某型发动机短舱流动与换热的计算研究

某型发动机安装在直升机上,在进行地面悬停飞行试验中,发动机短舱后部温度超过限定值,为此,建立了该型发动机短舱流动和换热的计算模型,数值计算了发动机地面最大功率状态下短舱内部的流动和换热,结果表明,该状态下,短舱后部监测点温度超限.通过分析,提出两种短舱结构改进方案,计算后发现,短舱内部的流动和换热效果有了一定程度的改善,监测点温度低于规范要求的温度限定值,冷却效果很明显.提出的改进方案对工程实际具有一定的指导价值.     

Numerical solution of one-dimensional non-steady flow with supersonic and subsonic flows and heat transfer

The mesh method of solving one-dimensional non-steady subsonic flows is extended to cover supersonic flows and heat transfer. An algorithm is presented for the computation of the Riemann variables with friction, area change, heat transfer and entropy gradients.     

Transient heat transfer studies on a diesel engine valve

Numerical calculations based on finite difference approximations are carried out to assess the transient thermal response of the inlet and exhaust valves of a Tata-Mercedes, six cylinder, four stroke, water cooled diesel engine with a compression ratio of 19.5 and a rated power output of 110 hp at 3000 rpm for three different engine loadings. A detailed analysis has been given for estimating the boundary conditions of the inlet and exhaust valves of an internal combustion engine. The problem has been extended by applying a thin ceramic insulation coating of 2 mm thickness at the valve plate. The isothermal distribution in the valve bodies and the heat flow rates through the various cooling media for three different engine loadings have been depicted for each of the cases with and without insulation coating. The results indicate a reduction in heat loss through valves by use of an insulation coating on the valve plate.     

Improving utilisation of potential i.c. engine life by filtration

Neutron irradiation and radioisotope tracer techniques were used in wear tests on engines on test and on the road. Correlation between test life and road life was found to be related to environmental dust levels. Sensitive methods for measuring air-filter efficiency were developed. Air and oil filtration were found to profoundly affect engine wear-life and a new air inlet system was devised which also improved engine performance     

MHD copper-water nanofluid flow and heat transfer through convergent-divergent channel

This work is focused on the analytical solution of a nanofluid consisting of pure water with copper nanoparticle steady flow through convergent-divergent channel. The velocity and temperature distributions are determined by a novel method called Reconstruction of variational iteration method (RVIM). The effects of angle of the channel, Reynolds and Hartmann numbers on the nanofluid flow are then investigated. The influences of solid volume fraction and Eckert number upon the temperature distribution are discussed. Based on the achieved results, Nusselt number enhances with increment of solid volume fraction of nanoparticles, Reynolds and Eckert numbers. Also the fourth order Runge-Kutta method, which is one of the most relevant numerical techniques, is used to investigate the validity and accuracy of RVIM and good agreement is observed between the solutions obtained from RVIM and some known numerical results.

     

A study on the characteristivs of heat transfer in an engine piston

The piston temperature distribution with varying engine torque and speeds for a real engine operation has been determined by a numerical model. The model is developed by the finite element conduction method combined with engine simulation. In this model, the two boundary temperature concept instead of one constant boundary temperature was presented to approximate the ambient temperatures along the piston skirt. The two temperatures were first estimated, then adjusted by the iterated proces, for predicting piston temperatures, according to the energy balance of the whole engine energy system. In order to verify the predicted values, input data for cycle simulation were obtained, the piston temperatures were also measured. In this way the good agreement between the model and experimental results could be checked.     

Swirl flow post-CHF heat transfer with refrigerant 113

Heat transfer rate was experimentally determined in the post-CHF region of a steady-state two-phase flow of a refrigerant in a vertical tube with swirl induced by twisted-tape inserts. Experiments were performed with the vertical flow of refrigerant-113 in a tube with inside diameter of 7.75 mm, a heated length of 3.66 m and mass flux of 375–535 kg/m²s for swirl flow at a pressure of 0.184 MPa. Four tapes were used with twist-ratio of 2.5 to 9.2 for swirl flow. Liquid heating produced the low wall-superheat in the post-CHF region at steady-state, which is typical of heat exchanger operation. Superheated vapor measured at the test section exit in most tests ensured that entire post-CHF region was included. All refrigerant-113 data were compared with the data of water and refrigerant-12. The existing post-CHF heat transfer correlation of swirl flow was modified to predict the magnitude and trends of the data of the three fluids such as water, R-12 and R-113.     

