Computational Analysis of Mixing Guide Vane Effects on Performance of the Supersonic Ejector-Diffuser System

The flow field in the ejector-diffuser system and its optimal operation condition are hardly complicated due to the complicated turbulent mixing, compressibility effects and even flow unsteadiness which are generated inside the ejector- diffuser system. This paper aims at the improvement in ejector-diffuser system by focusing attention on entrainment ratio and pressure recovery. Several mixing guide vanes were installed at the inlet of the secondary stream for the purpose of the performance improvement of the ejector system. A Computational Fluid Dynamics (CFD) method based on Fluent has been applied to simulate the supersonic flows and shock waves inside the ejector. A finite volume scheme and density-based solver with coupled scheme were applied in the computational process. Standard k-ω turbulent model, implicit formulations were used considering the accuracy and stability. Previous experimental results showed that more flow vortexes were generated and more vertical flow was introduced into the stream under a mixing guide vane influence. Besides these effects on the secondary stream, the mixing guide vane effects on the shock system of the primary stream were also investigated in this paper. Optimal analysis results of the mixing guide vane effects were also carried out in detail in terms of the positions, lengths and numbers to achieve the best operation condition. The comparison of ejector performance with and without the mixing guide vane was obtained. The ejector-diffuser system performance is discussed in terms of the entrainment ratio, pressure recovery as well as total pressure loss.

Analysis of choked two-phase flows of gas and particle in a C-D nozzle

Particle-gas two-phase flows show significantly different behaviors compared to single gas flow through a convergent-divergent nozzle. Non-equilibrium effects, thermal and velocity lag results to the inefficiency of nozzle performance. In the present studies, theoretical analysis and numerical simulations were carried out to investigate particle-gas flows in a C-D nozzle. Homogeneous equilibrium model that no lag in velocity and temperature occurs between particles and gas phase was used to derive mass flow rate and sound speed of multiphase flows. Two-phase flows are regarded as isentropic flows that isentropic relations can be used for homogeneous equilibrium model. Discrete phase model （DPM） where interaction with continuous phase and discrete random walk model were considered was used to calculate particle- gas flows. Particle mass loadings were varied to investigate their effects on choking phenomena of particle-gas flows. Mass flow rate and sound speed of mixture flows were theoretically calculated by homogeneous equilibrium model and compared with numerical results. Shock wave structure and particle number density were also obtained to be different at different particle mass loading and operating pressure conditions.

A Computational Study of the Gas-Solid Suspension Flow through a Supersonic Nozzle

The present study focuses on numerical simulation of the gas-solid suspension flow in a supersonic nozzle. The Euler- Lagrange approach using a Discrete Phase Model (DPM) has been used to solve the compressible Navier-Stokes equa- tions. A fully implicit finite volume scheme has been employed to discretize the governing equations. Based upon the present CFD results, the particle loading effect on gas-solid suspension flow was investigated. The results show that the presence of particles has a big influence on the gas phase behavior. The structure of shock train, the separation point, and the vortex of the backflow are all related to particle loading. As the particle loading increases the flow characteris- tics behave differently such as 1) the strength of shock train decreases, 2) the separation point moves toward the nozzle exit, 3) the number and strength of vortex increase, 4) the strength of first shock also increases while the other pseudo shocks decreases. The change of gas flow behavior in turn affects the particle distribution. The particles are concen- trated at the shear layers separated from the upper wall surface.

Flow Fields with Vortex in a Small Semi-open Axial Fan

In order to clarify the effect of tip clearance (TC) size on fan performance and the flow field at rotor outlet in asmall semi-open axial fan, the experimental investigation was carried out. The tip diameter of test fan rotor was180mm and test TC sizes were lmm (TC=1mm) and 4mm (TC=4mm). Fan characteristics tests were carried outfor two cases of TC size and three-dimensional velocity fields at rotor outlet were measured using a single slanthot-wire probe at four flow-rate conditions. As a result, it was found that the pressure - flow-rate characteristicscurves for two cases showed almost the same tendency. However, the ensemble averaged velocity profiles alongradial measurement stations of TC=4mm largely changed compared with that of TC=lmm in cases of smallflow-rate condition. From the phase-locked averaging results, it was also found that the vortex existed in the rotoroutlet flow field of high flow-rate condition for each TC case. Compared with the vortices for TC=1mm andTC=4mm, the vortex for TC=4mm was stronger than that for TC=1mm.

Flow Fields with Tip Leakage Vortex in a Small Axial Cooling Fan

为了改进扇子特征，特别效率和噪音，与一个大尖端清理一把小轴的冷却扇子铺平，有尖端漏旋涡的内部流动大小用一根我类型热电线的探针在扇子转子插头被执行。探查被设为向二个方向，平行和正常测试扇子的南方的飞机，并且二个方向性的速度部件被测量。从扇子测试的结果，测试扇子没在它的压力上与一个积极坡度有不稳定的特征，这被发现—流动率曲线。从速度测量的结果，尖端漏旋涡在最大的效率流动率和大流动率条件退出了，这被观察。然而，以小流动率条件，尖端漏旋涡没被观察，流动地被扩大向。