مهدی نیلی احمدآبادی

This paper investigates the effect of a Helmholtz resonator with one or two pairs of deep cavities on the mixing chamber of a subsonic ejector to determine its impact on the ejector's entrainment ratio. The study utilizes numerical analysis, where the depth, location, and number of cavities were varied while keeping the width of the resonator constant. The Fluent software solved the Unsteady Reynolds-Averaged Navier-Stokes equations with the k- εturbulence model. The presence of the cavity at the beginning, middle, and end of the mixing chamber reduced the entrainment ratio by 0.6%, 3.8%, and 6.6%, respectively, and the presence of the second cavity at the positions of 20, 40, and 60 mm with respect to the first cavity reduced the entrainment ratio by 9.9%, 10.1%, and 10.2% respectively. The depth effect was studied at a distance of 20 mm for a pair of cavities at depths of 75, 100, and 125 mm causing a reduction of 4.9%, 9.9%, and 13.1% in entrainment ratio. The study also observed longitudinal and pulsating oscillations inside the mixing chamber due to the simultaneous filling and emptying of opposite cavities. Furthermore, the amplitudes of the pressure oscillations in the first pair were weaker than those in the second pair. In the final part of the research, the effect of primary flow fluctuation was also investigated, the results of which showed that the primary flow fluctuation increases the entrainment ratio by 5.2% due to the increase of effective mixing between the primary and secondary flow.

Laser cladding technology has received much attention in recent years. Injection of powder by carrier gas through the nozzles plays an important role in the quality and control of the laser cladding process, so it is important to be studied. In this study, a two-phase flow of gas-powder metal from the nozzle in a laser-cladding process is numerically simulated and compared with the results of an experimental study of the nozzle output to confirm the numerical simulation. The three-dimensional simulation was carried out steadily by Ansys CFX software. Experimental study is carried out by the visualization of powder flow. The results of the experimental study and the numerical simulation are in good agreement. In the next section, the effects of various parameters such as particle flow rate, carrier gas flow rate and shielding gas flow rate on particle concentration are investigated. The simulation results showed that by decreasing the carrier gas flow rate, the maximum concentration of particles increases and the particles concentration location gets closer to the nozzle outlet. Also, increasing the powder flow rate only increases the concentration of the particles and has no effect on the other parameters of the powder flow. The change in the shield gas flow rate also has no effect on the powder flow behavior.

In conventional passenger cars, two-third of the energy is wasted from the exhaust gas and engine cooling system. The present study has investigated the performance of a waste heat recovery (WHR) system based on the Organic Rankine Cycle (ORC) for the turbocharged gasoline direct injection engine. The optimal working conditions along with the best working fluid of the organic Rankin cycle to obtain the maximum net output power (NOP) from the recovery cycle are investigated. The steady-state zero-dimensional thermodynamic model of basic ORC at a series of engine operating conditions is designed in Thermoflex software. The working point of the engine has obtained by simulation of vehicle performance based on the standard urban driving cycle. Considering numerous and varied working fluids, 23 working fluids including pure and mixture fluids are evaluated. The mass flow rate of working fluid, condenser pinch, turbine inlet pressure, and condenser working pressure are considered as the optimization design variables and the optimum operating conditions of the basic ORC extracted for each working fluid using the Downhill Simplex method. Finally, by having experimental data for 320 points of the engines map, the efficiency of the optimized basic cycle was analyzed in combination with engine’s entire operating region. The results showed that R-507a, R-410a and R-125 present highest NOP respectively which indicate better performance of zeotropic and Azeotropic mixtures in engine WHR by ORC and for the best case, NOP reached to 2.6 kw in small load region and 6.6 kw in the peak thermal efficiency region.