Turbulent natural convection flow and heat transfer in an inclined square enclosure

Numerical analysis was performed for the two-dimensional turbulent natural convection in an inclined enclosure. The enclosure has two walls which one is heated and the other cooled, and has the other two walls of the linear temperature distributions. The inclined angle is equal to zero when the wall of linear temperature was horizontal and increases counter-clockwise. The mean continuity, mean momentum and mean energy equations have been obtained by using the conventional time-averaging procesure. The turbulent model has been applied ak-ε two equation model of turbulence similar to the one proposed by the Launder and Spalding. Numerical results were studied for a series of inclined angle, ranging from 0° to 60° and for a Grashof number range of 6×10⁶∼10⁸. The average heat transfer rate on hot wall is shown maximum value at 30° regardless of Grashof number taken here. When Gr≥5×10⁷ and θ≥45°, the flow region of whole enclosure became a significant turbulence. This paper was presented at the International Symposium on the Refined Flow Modeling and Turbulent Measurement. Iowa City, Iowa, U.S.A., 1985     

Development of a novel rotary flow control valve with an electronic actuator and a pressure compensator valve for a gas turbine engine fuel control system

This paper presents a new rotary proportional flow control valve with Cam-Nozzle configuration. The rotating cam against the fixed nozzle changes the flow area and then can meter the fuel flow. This valve equipped with a pressure compensator plunger type valve to retaining constant pressure difference across the flow control or metering valve. The cam shaft directly coupled to an electronic servomotor type rotary actuator and then it is possible to apply digital control techniques such as pulse width modulation (PWM) in this control system. This new valve configuration is developed for an electro hydro mechanical fuel control system in a gas turbine engine. In addition to aero engine application, this type of flow metering valve can widely be used in industrial hydraulic systems. In this unit, the output flow is proportional to the cam's angular position (or throttle command) and it is not sensitive to pressure fluctuations at nozzle inlet and outlet. The aim of this new design is to modify a manual single adjusted hydro-pneumatic fuel control unit to obtain a new electro-hydraulic fuel control system for a gas turbine engine. The main innovations in the presented fuel metering unit include new design of the rotary valve opening shape (Cam-Nozzle) without metal to metal contact, use of a rotary electronic actuating mechanism and also direct coupling between the actuator and the rotating cam. The increased fuel metering precision in the new flow control valve has improved the ultimate control accuracy of system. A computer simulation software based on the proposed model, is performed to predict the steady state and transient performance and to analyze effect of important design parameters on valve outlet fuel flow and obtain the final design parameters. The validity of the proposed valve configuration is assessed experimentally in the steady state and transient modes of operation. The results show good agreement between simulation and experimental in both modes (max. 4% deviation).     

Effects of combustor-level high inlet turbulence on the endwall flow and heat/mass transfer of a high-turning turbine rotor cascade

Experimental data are presented which describe the effects of a combustor-level high free-stream turbulence on the near-wall flow structure and heat/mass transfer on the endwall of a linear high-turning turbine rotor cascade. The endwall flow structure is visualized by employing the partial- and total-coverage oil-film technique, and heat/mass transfer rate is measured by the naphthalene sublimation method. A turbulence generator is designed to provide a highly-turbulent flow which has free-stream turbulence intensity and integral length scale of 14.7% and 80mm, respectively, at the cascade entrance. The surface flow visualizations show that the high free-stream turbulence has little effect on the attachment line, but alters the separation line noticeably. Under high free-stream turbulence, the incoming near-wall flow upstream of the adjacent separation lines collides more obliquely with the suction surface. A weaker lift-up force arising from this more oblique collision results in the narrower suction-side corner vortex area in the high turbulence case. The high free-stream turbulence enhances the heat/mass transfer in the central area of the turbine passage, but only a slight augmentation is found in the endwall regions adjacent to the leading and trailing edges. Therefore, the high free-stream turbulence makes the endwall heat load more uniform. It is also observed that the heat/mass transfers along the locus of the pressure-side leg of the leading-edge horseshoe vortex and along the suctionside corner are influenced most strongly by the high free-stream turbulence. In this study, the endwall surface is classified into seven different regions based on the local heat/mass transfer distribution, and the effects of the high free-stream turbulence on the local heat/mass transfer in each region are discussed in detail.     

