Numerical Simulation Of Flow Field Research Articles

Numerical simulation of flow field and temperature separation in a vortex tube

A numerical analysis of flow field and temperature separation in a uni-flow vortex tube type is described. Effects of the turbulence modeling ( k– ε model and ASM), numerical scheme (hybrid, upwind and second-order upwind) and grid density on calculation of energy separation in the vortex tube are also conducted. It is found that the calculated results are in reasonably good agreement with the experimental data for both the static and total temperatures; the use of the ASM improves slightly the accuracy of the predictions than that the k– ε model. It is also observed that larger temperature gradients appear in the outer regions close to the tube wall for the static temperatures and the separation effect or the difference of the total temperature is high in the core region near the inlet nozzle. The maximum total temperature in the field is visible at the axis location of x/ D o between 0.5 and 1.0 for the ASM.

Method of internal 3D flow field numerical simulation for hydrodynamic torque converter

To enhance the performance of a hydrodynamic torque converter and thoroughly understand the trait of inside flow, a numerical simulation method of internal 3D flow for the three-element centrifugal hydrodynamic torque converter was systematically researched and expatiated in this paper. First, the internal flow field of each impeller was calculated. The curves that illustrate the relationships between the pressure differences of the inlet and outlet versus flux were drawn. Second, the concurrent working point of each impeller was approximately estimated. Finally, a calculation was performed considering the influence on each impeller. The flow field of a working point was solved by multiple calculations and the actual working condition was gradually determined. The pressure and velocity distributions of the flow field were proposed. The performance parameters of the hydrodynamic torque converter were predicted. The calculation method, and the proposed pressure and velocity distribution of the flow field, have practical significance for the design and improvement of a hydrodynamic torque converter.

激光熔覆中粉嘴流场的数值模拟

激光熔覆中粉嘴流场的数值模拟

THREE DIMENSIONAL MULTIPHASE COMPUTATIONAL FLUID DYNAMICS ANALYSIS OF VENTILATED SUPERCAVITATION

For some vehicles travelling through water,it is advantageous to cover the vehicle in a supercavity for the sake of reducing the drag acting on it. The method of artificial ventilation is most effective for generating and dominating the supercavity. This paper focuses on the numerical simulation of flow field around three dimensional body. The method is based on the multiphase computational fluid dynamics (CFD) model combined with the turbulence model and the full cavity model. The flow field of cavity is simulated by solving the compressible Navier-Stokes equations. The fundamental similarity parameters of ventilated supercavitaty flows that include cavitation number,Froude number,ventilation rate and drag coefficient are all investigated numerically in the case of steady flow and gravity field. We discuss the following simulations results in section 3: The variations of the cavitation number and the supercavity’s relative diameter with ventilation rate (subtopic 3.1); The drag coefficient versus the cavitation number (subtopic 3.2); Deformation of supercavity axis caused by gravitational effect for three different fixed Froude numbers—2.8,3.4,4.2 (subtopic 3.3). In subtopic 3.2,we give the comparison results of the drag reduction ratio among numerical simulation and experiment conducted in hydrodynamic tunnel and towing tank respectively. In subtopic 3.3,we summarize our discussion of gravitational effect on the axis deformation of supercavity as follows: In the case of smaller Froude number,the inclination of the cavity axis increases monotonously with increasing horizontal length,and reaches its maximal value at the end of supercavity; This deformation can be almost completely negligible when the Froude number Fr7. The comparisons with the experimental data in the hydrodynamic tunnel and the towing tank indicate that the present method is effective for predicting the flows around ventilated supercavity; that the numerical results is in good agreement with the experimental ones and that the maximal value of the drag reduction ratio can reach 88% compared with that the condition of fully-wetted.