The aim of inverse design problems is achieving a geometry corresponding to the wall target pressure distribution. One of the newest inverse design methods, was Elastic Surface Algorithm (ESA) in which the airfoil wall was modeled as a flexible curved beam and the difference between target and current pressure distributions in each iteration was the deformation factor of the airfoil wall. The first version of ESA used for the inverse design of sharp leading edge blade of axial flow compressors, is subject to oscillation, instability and divergence due to high pressure gradients on the blade leading edge. Therefore, it cannot be used for a sharp leading edge blade. The purpose of this research is to develop ESA for axial-flow compressor cascade with sharp leading edge blades. The main basis of this Improvement is paying attention to the deflection curve of the beam, which is continuous and differentiable in all points. The physical property of Timoshenko’s beam in large deformations is used in the upgraded version without applying any geometric filtration to eliminate the fractures of the intermediate profiles. In order to increase the displacement of the beam at each iteration, an optimal relationship between the beam characteristics including the elasticity modulus, the thickness and width of the beam is used. Finally, the upgraded version has been validated in a few cases for subsonic inviscid flow regime. The results indicate the robustness, flexibility and high convergence rate of the upgraded ESA in the design of axial-flow compressor blades.

Breakwater or submerged obstacle is one of the methods used for protection of the coast. Breakwaters cause dissipation of wave energy by generation of turbulence flow and vortices. In this study, by insert a rectangular obstacle against a solitary wave, the generation and evolution of vortices have been investigated by using Particle Image Velocimetry (PIV) technique. The PIV results show due to flow separation, two vortices are formed around the front and back edges of the obstacle when the solitary wave approaches the obstacle. The closer the wave approaches the obstacle, the larger the vortices are. When the formed vortex over the front edge of the obstacle approaches its end, these two vortices are merged together and form a larger vortex. In the following, the reduction of wave height before and after the obstacle is measured through a wave gage altimeter sensor. The results show the existence of obstacle decreases up to 3% of wave height in comparison to that without obstacle. Finally, by integrating pressure and momentum flux from the PIV results around the obstacle, the drag force applied to the obstacle is obtained.

In the present work¡ an inverse design algorithm called Ball-Spine (BSA) is developed as a quasi-3D method on the meridional plane of a centrifugal pump impeller with rotating frame and incompressible viscous flow within it¡ with the aim of improving its performance. In this method¡ numerical analysis of viscous flow on a thin plane of flow between two blades using a 3D viscous flow solver is combined with BSA¡ which modifies hub and shroud geometries. Namely¡ instead of solving inviscid quasi-3D flow equations in the meridional plane¡ full 3D Navier-Stokes equations is solved on the thin plane of flow. To show the validity of the present work¡ centrifugal pump is numerically evaluated and numerical results are compared with experimental results¡ and flow field in the meridional plane of pump impeller is obtained using quasi-3D method. By studying the algorithm in the rotating geometry and choosing static pressure and reduced pressure as target parameters the ability of performance of the algorithm is assessed. After that¡ the new impeller geometry is obtained in conformity with the modified pressure distribution¡ by defining target pressure distribution on the hub and shroud surfaces of the conduit and trying to eliminate excess pressure gradients. Obtained results indicate good rate of convergence and desirable stability of BSA in the design of rotating conduits with incompressible viscous fluids. By using the above-mentioned optimization method following results was observed: increase of static pressure along streamline¡ 1% of increase in the pump total head¡ delay in impeller cavitation inception.

In this study, the centrifugal fan of a cooling turbine is numerically investigated and is then compared with the experimental results at a performance point. The experimental performance characteristics of the fan are as: rotational speed and flow parameters at the inlet and outlet of the fan. In this cooling turbine, the fan is used for cooling of the turbine inlet air flow. The aims of this study are obtaining the fan performance characteristics curve and 3D numerical simulation inside the fan. Rotor and case modeling is respectively conducted using Blade Gen and Catia software, the grid generation of the rotor domain and fan casing is respectively accomplished by Turbo Grid and Ansys Mesh software and finally, 3D numerical solution of flow inside the fan is done by CFX software. In the CFX software, compressible flow equations are solved using pressure based method with SST turbulence modeling. To verify the numerical results, grid independency is investigated. Finally, the numerical results are compared with the experimental results that shows a good agreement.