An experimental study on the flow and heat transfer characteristics of an impinging jet

The flow and heat transfer characteristics of an impinging jet is investigated in two major stages. The first stage is about the investigation of the three dimensional mean flow and the turbulent flow quantities in free jet, stagnation and wall jet region. After a complete documentation of the flow field, the convective heat transfer coefficient distributions on the impingement plate are presented, during the second stage of the study. Heat transfer experiments using the new hue-capturing technique result in high resolution wall heating rate distributions. The technique is fully automated using a true color image processing system. The present heat transfer results are discussed in detail in terms of the flow characteristics. The measurements from the new method are compared with conventional heat flux sensors located on the same model. These heat transfer distributions are also compared with other studies available from the literature. The new non-intrusive heat transfer method is highly effective in obtaining high resolution heat transfer maps with good accuracy.     

Characteristics of fluid flow and heat transfer in a fluidized heat exchanger with circulating solid particles

The commercial viability of heat exchanger is mainly dependent on its long-term fouling characteristic because the fouling increases the pressure loss and degrades the thermal performance of a heat exchanger. An experimental study was performed to investigate the characteristics of fluid flow and heat transfer in a fluidized bed heat exchanger with circulating various solid particles. The present work showed that the higher densities of particles had higher drag force coefficients, and the increases in heat transfer were in the order of sand, copper, steel, aluminum, and glass below Reynolds number of 5,000.     

Cycle resolved no emissions and its relation with combustion chamber pressure in an s.i. engine with fast response no analyzer

A fast response NO analyzer was applied to investigate the relation between cycle-by-cycle NO emissions and combustion chamber pressure. NO emissions were sampled at an isolated exhaust manifold of 4-stroke spark ignition engine to avoid the interference of exhaust gas from other cylinders. The linear correlation analysis was performed with collected data of NO emissions and combustion chamber pressure with respect to the various air-fuel mixture ratios and engine loads. The sampled data sets were obtained during 200 cycles at each operating condition. The results showed that there was a typical pattern in NO emissions from an exhaust port through a cycle. It was possible to set a block of crank angle in which the linear correlation coefficient between NO emissions and combustion chamber pressure was high. As the engine load increased, NO emissions were more dependent on combustion chamber pressure after TDC. It was also analyzed that the correlation between two parameters with respect to air-fuel mixture ratio tended to increase as mixture went leaner. Furthermore, this correlation coefficient for the mixture near the lean limit seemed to be kept high even though combustion was unstable.     

Effects of particle entrainment on heat transfer past particles in an oscillating flow

In order to investigate the effect of the particle entrainment on the heat transfer past paricles entrained in an oscillating flow with and without a steady velcoity, the two dimensional, unsteady, laminar conservation equations for mass, momentum and energy transport in the gas phase are solved numerically in spherical coordinates. The particle momentum equation is also solved simultaneously with the gas phase equations. The numerical solution gives the particle velocity variation as well as the gas phase velocity and temperature distribution as a function of time. The local and space-averaged Nusseit number with particle entrainment is compared with that without particle entrainment. In the case of an oscillating flow with a steady velocity, the values of the space-averaged Nusselt number with particle entrainment are lower than those without particle entrainment at frequencies of 50 and 2000 Hz since the moving particle is entrained in the steady velocity. In the case of an oscillating flow without a steady velocity, the space-averaged Nusselt number with entrainment at a frequency of 50 Hz is slightly lower than that without particle entrainment, with a phase lag. At 2000 Hz, the space-averaged Nusselt number with and without particle entrainment is almost the same, due to very small particle entrainment.     

