Generally, it has two different ways for fuel transfer for areoplane, the simplest one is by gravity, and another is by pumps. But the simplest one mighte change to the vital method in some situation, such as electrical and mechanical accident. So the study of gravity feed oil is aslo important. Past calculations assumed that, under gravity feed, only one fuel tank in aircraft supplies the fuel needed for preventing extremely serious accident to happen. Actually, gravity feed oil is a transient process, all fuel tanks compete for supplying oil and there must have several fuel tanks offering oil simultaneously The key problems to calculate gravity feed oil are the sumulation of the multiple-branch and transienl process. Firstly, we presented mathematical models for oil flow through pipes, non-working pupms and check valves, ect. Secondly, On the basis of flow network theory and time difference method, w(, established a new calculation method for gravity feed oil of aeroplane fuel system. This model can solve the multiple-branch and transient process simulation of gravity feed oil. Our method takes into consideration all fuel tanks and therefore, we believe, our method is intrinsically superior to traditional methods and is closer to understanding the real seriousness of the oil supply situation. Finally, we give a numerical example using the new method for a certain type of aircraft under gravity feed . achieved the variations of oil level and flow mass per second of each oil tanks which showed in Figures below. These variations show preliminarily that our proposed method of calculations is satisfactory.

This paper presents a numerical model of internal flows on lubricant supplying and scavenging flow path of an aero-engine lubrication system. The numerical model was built in the General Analysis Software of Aero-engine Lubrication System (GASLS), developed by Northwestern Polytechnical University. The lubricant flow flux, pressure and temperature distribution at steady state were calculated. GASLS is a general purpose computer program employed a 1D steady state network algorithm for analyzing flowrates, pressures and temperatures in a complex flow network. All kinds of aero-engine lubrication systems can be divided into finite correlative typical elements and nodes from which th,~ calculation network is developed in GASLS. Special emphasis is put on how to use combinational elements which is a type of typical elements to replace some complex components such as bearing compartments, accessory drive gearboxes or heat exchangers. This method can reduce network complexity and improve calculation efficiency. The computational results show good agreement with experimental data.

A computational study of the flow characteristics inside a diffusive S-duct inlet with and without vortex generators (VGs) is conducted. The primary discussion herein is focused on the development of secondary flow in the S-duct, pressure recovery and distortion at the exit for the S-duct with and without VGs. The S-duct has a cross-sectional area change from a retangular at the entrance to a full circle at the exit. Full three-dimensional Navier-Stokes equations are solved using finite volume method and ~-c turbulence model is employed. In order to validate the numerical methods, the predicted results of surface pressure are compared with flight test for S-duct without VGs. And it shows fairly good agreement. The CFD computed flows in the S-duct and out of the S-duct inlet are carefully examined. Cross-sectional area change or curvature of the duct centerline lead to streamline curvature. The cross stream pressure gradients resulting from steamline curvature induce significant secondary flow. It is a dominant feature for S-duct. Six cross-sectional planes reveal the development of secondary flow in the S-duct with and without VGs. The different secondary flow developing progresses between S-duct with and without VGs are discussed. A large pair of counter-rotating vortices caused by secondary flow is at the exit for the S-duct without VGs. Low momentum fluid of the boundary layer are convected to the center of the duct. High momentum and low momentum fluid is blended downstream, so that both the uniformity and magnitude of the total pressure profile are degraded. Performance of the S-duct with two different location VGs is assessed by calculating total pressure recovery and distortion, and comparing them to the values for the S-duct without VGs. Through the comparison, it shows that the installation of VGs in the S-duct inlet at two different locations is helpful for decreasing distortion and swirl, but it is ineffective in improving the pressure recovery. Counter-rotating vortices are weakened to different extent at the exit in the S-duct with two different location VGs.