In this paper, one-dimensional design of centrifugal compressor with inverse design of 90-degree bend duct between radial and axial diffuser is accomplished using an iterative method. In the design procedure, all overall dimensions of the centrifugal compressor including impeller, vanned radial diffuser, 90-degree bend duct and axial diffuser are computed. To evaluate the results, after the geometry modeling and grid generation, 3-D flow field in the whole compressor are numerically analyzed using CFX software. The numerical simulation shows that there is a high loss region through the 90-degree bend between the radial and axial diffuser because of its high curvature. In order to reach a minimum loss in the 90-degree bend duct, the aerodynamic design of the 90-degree bend duct is carried out using an inverse design method. At the first step, the shape modification capability of the 90-degree bend duct is evaluated by linking up the Ball-Spine inverse design algorithm and CFX software. Then, the geometry is modified by improving the hub and shroud pressure distribution and applying it to the inverse design code. Finally, the designed compressor with the modified 90-degree bend duct is analyzed. The results show that, the total pressure ratio and overall efficiency increases about 3 and 4 percent, respectively.

The purpose of this paper is to investigate theLow-Density Lipoproteins (LDL) mass transfer in vessel walls using the Lattice Boltzmann Method (LBM). High Schmidt number of LDL leads to numerical instability of LBM.In order to solve this problem, LBM and finite volume method (FVM) are combined.In this hybrid method, the blood velocity field is solved by LBM using the single relaxation time, SRT, model and FVM has been used for LDL concentration equation. LBM is able to simulate flow and mass transfer for the Schmidt number, Sc, up to 3000 only if the time consuming multi relaxation time is used. However, the purposed hybrid method suggested in this article can be used to solve the problem for Sc as high as 107. Good agreement between our results obtained from the hybrid simulation and the available results in the literature and noticeable decrease in CPU time compared with when the LBM is used for both flow and mass transfer, indicates the ability of the hybrid method.Finally, the hybrid methodis used to simulate the mass transfer of LDL particles and investigate the effective factors for increasing the surface concentration, such as the size of LDL particles, wall suction velocity, wall shear stress, Newtonian and non-Newtonian fluids behavior and change of concentration boundary layer with various Schmidt number.

Three-dimensional numerical analysis of rotating components of a turbo-shaft engine including 3 stages axial compressors and one stage centrifugal compressors is performed by CFX software. Compressible flow equations are solved by using pressure based method and SST turbulence model. After grid study, compressor performance curve are obtained by changing the boundary conditions of the compressor inlet and outlet. The results show that there is a secondary flow from hub to tip in the first stage of axial compressor because of its high axial chord length. Also, flow in the first stage rotor is transonic. Moreover, in the centrifugal compressor, secondary flow phenomenon, jet-wake region and slip phenomenon at the impeller outlet are obtained from the numerical analysis.

In this research an inverse design algorithm, called ball-spine algorithm (BSA) is developed on a 90-degree bend duct between the radial and axial diffuser of a centrifugal compressor with viscous swirling inflow to bend duct. The shape modification process integrates inverse design algorithm and a quasi-3D analysis code. For this purpose, Ansys CFX software, is used as flow solver and inverse design algorithm is written as a code inside it. Shape modification is accomplished for viscous and inviscid flow to check the effect of viscosity on convergence rate. Also, the effect of swirl velocity in shape modification process is investigated, by considering increased pressure as the target parameter. The algorithm reliability for swirling flow is verified by choosing different initial geometries. Finally, aerodynamic design of the bend duct with BSA is accomplished to reduce losses in 90-degree bend. Shape modification process is carried out by improving the current wall pressure distribution and applying it to the inverse design algorithm. Results show that convergence rate and stability of BSA are favorable for designing ducts with swirling viscous flow. So that, the pressure recovery coefficient of the 90-degree bend duct is 4%increased.