Nanofluid thin film flow and heat transfer over an unsteady stretching elastic sheet by LSM

This study is carried out on the unsteady flow and heat transfer of a nanofluid in a stretching flat plate. Least square method is implemented for solving the governing equations. It also attempts to demonstrate the accuracy of the aforementioned method compared with a numerical one, Runge-Kutta fourth order. Furthermore, the impact of some physical parameters like unsteadiness parameter (S), Prandtl number (Pr) and the nanoparticles volume fraction (?) on the temperature and velocity profiles is scrutinized carefully. Accordingly, the results obtained from this study reveal that the temperature enhances by means of augmenting the nanoparticles volume fraction. At η ∈ {0, 0.5}, the velocity decreases as a result of a rise in nanoparticles volume fraction and at η ∈ {0.5, 1}, an opposite treatment takes place. Moreover, velocity distribution augments by raising the S value, however an inverse trend is observed in temperature values. Moreover, the local skin friction coefficient indicated a notable rise by increasing the S parameter as well as a steady decrease by rising ?. Finally, water-Alumina nanofluid demonstrated better heat transfer enhancement compared to other types of nanofluids.     

折流板换热器壳程流体流动与传热特性数值模拟

根据流体动力学和计算传热学理论,建立了折流板管壳式换热器计算模型,运用CFD技术对换热器壳程流体的流动与传热问题进行了三维数值模拟,得到了不同壳程进口雷诺数Re条件下换热器壳程流体的流场和温度场。对数值模拟结果进行分析,以总传热系数h,壳程总压降Δp以及单位压力损失下的传热系数h/Δp作为换热器性能的衡量标准,分析了不同折流板间距和不同折流板圆缺高度时管壳式换热器壳程总传热系数h、总压降Δp以及h/Δp随壳程进口雷诺数的变化规律。结果表明:随着壳程进口流速的增大,换热器壳程总传热系数和总压降增大、h/Δp减小;在壳程流体流量不变的情况下,结合单位压力损失下的传热系数h/Δp,适当减小折流板间距或减小折流板圆缺高度,可提高换热器的换热性能。     

典型波纹翅片单元流动与传热特性的数值研究

以两种典型的波纹翅片单元为研究对象,在合理简化条件下给出了物理模型和数学模型,通过流固界面的传热耦合,对不同进口风速下波纹翅片单元的流动及传热和阻力特性进行了数值研究.通过对传热系数,Nu数、压降以及涡量分布的对比分析,结果表明:人字形翅片的传热性能优于波浪形翅片,而流动阻力性能却没有明显的劣势,其主要原因是翅片流场中涡流的产生与耗散存在差异.     

Prediction of turbulent heat transfer in swirling flow downstream of an abrupt pipe expansion

Turbulent heat transfer characteristics in swirling flows downstream of an abrupt pipe expansion with a diameter ratio of 0.5 are predicted by full Reynolds stress model. The uniform heat flux condition is imposed on the downstream wall. The flows with weak and strong swirls as well as without swirl are computed. The governing differential equations are discretized by finite volume method. Results show that the Reynolds stress model predicts accurately the maximum local Nusselt number for the case with strong swirl, but that the effects of swirl are not fully accounted for the case with weak swirl.     

Burnett simulations of gas flow and heat transfer in microchannels

In micro- and nanoscale gas flows, the flow falls into the transition flow regime. There are not enough molecule collisions and the gas deviates from the equilibrium. The Navier-Stokes equations fail to describe the gas flow in this regime. The direct simulation Monte Carlo method converges slowly and requires lots of computational time. As a result, the high-order Burnett equations are used to study the gas flow and heat transfer characteristics in micro- and nanoscale gas flows in this paper. The Burnett equations are first reviewed, and the augmented Burnett equations with high-order slip boundary conditions are then used to model the gas flow and heat transfer in Couette and Poiseuille flows in the transition regime.