Numerical Simulation of Flow Fields in A Natural Draft Wet-Cooling Tower

The flow field in the hyperbolic natural draft wet-cooling tower, which has great effects on the economy and security of power plant, was studied through numerical simulation. The mathematical model was established and analyzed in order to optimize the cooling-tower and to evaluate its efficiency. Various working conditions were considered and compared with each other, such as the circulating water flux, air temperature and tower resistance. It is concluded that when the cooling-tower runs without wind, there is a vacuum region inside the tower and the pressure rises with the increase of the tower height. Meanwhile, the inner flow field is axisymmetrical. The air velocity achieves its climax at the axis. It is also found that the effect of circulating water temperature is equivalent to that of the water flux.

Experimental measurement and numerical simulation for flow field and film cooling effectiveness in film-cooled turbine

Numerical simulation of three-dimensional flow field and film cooling effectiveness in film-cooled turbine rotor and stationary turbine cascade were carried out by using the κ-ɛ turbulence model, and the predictions of the three-dimensional velocities were compared with the measured results by Laser-Doppler Velocimetry (LDV). Results reveal the secondary flow near the blade surface in the wake region behind the jet hole. Compared with the stationary cascade, there are the centrifugal force and Coriolis force existing in the flow field of the turbine rotor, and these forces make the three-dimensional flow field change in the turbine rotor, especially for the radial velocity. The effect of rotation on the flow field and the film cooling effectiveness on the pressure side is more apparent than that on the suction side as is shown in the computational and measured results, and the low film cooling effectiveness appears on the pressure surface of the turbine rotor blade compared with that of the stationary cascade.

Numerical Simulation of Flow Field in High Reynolds Number Baffled Stirred Tank (Re=45000) and Experimental Verification

Unsteady flow in a baffled stirred tank of which Reynolds number based on the tip velocity and the radius of tank is 45000 has been simulated by solving numerically Navier-Stokes and continuity equations. LES model were used for sub-grid scale flows. Calculated results show unsteady flow fields in the whole region of the tank during about 16 complete impeller revolutions. As the results we present the occurrence and the disruption of large vortices, and the generation of many small eddies which are nearly homogeneous. The calculated visualized flow field, time-averaged velocity and turbulent intensity distributions are fairly in good agreement with the experimental data. It indicates that the present simulation procedure and results are applicable to describe the flow field in the real high Reynolds number baffled stirred tank. The calculated results also show the role of the baffle plate which blocks the tangential flow and induces the complicated flows that increase the stirring effect. The present results elucidate the unsteady flow mechanism in a high Reynolds number baffled stirred tank.

1012 IBM-FEMカップリング法による可変形粒子群を含む流れ場の直接数値シミュレーション(GS-5 粒子群の計測と解析)

1012 IBM-FEMカップリング法による可変形粒子群を含む流れ場の直接数値シミュレーション(GS-5 粒子群の計測と解析)

Three-dimensional flow field numerical simulation and analysis for conical spiral axial blood pump

ProE software is utilized to build the 3D model of the blood pump.Unsteady state 3D N-S equations,finite volume method based on non-structure grids and k-eturbulent model of computational fluid dynamic (CFD) technology are used to simulate the full three dimensional flow field of the blood pump numerically.The work of simulation and analysis focuses on the effects of the variation of the rotation speed and the angle of the rotating impeller on the flow field of blood pump.The simulation results show that the rotation speed and the angle of the rotating impeller of the blood pump should not exceed cer- tain value.Otherwise,the flow field will be too turbulent.If the rotating speed is too great,the characteristics of the pump will debase.The angle of the rotating impeller should be within certain value,otherwise the flow field can not keep steady.

CONJUGATE HEAT TRANSFER ASSOCIATED WITH A TURBULENT HOT AIR JET IMPINGING ON A CYLINDRICAL OBJECT

ABSTRACT Numerical simulation of flow field and thermal transport processes for a turbulent jet impinging on the surface of a cylindrical object, e.g., hot dog, were carried out at different jet velocities. Numerical predictions for average surface heat transfer coefficient were compared with the experimental results obtained using a lumped mass approach for model aluminum cylinders. Results indicated good agreement between the numerical and experimental results over the range of jet velocities, i.e., 10–40 m/s. Further experiments were carried out with real beef hotdogs to obtain center point temperature–time history during hot air impingement baking process. The experimental data agreed well with the numerical predictions when the impinging jet temperature was below 100C.