The purpose of this study is the aerodynamic design of 20 kW horizontal axis wind turbine using blade element momentum with 3D numerical analysis of flow around it. First, the aerodynamic coefficients curves of an airfoil are considered as input. Then, the geometrical characteristics of different blades including chord length, twist angle, relative angle and diameter of blades are calculated using this method. To select the best airfoil as wind turbine blade, power coefficient of 10 different airfoils are calculated and then compared to each other using the blade element momentum method. Also, to improve the performance, three airfoil types called NACA63-215 on the hub section, Riso A1-24 on the midsection and FX63-137 on the tip are used instead of just on eairfoil type from hub to tip. Designed blade is simulated and analyzed in ANSYSCFX software. In order to consider the effects of blades rotation, two domain solutions are used for flow analysis. The surrounded area around the blades is divided into the inner rotating and outer stationary regions. In both design and analysis steps, the results are validated with the other authoritative works in this field.

Wind tunnels generate controlled air flow which passes through the model. Thus، a series of useful data related to air flow quality are obtained. The final goal of wind tunnel design is to generate a uniform air flow with minimum turbulence intensity and low flow angle. One of the methods for decreasing the turbulence intensity is to install honeycomb and screens in the settling chamber of the wind tunnel. In this research، the effects of honeycomb and screens with specified geometric parameters on velocity distribution، turbulence intensity، skewness and flatness are investigated. A set of hot-wire anemometer is used to measure turbulence intensities. It measures flow instantaneous velocity with high frequency. The results show that the installation of honeycomb and screens، and isolation of the test section from the fan decreases the turbulence intensity of the test section about 75% and، optimizes the skewness and flatness values. Moreover، normal probability distribution of instantaneous velocity approaches the normal distribution.

The ratio of lift to drag coefficient in wind turbine blades is within the most important parameters affecting the power coefficient of wind turbines. Due to the performance of Magnus wind turbines in low speed air flow; such turbines are attractive for research centers. In the present work, a new geometry for the blades of Magnus wind turbines is defined. The defined geometry is based on the geometry of a Treadmill with a difference that the diameter of its leading circle is greater than that of its trailing one. In the present work, the body is supposed to a low speed air flow while a tangential velocity is applied to the airfoil surfaces and then, its effect on the lift and drag coefficient is studied by numerical method. The effect of generated tangential velocity on the surfaces is investigated for different air flow speed and attack angles and then, its results are compared with that for stationary surfaces. The results show that generating tangential velocity along the surfaces caucuses the lift and drag coefficients and, their ratio to be varied, greatly. By the tangential movement of the surfaces, the maximum ratio of lift to drag coefficient occurs in zero attack angle which is equal to 109. Moreover, maximum magnitude of lift to drag coefficient for attack angles 5, 10, and 15 degrees are 81, 64, and 57; respectively.

The growing use of industrial machinery, household appliances and etc, has increased undesirable noises. Thus, the need to control and reduce the undesirable noises in a closed space has caused a lot of interest in recent years. In this paper, the behavior of sound waves in a closed space is investigated using finite difference time domain method. For this reason, firstly, the wave equation is derived using the mass and momentum conservation equation and adiabatic state equation for an ideal compressible fluid. Then, the boundary condition equation for a closed space is obtained using the momentum conservation law and wall impedance equation. The obtained equations are discritized based on the finite difference time domain method. Finally, the wave equation is solved under the wall boundary condition with arbitrary absorption coefficient and impulse source initial condition. The results show the capability of the method for solving this kind of problems.

Inverse design is one of the design methods of aerodynamic ducts such as S-duct intakes. In these problems، the geometry of the duct is unknown but the pressure distributions along the walls are given. In this paper، a new inverse design method called “flexible string method” is introduced. In this method، the duct walls are modified from initial guess to final shape based on the flexible string movement algorithm according to pressure distribution. In 3D design، the duct design process starts with a 2D one. At first step، a 2D Jet-Engine S-shaped air intake considering flight mach number is designed using the inverse design method based on an Euler flow solver (with no considering the jet nose engine effects). At the second step with considering duct sections like circle، ellipse and bean the 2D duct is modified to obtain the 3D duct. Finally، it is validated by analyzing the duct flow in 3D turbulent regime. The numerical studies show in spite of severe height change with respect to duct length، there is no separation in the duct and the uniformity of flow at the duct exit is completely satisfactory.

