Numerical Study Of The Fan Flow Under Low Reynolds Number

The improvement of aeroplane performance has made a greater demand on the propulsor. Fan/compressor is a primary component of the propulsor and often become the main reason of the failure of model development due to its high technology and designing difficulty. What negative effect will occur on the fan/compressor which is designed to run on the ground when it is placed in condition of higher altitude and reynolds number. How can we eliminate the negative effect and improve the performance of the fan by using the advanced blade technology? The answer is what we are going to find out.Firstly, the paper analyzes the internal flow and the aerodynamic performance of the fan in the condition of low reynolds number and ground level, and investigate the influence of the decrease of reynolds number on the performance of fans, obtaining the flow feature of the fan in condition of low reynolds number. When reynolds number is below the critical reynolds number, the performance of the fan will worsen with the decrease of reynolds number, i.e. the flow rate decline; the efficiency decreased and the pressure ratio in surge point decreased. The reason is that in condition of low reynolds number, the boundary layer on the surface of the blade becomes thicker and the flow regime in the boundary layer changes from turbulence into laminar flow resulting in a larger separation size because the laminar flow is less resistable against separation. The shock-loss and the wake-loss induced by the shock increase. The flow in the end-wall zone deteriorates and the end wall loss increases. The off-design performance of the fan is impaired because a separation bubble tends to exist on the leading edge of the blade when the angle of attack is changed.At present, as a means of controlling the end-wall loss, the bowed blade technology has been widely used in the compressor. In this paper, some type of compressor blade is retrofitted to investigate the influence of the curve of blade on the performance of compressor. The comparative analysis between straight and bowed blades shows that bowed blade can strengthen radial secondary flow and weaken traverse secondary flow and both of these two effects can lower end-wall loss. For the fan investigated in this paper, the 20°positive bowed blade has the best performance.