Numerical Simulations for Transport Aircraft High-Lift Configurations Using Adaptive Cartesian Grid Methods

Computations of complex flow fields around three-dimensional high-lift configurations using an adaptive Cartesian grid method and a cell-center finite-volume method are carried out and compared to wind-tunnel experiments. Because of complexities in both configuration and flowfield, there are great difficulties in numerical simulation of flowfields around transport aircraft high-lift configurations with leading slats and trailing flaps. In this paper, a modified Cartesian grid method is introduced to simulate the complex flow using the adaptive grid technique. The main emphasis is given to a multizone technique and a face-to-face algorithm and its applications. The multizone technique is employed to simplify the great difficulties in grid generation. The face-to-face algorithm is constructed to precisely establish the information exchange of flowfields on interfaces between zones. We solve Euler equations with a conventional algorithm, which includes a cell-center finite-volume method and an explicit four-stage Runge-Kutta time-stepping scheme in combination with a dual-time stepping approach. For three three-dimensional high-lift configurations, the numerical results are presented and analyzed. The computational results are in good agreement with the available experimental data show that the present method is feasible and effective for solving the flow around complex three-dimensional high-lift systems.

3932 正方形2重連結流れのシミュレーション(J08-1 流体情報学と発見科学(1),J08 流体情報学と発見科学)

3932 正方形2重連結流れのシミュレーション(J08-1 流体情報学と発見科学(1),J08 流体情報学と発見科学)

2422 直交格子法による光ディスクドライブ内部の流体解析(S41-3 流体機械に関連した複雑内部流動の解析と計測(計測・CFD),S41 流体機械に関連した複雑内部流動の解析と計測)

2422 直交格子法による光ディスクドライブ内部の流体解析(S41-3 流体機械に関連した複雑内部流動の解析と計測(計測・CFD),S41 流体機械に関連した複雑内部流動の解析と計測)

Numerical Simulation of Flow Field and Heat Transfer of Streamlined Cylinders in Cross Flow

The drag and convective heat transfer coefficients along the outer surface of lenticular and elliptical tubes with minor-to-major axis ratios of 0.3, 0.5, and 0.8 were determined numerically for cross-flow Reynolds numbers from 500 to 104. The two-dimensional, unsteady Navier-Stokes equations and energy equation were solved using the finite volume method. Laminar flow was assumed from the front stagnation point up to the point of separation. Turbulent flow in the wake was resolved using the shear stress transport k-ω model. Local heat transfer, pressure and friction coefficients as well as the total drag coefficient and average Nusselt number are presented. The results for streamlined tubes are compared to published data for circular and elliptical cylinders. Drag of the elliptical and lenticular cylinders is similar and lower than a circular cylinder. Drag can be reduced by making the streamlined cylinders more slender. Drag is relatively insensitive to Reynolds number over the range studied. An elliptical cylinder with an axis ratio equal to 0.5 reduces pressure drop by 30–40% compared to that of a circular cylinder. The Nusselt numbers of lenticular and elliptical cylinders are comparable. The average Nusselt number of an elliptical or lenticular cylinder with axis ratio of 0.5 and 0.3 is 15–35% lower than that of a circular cylinder.

THERMAL TRANSPORT IN A MULTIPLE JET IMPINGEMENT OVEN

ABSTRACT Three‐dimensional numerical simulation of flow field and heat transfer in a jet impingement oven with multiple jets was carried out. Distribution of local heat transfer coefficient on a model cookie in the oven cavity was obtained from the predicted flow and temperature fields, and compared with the experimentally measured values. Effects of air temperature (400, 450K) and air velocity (2.5, 5, 10 m/s), on the surface heat transfer coefficient were studied. Numerical predictions showed good agreement with the experimental results. It was found that heat transfer coefficient was a strong function of air velocity while air temperature had no effect on the heat transfer coefficient. Local heat transfer coefficient values ranged between 11 and 66 W/m2K whereas average heat transfer coefficient values ranged between 24 and 42 W/m2K. Results also showed that because of the presence of the suction fan in the oven, flow field near the model cookie surface was quite different from that for a jet impinging on a flat surface.