In the current study، the phenomenon of free convection around a metal cylindrical with uniform heat flux is experimentally investigated using PIV technique. The experimental tests are performed in a qubic container that contains liquid water with free surface which a metal rod horizontally passes through it. To create a two-dimensional flow، two parallel planes are inserted in the container and then، the metal rod is passed though it. The tests are performed for different heights of water and their results are compared with each other. To measure flow velocity in a specified region، the PIV technique is used. The tests are implemented by using a 200 mW laser and a CCD camera of 25 fps. In the experiments، the particles having the same density of water are tracked through the container in a specified time interval to calculate the flow field around the rod. sequence analyses of flow field during the different moments obtains the unsteady flow field. Although removing the 3D effects of flow، the results show that the flow field is strongly oscillatory and unsteady.

In this study، the radial flow turbine of a cooling turbine is investigated numerically and then compared with the experimental results at some operation conditions. Performance characteristics of the compressor are obtained experimentally by measurements of rotor speed and flow parameters. In this investigation، the turbine performance curve is obtained and three dimensional flow field in the turbine is analyzed. The rotor and casting geometry are modeled in BLADE GEN and CATIA softwares respectively. The TURBO GRID software is used for grid generation of rotor while the ANSYS MESH software is applied for grid generation of casting. Finally، 3D numerical solution of fluid flow in the turbine is solved by CFX flow solver. In this approach، compressible flow equations are solved according to the pressure based method with SST turbulence model. To ensure the numerical results، the grid independency is studied. Finally، the performance characteristics of the turbine are obtained numerically which are then compared to the experimental results. The comparison shows good agreement between numerical and experimental results.

In this research, an aerodynamic design of axisymmetric diffuser is performed via linking a solver of boundary layer equations, Genetic Algorithm and Ball Spine inverse design algorithm (BSA). A numerical boundary layer code is incorporated to the genetic algorithm to reach an optimum pressure distribution on the diffuser wall in such a way that maximum pressure recovery is obtained without separation. To validate the developed boundary layer code, the calculated quantities are compared with Blasius and Howart’s analytical results. Then, the optimized pressure distribution is considered as the "target pressure distribution" for the inverse design algorithm to find out the relevant optimum geometry. For inverse design, Ball-Spine algorithm as the geometry modification algorithm is compined by the Fluent software as the flow solver. Implementation of this combination is completed through User Defined Function (UDF) feature of Fluent. Having examined the performance of the proposed inverse design method, quantitative effect of this method on the performance improvement of an axisymmetric diffuser is studied. The numerical results of the optimized diffuser shows that its pressure recovery coefficient has been increased considerably.

In this research, the centrifugal compressor impeller of a turbo-shaft engine is studied. For this purpose, at first, its geometric specifications are exactly measured and then, the impeller geometric model is generated in the Blade-Gen module of Ansys software. This geometry is then reticulated in Turbo-Grid module and is numerically analyzed by applying the boundary conditions that can be obtained from the engine performance. The results are presented in the form of pressure ratio and efficiency curves versus the mass flow. After grid independency, some geometrical parameters (e.g. meridional profiles pages, the axial length and so on) that affect the performance of the compressor are investigated. Finally, the effects of geometric changes on the compressor performance curves are considered and the optimum compressor geometry equivalent to one with higher ratio of pressure and efficiency is introduced. In the modified compressor, the radial region of impeller to the whole ratio is 0.22 and the angle between the end of shroud wall and the vertical line is 6 degrees; moreover, the axial length of impeller increases by 5mm. By applying these modifications to the current compressor, the compressor efficiency and pressure ratio increases by 2.4 and 0.86 percent, respectively.

In this article, a special duct is introduced in which, inlet water jet initiates to oscillate after a short time and it causes the velocity and pressure to oscillate regularly. Considering that there is a linear relationship between the inlet jet velocity and its oscillations frequency, the flow rate can be calculated by measuring the pressure frequency. In order to study the flow field inside the current geometry of fluidic oscillator and also to find the optimum location for sensor to detect the pressure oscillation, the unsteady turbulent Navier-Stokes equations are solved by ANSYS CFX software. Having studied the grid independency, capability of K-ε and SST turbulence models for numerical simulation of unsteady flow inside the fluidic oscillator is considered. Then, according to the peak to average ratio (PAR) criterion, the qualities of pressure signals are compared at some points, to distinguish an optimum pressure sensor position. Afterwards, a prototype of fluidic oscillator flow meter is manufactured for the first time in Iran. Using this prototype and inserting the pressure and Piezoelectric sensor at the optimum point, the numerical simulation results are validated by the experimental data. Comparison between the numerical and experimental results shows that the SST model is more suitable for this flow simulation. Finally, by performing experiments in different flows, acquiring and processing pressure signals, the flow meter characteristic diagram (inlet jet oscillations frequency- inlet jet velocity) are extracted.

In this paper، at first a computer code was developed to design a one-dimensional vaneless volute related to radial inflow turbine. Absolute mach number and direction of the rotor inlet flow are the bases of the design method. In this method، the one-dimensional compressible flow equations are solved considering dissipation of the fluid flow. Free vortex flow equations were used to model (simulate) rotational fluid flow inside vaneless volute، using experimental (correlation) relations of angular momentum dissipation، energy dissipation، and deviation of rotational flow. In the next step، the volute is generated using the computes code. Then، the volute geometry was modeled three-dimensionally and after mesh generation، the inside flow is analyzed numerically in three-dimensional، compressible and viscous flow. At the end، the numerical results were compared to the initial design values. The comparison showed the validation of the design method. Keywords: Volute; Radial inflow turbine; Vaneless; one-dimensional design.

One of the most common facilities utilized in supersonic wind tunnels is multi-stage ejector system. In this system high speed air blowing with specified Mach numbers into the wind tunnel at predetermined points, helps to obtain the desired Mach number in the test section. In this study, according to characteristics of test section including Mach number, static temperature and stagnation pressure, relevant prominent features of the single-stage, two-stage and three-stage ejectors such as mass flow, velocity and stagnation pressure are computed. Two different aspects are implemented in solving governing equations of ejectors; first one is to assume the same Mach number for all ejectors and second one is based on assumption of the same stagnation pressure for the ejectors. It will be revealed that the later one is more optimal in comparison with the former criteria. Validation of the developed computational code results is performed via comparison with the experimental data of a wind tunnel operating at Mach number 2, which resulted in a difference of 5 to 7 percent. At the earlier section, design parameters of single ejector versus different mach numbers of the test section are presented and then effect of outlet static pressure reduction as a means of vacuum generation at the exhaust of the wind tunnel is discussed. Furthermore design of two-stage ejector according to both methods of equal Mach number and the same stagnation pressure is completed and in the last section three-stage ejector is studied base on the same stagnation pressure for comprising ejectors.

In this research, the aerodynamic design of a centrifugal compressor is carried out using an inverse design method. At the first step of the aerodynamic design, the shape modification capability of compressor meridional plane is generated by linking up the Ball-Spine inverse design algorithm as a shape modification algorithm and quasi 3D analysis code as a flow solver. Then, the meridional plane is modified by improving the hub and shroud pressure distribution and applying it to the inverse design code. At the second part of this research, by developing a novel design method on the blade to blade plane, and incorporating it into the quasi 3D flow solver, the 3D profiles of impellers will be obtained in order to reach the higher blade loading. Finally, to check the outcome of design process, the current and the modified impellers are analyzed using the full 3D flow solver, CFX. The results are the representatives of about 5 percent enhancement in compressor total pressure ratio.

In this study, a novel inverse design method is introduced for axisymmetric ducts in subsonic regimes. This method is an indirect one and starts with an initial guess. In this algorithm, the duct walls are simulated by hypothetical balls moving freely in specified directions, called spines. The advantages of this shape modification algorithm are high convergence rate and performing as a black box. Thus, the algorithm can easily be combined with any efficient flow solver. Based on this algorithm, the final nozzle propulsive force is increased about 7%.