux, Nusselt's number, and effectiveness are compared for the two cases, i.e., film cooling with impinging jets (IFC) and film cooling without impingement cooling (FC). It is observed that the FC case shows lower effectiveness as compared to the IFC case. The average Nusselt number for the IFC cases is almost three times larger than FC. The film exit temperature values are higher FC case, but it is more uniform in the IFC case. Interaction surface heat flux and Nusselt number values show higher values on the upstream wall of the film hole for IFC than in the FC case.

The flight of the owl is silent owing to non-smooth leading edges of the owl’s wings and the curved serration of the feathers. This study applied this concept of bionics to blade design for horizontal axis wind turbines to reduce aerodynamic noise. The flow and sound field distribution around a rotating wind turbine with three blades were investigated. A numerical simulation method that combines large eddy simulation (LES) and FW-H acoustic equation was adopted to compare aerodynamic noise between the blade prototype and the bionic blade. The comparison revealed that the sound pressure level of the bionic blade was reduced over middle and high frequencies, thereby achieving a noise reduction of 6.9 dB. The intensity of the wake vortex shedding of the bionic blade was lower, and the interaction between the shedding vortices in the bionic blade was smaller compared with that in the prototype blade, indicating that the aerodynamic noise induced by the shedding vortex was effectively reduced.

This study focused on reducing the drag force of a road vehicle using passive flow control. The aerodynamic performance of the model vehicle was improved by applying originally designed vortex generators. The drawing data of the model vehicle and vortex generators were designed in the Solid Works® program. The drag force measurements and flow visualizations were performed in the Fluent® program with the Reynolds numbers in the range of 2.8×105-6.6×105. Accordingly, the CD value of the base model vehicle decreased by 6.22%, 4.59%, 3.38%, and 3.04%, respectively, using the originally designed vortex generator. This aerodynamic improvement rate can decrease the fuel consumption of vehicles by up to 3.3% at high vehicle speeds. To verify the highest numerical drag reduction, the model vehicle and vortex generators were produced in a 3-D printer. The vortex generators were mounted on the vehicle models with the lowest CD value as in CFD analysis. The wind tunnel tests were conducted under the same test conditions for two vehicle models. It was determined that the experimental results supported numerical drag reduction.

Semi-open centrifugal pump has the disadvantage of low efficiency in chemical industry for its unique structure. For the purpose of improving its efficiency as much as possible on the premise of meeting the head demand, in this case, an optimization strategy combining Bezier curve, Genetic Algorithm (GA), Fuzzy Logic (FL), Artificial Neural Network (ANN) and solution space model based on stratified sampling is proposed to optimize the efficiency of semi-open centrifugal pump. The fourth-order Bezier curve is used as parametric method to control the blade profile, GA combined with FL is used as optimization strategy to seek the optimal individual. Besides, the optimization solution space based on stratified sampling method and ANN training are used to shorten computing time. Finally, the semi-open centrifugal pump corresponding to the optimal parameter combination of blade profile has been found, and on the premise of meeting the head requirements, the efficiency has been significantly improved. Entropy production rate is carried out to analyze the reason of efficiency improvement. The whole optimization strategy proposed in this study provides a good reference for parametric control and performance optimization of bladed pump.

Shock waves are one of the primary damage parameters of an ammunition explosion. Therefore, accurately obtaining the shock wave pressure distribution law after ammunition explosion is greatly significant for the ammunition damage power evaluation and the guidance of ammunition selection in the operations course. This study established the mapping function between the surface reflected and free-field shock wave pressures, considering the altitude effect on shock wave pressure. Finite element numerical simulation analysis of typical (trinitrotoluene) TNT explosive quality and static explosion shock wave pressure test were performed, and the model calculation accuracy was verified by using the obtained shock wave pressure data. The Validation results show that the model had 84% calculation accuracy and could well reflect the explosion shock wave pressure distribution law. Furthermore, the results provided a new calculation method and scientific data support for the accurate evaluation of the damage power of an ammunition explosion. Additionally, the results are significant for applications in engineering testing and the military.

