ICCES, vol.14, no.1, pp.1-22
Improving of the micro-turbine’s centrifugal impeller performance by changing the blade angles
R. A. Tough1,2 , A. M. Tousi2 , J. Ghaffari2
In this paper, micro-turbine centrifugal impeller with three different blade angles was investigated by using Computational Fluid Dynamics (CFD) method. The other basic geometric parameters are held constant. The inﬂuence of the blade angles change on the observed values was determined from numerical solution of the ﬂow in the impeller with help of the FLUENT software. The numerical simulation focused on the air ﬂow from compressor impeller inlet to exit, and the performance of impeller is predicted. The numerical solution was performed for original impeller geometry and for two other cases, in which blade inlet angle and backward sweep was changed. The standard k − ε turbulence model was used to obtain the eddy viscosity. Performance of the code was veriﬁed using measured data for the
Keywords: micro-turbine centrifugal compressor, CFD, blade inlet angle, backward sweep
Microturbines are gas turbines with a power ranging approximately from 10 to 200 kW. These devices can be used in stationary, transport or auxiliary power applications. In a micro-turbine, a centrifugal compressor compresses the inlet air and a radial turbine change the hot gas kinetic energy to the rotary work. Both turbomachinery components are radial. Micro-turbine compressors have been widely accepted as effective devices to improve the performance of these engines. The ﬂow through the centrifugal compressor is complex due to growth of boundary layers and ﬂow separation on blade surfaces, the formation of secondary ﬂows due to rotation and passage curvature and tip leakage in the impeller region. Resulting jet-wake formation is associated with high viscous losses and affects the operating range of the rotating impeller downstream. To improve the aerodynamic performance of centrifugal compressor it is necessary to suppress the separation and wake formation maintaining high level of diffusion within the impeller. It is essential to understand the ﬂow structure to achieve these objectives within the passages.
The complexity of the ﬂow in a centrifugal impeller impacts the performance of impeller and makes it difﬁcult to predict ﬂow ﬁeld correctly. Methods for accurate
author. E-mail address: firstname.lastname@example.org of Aerospace Engineering, Amir Kabir University of Technology, Tehran, Iran
Copyright © 2010 ICCES
ICCES, vol.14, no.1, pp.1-22
prediction of turbulent ﬂow in centrifugal impellers are important in order to get good estimate of the ﬂuctuating loads in impeller.
Signiﬁcant progress has been made in understanding impeller aerodynamic performance and also in predicting certain local ﬂow details. The most popular guide to impeller design is diffusion parameter of some sort. Dean  discussed the inﬂuence of internal diffusion on impeller efﬁciency. His results, showed a trend of increasing efﬁciency with an increased overall diffusion ratio. Overall diffusion ratio is deﬁned as the ratio of impeller inlet relative velocity, usually taken at the shroud, to impeller discharge relative velocity (w1 /w2 ). Kano et al.  presented results showing that in addition to the overall diffusion ratio, the rate of diffusion and maximum loading can signiﬁcantly impact impeller peak efﬁciency and range.
Moore et al.  used a three-dimensional viscous CFD method to examine the ﬂow in a medium pressure ratio impeller. The CFD results showed several aspects of loss production in the impeller. Loss production was high over most of the shroud particularly within the clearance ﬂow region. In most measurements of impeller efﬁciency, the inefﬁciency of the internal diffusion process is hidden by the large centrifugal pressure ratio. Detailed…