An Application of 3-D Numerical Simulation on Control Unit of Gasturbine Engine

Abstract

Numerical simulation of the kerosene in a high pressure centrifugal pump was conducted based on viscous N-S equations and multiphase flow. The cause, location and initiation factors of cavitations were investigated. Actual conditions of centrifugal pump were introduced into the numerical simulation. It shows that the simulation results are in good accordance with the actual damage to centrifugal pump by cavitations. Due to its advantages of large flow, simple structure, lightweight, high reliability, strong anti-dirty ability, centrifugal pump has been widely used in the aviation fuel systems. However, certain problems such as high temperature in small flow condition, great pressure swing and cavitations erosion, are also found during its working process, with the working time increase, cavitations' erosion to the pump's material also increases. When the cavitations continue to develop, a sudden drop in performance of pump will appear, accompanied with noise and vibration, and even resulted in abnormal working situation of the centrifugal pump (1). Traditional design principle of centrifugal pump is based on Lorenz flow theory invented in early 20th century, which means relatively backward design, no accurate analysis and simulations conducted for the vortex flow phenomena inside the pump's impeller and the shell in the design process. The fact is that the flow inside the centrifugal pump is a complex three-dimensional turbulent flow, the flows of the situation are affected by pump's shell shape of the cavity, the impeller bending curvature, pump rotational speed and the import and drainage of the pumps(2) (3). As a result, it is especially important now to use advanced modern simulation and analysis techniques to improve the traditional design methods of the centrifugal pump design, even to improve the pump's performance. First of all, geometric modeling of centrifugal pump is conducted in this paper. Then a two-phase flow model is established for some necessary parts of the three-dimensional physical model. Simulations of the kerosene flow inside the impeller passage are conducted for nearly all working conditions. Pressure distributions on the shell's inner wall and impeller, and flow characteristics of kerosene in the pump for different pressures and flow rates are systematically simulated, and the flow fields to the cavitations erosion influences and control ways are also discussed. II. CONTROL EQUATIONS Cavitations are induced from the flow rates, pressures, temperatures and other factors when centrifugal pump in different working conditions impacted on the centrifugal pump. To investigate the formation and the disappearing of the cavitations, it is necessary to simulate the flow of vapor-liquid phases inside the casing and impeller passages and to investigate the processes of the impingement of liquid to the metal surface due to the bubble formation and collapse. Let the coordinates (x, y, z) as the reference system. The z- axis coincides with the impeller shaft, and the impeller rotates around the z-axis with angular velocity ω. The fluid was imported into the impeller from an inlet with radius R1, flows through the passage separated by the impeller's blades and leaves the impeller through an outlet with radius R2. Governing equations are Reynolds time-averaged N-S equation considering viscosity: