某型发动机尾喷管特性确定方法

获取发动机尾喷管特性是飞行推力确定的重要环节。通过对尾喷管特性物理意义的分析,提出了采用CFD数值仿真与地面全机校准试验相结合的尾喷管特性确定方法,以该方法获取的尾喷管特性为基础,在高空台试验中采用燃气发生器法计算发动机进口空气流量和出口总推力,并与高空台实测值进行对比,在所有功率状态下计算值与实测值的最大相对误差不超过5%,表明该方法确定的尾喷管特性满足飞行推力确定的精度要求,证明了该方法合理有效。     

Lubricant flow through the nozzle of a drawing die

Lubricant flow through the nozzle of a drawing die, governed by the power-law rheological equation of state, is examined. The nozzle dimensions, ensuring a maximum lubricant throughput, are obtained analytically by using the variation methods. A study is undertaken of the effects of the rheological equation exponent and piezocoefficient on the film thickness, heat generation and pressure distribution over the nozzle length.     

Pressure mode decomposition analysis of the flow past a cross-flow oscillating circular cylinder

Journal of Mechanical Science and Technology - Proper orthogonal decomposition (POD) is often employed in developing reduced-order models (ROM) in fluid flows for design, control, and optimization....     

某型发动机涡轮导向叶片故障探讨

针对某型发动机涡轮导向叶片故障作进行了详细的分析，并推测了产生的原因，并据此提出了改进的设想和使用维护中应注意的问题。     

The humidity effect on air flow rates in a critical flow venturi nozzle

A Critical Flow Venturi Nozzle (CFVN) is usually calibrated using dry air. Yet CFVNs in industrial and calibration service centers are often used to measure flow rates of humid air. Therefore, ISO 9300 provides the calculation method for the humidity effect on discharge coefficients of CFVN. However, since this method is only due to a theoretical analysis, it is important to confirm and check the ISO calculation method for the humidity effect on CFVN with its isentropic analysis by means of an experimental method.In this experiment, three CFVNs with diameters of 0.4, 0.8 and 1.6 mm were calibrated with dry air (with the dew point −40 °C), in a primary air flow standard system with a mercury sealed piston prover, installed at the Korea Research Institute of Standards and Science (KRISS). Another piston prover, a portable dry piston prover, was used as a reference meter and was also calibrated in the primary standard system using dry air. The repeatability of this dry piston prover was confirmed with the deviation being less than 0.05%. The CFVNs were tested with this dry piston prover, using humid air. For air types with high humidity, the humidity effect on flow rates through the CFVNs showed quite significant difference between the experimental results and those from the ISO method with isentropic analysis. But for air types with low humidity, its effect was relatively insignificant.     

电火花修复涡轮导向叶片试验研究

研究了电火花修复K418涡轮导向叶片,为涡轮导向叶片的修复提供了理论依据.通过观察试样金相组织及测量显微硬度,并对所得试验数据进行分析,得出结论:修复后试样的金相组织较修复前均匀,晶粒明显细化;修复后试样硬度值一般提高30～50 HV,可以推断试样的耐磨性将会得到改善;最优工艺参数为电压65V,功率B2,频率C1,最大影响因素为电压;修复中还存在气孔、裂纹等缺陷,可以通过进一步试验,比如对试样进行预热、缓冷、改变材料成分等加以避免.     

Research on the dynamic characteristics of a turbine flow meter

In the hardware-in-loop simulation of aero-engine control system where the real fuel regulator is engaged, it's crucial to measure the real-time flow rate. In view of this, a flow meter with high precision and fast response is important. In this paper, modeling and experiments are conducted to verify the dynamic characteristics of a turbine flow meter (TFM). For the modeling part, driving torque and resistance torques are analyzed to derive the kinetic equation of TFM. Simulation with the kinetic equation shows good dynamic performance of TFM. In experiments, a workbench is designed to generate step-type flow and sine-type flow for identification in time domain and frequency domain. Results show that the settling time for TFM is no more than 100 ms and its band-with is over 4.61 Hz. Compared with the settling time of a main fuel valve and the band-width of a main fuel control loop, that is, 1.2 s and 2 Hz respectively, TFM is considered to be adaptive to measure the fuel of aero-engine.     