The hydrodynamics characteristics in a tank with an up-down reciprocating disc agitator were numerically investigated using computational fluid dynamics (CFD) simulations. A dynamic mesh technique along with a user-defined function (UDF) was used to solve the reciprocating movement of the disc agitator in the tank. The dynamic flow field and averaged values of some important parameters were obtained. The verification of the simulation was completed by comparing its results with experimental data in the literature. It is found that the flow pattern in the tank with a reciprocating agitator is characterized by two dynamic vortices, which are above and below the disc, respectively. Flow field, force acting on the disc and power requirement change periodically in the tank. The increase of frequency, amplitude and disc diameter leads to the increase of the averaged velocity in the tank as a whole. Nevertheless, the uniformity of velocity distribution is slightly improved, worsened and greatly improved respectively under the above operating conditions. The averaged values of the force acting on the disc and power consumption are in the second and the third power relations with the reciprocating frequency and amplitude, respectively. The ratio of fluid averaged velocity in one cycle to averaged disc speed, and Newton number are hardly affected by reciprocating frequency and amplitude, while they increase with the enlarged size of the disc agitator.

An experimental investigation has been undertaken to determine the effects of plain and notched base flaps on the drag performance of simplified tractor-trailer combination without any intermediate gap, Generalized European Transport System (GETS). Both plain and notched base flaps are rigid, made up of three identical flaps whose length is equal to the width of the GETS model, and not angled inward or outward. The experiments examined three-sided flap configurations corresponding to various combinations of seven heights of the plain part (from 10 to 40 mm in steps of 5 mm), four notch amplitudes (from 2.5 to 10 mm in steps of 2.5 mm), and five notch wavelengths (from 10 to 50 mm in steps of 10 mm). It is shown that the drag performance of the plain flap at zero yaw highly depends on the height of the plain flap. The maximum drag reduction occurs for e/w=0.1 yielding a drag reduction of 1.9% when compared to the GETS model without flap (baseline GETS). It was shown that the time-averaged drag coefficient increased slightly until a maximum was reached at e/w=0.3 but then decreased slightly with increasing e/w. Under zero yaw angle conditions, GETS model with a notched base flap, e10-a05.0-λ20, gives the lowest drag. The addition of this base flap to the GETS model resulted in a 2.8% drag reduction. This notched base flap was shown to be more effective not only at reducing under yawed flow conditions tested but also at reducing time-averaged side coefficient under yawed flow conditions tested, compared to the e10-a00.0-λ00 flap.

Multi-wing centrifugal fans are wildly used in the central air-conditioning. The influence of dimensionless clearance of the volute-tongue on aerodynamic performance and noise is studied by numerical simulation and experimental tests in this paper. The complicated internal flow related to unsteady flow in a centrifugal fan with multiple wings is investigated by numerical simulation. Besides, the influence of circumstance on the noise is analyzed. It is testified that the internal flow of centrifugal fans is ameliorated using appropriate volute tongue clearance. Reduced eddy current decreased the local-flow loss near the volute tongue and exit. The experimental results show that the static pressure of model △t/R2=0.12 rose to 7.5 Pa and the aerodynamics noise value reduced to 4 dB compared with that of a reference model. Meanwhile, an obvious reduction of aerodynamics noise by 3.74 dB is obtained for model △t/R2=0.12 installed in the air conditioning unit. The static pressure of centrifugal fan is significantly improved for the model with a cochlear tongue clearance ratio of △t/R2=0.12. It is further demonstrated that the proper dimensionless distance effectively suppresses the aerodynamic noise of forward multi-wing fans.

Drift Flux model is widely used in literature to predict void fraction in two-phase gas-liquid flow. Drift flux model has been used for all flow regimes. The distribution parameter implemented in the model is very crucial for the accuracy of the model. A new distribution parameter was developed in this paper as a function of two dimensionless parameters and flow regime (slug or plug). The new model showed a superior predicted void fraction accuracy over all available models in literature. In this paper, the influence of the flow regimes was implemented in the formulation of the drift flux model distribution parameter for the first time in literature. The drift velocity was found to be negligible in the horizontal configuration. The proposed model was validated using unbiased data from literature from different sources and for a wide range of liquid viscosity from water up to high viscosity oil (600 cP) and pipe diameter from 19 mm up to 152 mm. The mean relative absolute error of the proposed model using all data bank is around 16% while the least error model available in literature is around 19%. Moreover, the most recent models of Rassame and Hibiki (2018) and Kong et al. (2018b) give 33% and 50%, respectively.