Optimization design for scramjet and analysis of its operation performance

Flow field numerical simulation methods of scramjet introduced in this paper, include using CFD method to analyze the flow phenomenon in each component of scramjet, i.e. forebody/inlet, combustor and afterbody/nozzle. Design and optimization of a generic scramjet model are investigated based on the bilevel integrated system synthesis method. Analysis and design procedures of each component are treated as a black box in scramjet system design. Components of scramjet are designed and optimized at subsystem level in the first step, and then a system level optimization is performed for the whole scramjet. Multi-fidelity simulation models are developed and applied to analyze and design the scramjet model. According to the requirement of design, appropriate fidelity simulation models are adopted in design cycle under the limitation of time and budget. A design and optimization example is presented in which some parameters are chosen as scramjet system level variables by sensitivity analysis of all possible design parameters; other parameters become component level variables of forebody/inlet, combustor and afterbody/nozzle. The design of experiment method and genetic algorithm arc applied to explore design space and to obtain optimal or near optimal solution. Operation performance of scramjet is also analyzed in this paper, considering the interaction between scramjet and vehicle airframe.

Numerical Simulation of Flow Field for a Whole Centrifugal Fan and Analysis of the Effects of Blade Inlet Angle and Impeller Gap

Numerical simulation of the flow field was carried out for a whole centrifugal fan to consider the interaction of three parts—inlet, impeller, and scroll. A modern optimum design method for a centrifugal fan has been presented using a computational fluid dynamics (CFD) technique to replace the conventional method. A sample fan based on the optimum design was manufactured and tested. The numerical prediction agrees well with the test data. The excellent performance of the sample fan has proved the validity of the method adopted. Moreover, the effects of the blade inlet angle and the gap between impeller and inlet on the fan performance are quantitatively analyzed. Particularly the energy loss in every passage, including the gap loss and the leakage flow rate in the gap, are discussed in detail in the paper. It is found that the blade inlet angle and the impeller gap play an important role for fan performance.

Numerical Simulation of Flow Field around Wind Turbine Blades Focused on Characteristics of Aerodynamics

Numerical Simulation of Flow Field around Wind Turbine Blades Focused on Characteristics of Aerodynamics

1209 熱ほふく流を伴う球状粒子周りの流れの数値解析(オーガナイズドセッション6-I 流れの複合現象:混相流,熱流体,流体関連振動)

1209 熱ほふく流を伴う球状粒子周りの流れの数値解析(オーガナイズドセッション6-I 流れの複合現象:混相流,熱流体,流体関連振動)

NUMERICAL SIMULATIONS ON THE HYDRODYNAMICS OF A TURBULENT SLOT JET IMPINGING ON A SEMICYLINDRICAL CONVEX SURFACE

This study presents the numerical simulations of flow characteristics of a turbulent slot jet impinging on a semicylindrical convex surface. The turbulent-governing equations are solved by a control-volume-based finite difference method with power-law scheme, and the well-known k − ϵ turbulence model associated with the wall function is used to describe the turbulent behavior and structure. While the width of the slot nozzle is fixed at 9.38 mm, the diameter of the semicylinder is at 150 mm, and air is the working medium, the adopted modifying parameters here include the Reynolds number of the inlet flow (Re = 6000 ˜ 20000), jet to impingement surface spacing (y / w = 7 ˜ 13), and the entrainment or wall boundary is employed nearby the convex surface. The numerical simulations of flow fields indicate that the velocity distribution of the free jet region departs from the center with increasing y / w. When we increase Reynolds number Re, the variation of the velocity on the convex surface becomes rapid, and the turbulent kinetic energy increases.