A study on the flow with nonequilibrium condensation in a minimum length nozzle

As recognized previously, a minimum-length nozzle has the smallest possible throat-to-exit length that is still capable of maintaining uniform supersonic flow at the nozzle exit. In the present study, for the flow of moist air through a nearly minimum-length nozzle designed by the method of characteristics, the effects of nonequilibrium condensation on the uniformity of flow properties, the momentum efflux, and the flow distortion at the nozzle exit plane are discussed by experiment and numerical analysis of a third-order Total Variation Diminishing (TVD) finite difference scheme. The onset and zone of nonequilibrium condensation in a minimum-length nozzle are quite different from those of a general convergent-divergent supersonic nozzle. We know that the uniformity of flow properties at the nozzle exit with regard to the flow with nonequilibrium condensation in a minimum-length nozzle cannot be guaranteed. On the other hand, owing to the positions of the onset of condensation at the incident region of expansion waves from the sharp corner just downstream of the nozzle throat, the deceleration gradient and magnitude of heat released from the process of nonequilibrium condensation to the surrounding of ϕ₀=60% are greater than those of ϕ₀=70% in the case of T₀=290K. Furthermore, it has been determined that the decrease in efflux of momentum from the nozzle exit for the stagnation relative humidity of ϕ₀=70%(T₀=290K), which corresponds to the case with nonequilibrium condensation shock, is 6.8% smaller than that of isentropic expansion. This paper was recommended for publication in revised form by Associate Editor Do Hyung Lee Soon-Bum Kwon received his B.S. and M.S. degrees in Mechanical Engineering from Kyungpook National University in 1974 and 1980, respectively, and his Ph.D. degree from Kyushu University in 1987. He is a Professor at the School of Mechanical Engineering at Kyungpook National University. His research interests are compressible gas dynamics and nonequilibrium condensation.     

Computational/experimental study of a variable critical nozzle flow

Recently, critical nozzles have been extensively utilized to measure the mass flow rate in a variety of industrial applications. For the measurement of the mass flow rates in a wide range of operation conditions, the critical nozzle is required to be designed with different diameters. The objective of the present study is to investigate the effectiveness of a variable critical nozzle. A rod with a small diameter is inserted into the critical nozzle to change the effective cross-sectional area of the critical nozzle. Experimental work is performed to measure the mass flow rate of the critical nozzle with rod. Computational work is carried out using the two-dimensional, axisymmetric, compressible Navier–Stokes equations which are discretized using a fully implicit finite volume method. The diameter of the rod is varied to obtain different mass flow rates through the variable critical nozzle. Computational results predict well the measured mass flow rates. The boundary layer displacement and momentum thickness at the throat of the critical nozzle are given as a function of Reynolds number. The discharge coefficient of the critical nozzle is given as an empirical equation.     

Numerically analyzed supersonic flow structure behind the exit of a two-dimensional micro nozzle

The compressible flow field is numerically analyzed in a two-dimensional converging-diverging nozzle of which the area ratio, exit to throat, is 1.8. The solver is FLUENT and the embedded RNG k − ε model is adopted to simulate turbulent flow. The plume characteristics such as shock-cell structure are discussed when nozzle pressure ratio and stagnation temperature at the nozzle entrance are varied. The downstream flow field can be classified into two types based on the shock shapes generated near the nozzle exit. First, a reiterative pattern in the plume is not formed between the slip streams in case that a strong lambda-type shock wave exists. Second, when oblique shock waves are crossing each other on the nozzle centerline, a shock cell structure appears in the plume field. Even when the flow field is changed due to stagnation temperature, the upstream of the shock wave is little affected. Especially, the pressure distributions on the nozzle centerline behind the shock wave are rarely influenced by the stagnation temperature, that is, the product of density and temperature is nearly constant provided that the working fluid is a perfect gas. Therefore, the pressure field shows quasi-isobaric behavior far downstream.     

Response and flow characteristics of a dual-rotor turbine flowmeter

The technical problems of flow measurement in hypersonic flight could be mitigated through dual-rotor turbine flowmeters (DRT-FMs). In this study, a visual experiment platform was designed to reproduce the flow of a 1.3 cm diameter DRT-FM. A mathematical model considering two rotors was developed to perform a parameterised study and evaluate the rotor responses. Further, the entire flow passage was numerically simulated through an added automatic iterative rotor-dynamic calculation based on the angular momentum balance theory. According to the experimental results, the response range of the rotational speeds was divided into three stages: unresponsive, unstable, and stable. The downstream rotor responded at a lower flow rate, increasing the measurement range of the rotor turbine flowmeter. Considering the region of linear increase in the rotor speed in stable state under different flow media, tip clearances, and number of blades, the mathematical results indicated that the downstream rotor exhibited a compensation effect of the rotational speed on the calculation of rotational speed at the current flow rate conditions, which mitigates the measurement instability of the upstream rotor. Through the simulations, the rotation speed difference of the two rotors resulted in a slight periodic disturbance to the downstream rotor, which was alleviated after flowing through the spacer and could be ignored. Moreover, the high vorticity regions appeared around the rotors and areas of abrupt structural changes in the flow passage; the distribution gradually extended as the vorticity decreased. The present study provides an understanding of the DRT-FM and some recommendations to improve its characteristics.     

Flow structure in critical flow Venturi nozzle and its effect on the flow rate

The flow fields in toroidal Venturi-nozzles, shaped according to the ISO-9300 Standard, have been investigated using numerical flow simulation. The present study was aimed at clarifying some of the phenomena associated with unchoking the flow in the throat. To this end, the shock structure has been studied for different Reynolds numbers and exit pressure ratios. The flow simulations were carried out in two and three dimensions. The flow fields were always unsteady, displaying a complex shock–boundary layer interaction.     

某型发动机非加力情况下收-扩尾喷管流动特性研究

针对某型涡扇发动机的收-扩尾喷管模型在加力不接通试验工况下的流动特性,通过建立模型,进行相关的数值计算研究,获得了不同喉道面积、面积比和尾喷管落压比条件下的收-扩尾喷管模型的流量系数和推力系数数据及其变化规律,为发动机地面台架标定试验和飞行试验中发动机进口空气流量和标准净推力的确定提供了基础数据。     

跨声速涡轮级三维流场的数值模拟

采用FLUENT软件对某变循环发动机的高压跨声速涡轮级的三维粘性流场进行了数值模拟计算,使用混合平面法实现涡轮级动、静三维流场联算,计算中分别采用两个典型的双方程模型RNGk-ε模型和realizable k-ε模型,并将计算结果进行了对比,结果在一定程度上表明在分离流计算和带二次流的复杂流动计算中,Realizable k-ε模型的计算结果更精细一些.同时分析了其内部流场以及通道内总压损失的分布情况,为进一步改进叶型设计提供了理论依据.     

Three-dimensional Doppler Global Velocimetry in the flow of a fuel spray nozzle and in the wake region of a car

A Doppler Global Velocimetry system optimised for time averaged three component velocity measurements was designed and set-up. The first application of the system was the investigation of the flow field of a swirl spray nozzle in a cylindrical casing. Because of the axial symmetry of the mechanical set-up it was possible to measure the planar distribution of all three velocity components of the highly three-dimensional flow with just one optical arrangement. The flow field in the whole volume of the combustor was measured in only 10 min. This is extremely fast and demonstrates the most important property of the new system.The DGV system was also applied to investigate the wake region of a car model in a wind tunnel. An arrangement with three light sheets was chosen. The 3D-DGV results are in good agreement with 3D-LDA measurements of the same flow.     

Numerical investigation of cross-flow around a circular cylinder at a low-reynolds number flow under an electromagnetic force

The effect of the electromagnetic force (or Lorentz force) on the flow behavior around a circular cylinder is investigated by computation. Two-dimensional unsteady flow computation forR _e =10² is carried out using a numerical method of finite difference approximation in a curvilinear body-fitted coordinate system by solving the momentum equations including the Lorentz force as a body force. The effect of spatial variations of the Lorentz forcing region and forcing direction along the cylinder circumference is investigated. The numerical results show that the Lorentz force can effectively suppress the flow separation and oscillation of the lift force of circular cylinder cross-flow, leading to reduction of drag.     

非均匀来流对涡轮流场的影响

涡轮机械的非均匀进口来流会使得涡轮的流场不均匀,从而影响涡轮的工作性能。本文根据涡轮的工作机理,建立了存在叶尖间隙的涡轮流动模型,考虑来流的周向非均匀性,研究了涡轮流场的变化规律,讨论了不同来流参数对涡轮流场参数的影响。     

喷嘴雾化流场数值仿真及结构改进研究

针对空气喷嘴形状对雾化性能影响的问题,对不同扇面结构参数下的空气喷嘴的雾化性能进行了研究,对空气喷嘴结构参数与雾化流场之间的规律进行了归纳,提出了一种空气喷嘴的结构模型,基于雷诺N-S方程与标准K-ε湍流模型以及标准壁面函数法,采用CFD方法对不同扇面孔数量及不同扇面锥角下的空气喷嘴的雾化性能进行了数值仿真,分析了空气喷嘴不同扇面参数的改变对雾化性能的影响,并通过搭建喷枪台架实验,对优选的结构模型进行了实验验证。研究结果表明,仿真结果与实验数据基本符合要求,改进后的空气喷嘴雾化性能得到了改善,为今后空气喷嘴结构的优化设计提供了一定的参考。     

基于稳定流量可调式拉伐尔管的压力临界比研究

对气力输送系统设计的可调式拉伐尔管的压力临界比进行了数值模拟和试验验证,试验结果和数值模拟结果一致,表明可调式拉伐尔管的工作状态完全处于临界状态下,可以起到稳流的作用。并提出了下一步的研究重点。