Abstract
The objective of the present investigation is to examine the possibility of performance improvement, improvement of the exit flow uniformity and desensitization of the tip clearance effects on the performance of a low speed centrifugal impeller. Computational investigations using a commercial CFD software are undertaken. Six configurations of blade tips are investigated. They are square tip (Basic), tip chamfered on pressure surface (P1 and P2), tip chamfered on suction surface (P1 and P2) and tip chamfered on pressure and suction surfaces (PS1). Computations are carried out with optimized multiblock grids for these six configurations at five flow coefficients, namely 0.28 and 0.34 (below design flow coefficient), 0.42 (design flow coefficient) and 0.48 and 0.52 (above design flow coefficient) and at three values of tip clearance, viz., 1% (small value), 2% (nominal value) and 5% (large value) of the blade exit height. From the investigations, it is found that the impeller with the chamfer on suction surface shows small improvement in performance. In addition this configuration has minimum tip clearance sensitivity. A decrease in the chamfer on suction surface further may improve the impeller performance. A maximum percentage of 0.18% improvement in the total pressure coefficient is obtained at 5% tip clearance and a flow coefficient of 0.52 for configuration S2. However chamfer on the pressure surface deteriorates the impeller performance.
Highlights
The centrifugal compressor is widely used in process industries, turbochargers, small gas turbine engines, etc
The flow field in the centrifugal impeller is influenced by the complex curvature of the impeller blades, the rotational forces, and clearance between the rotating impeller and stationary casing
On pressure surface the blade tip is cut in three directions, 5 mm along blade height, 20 mm along blade pressure surface away from trailing edge and 1/3rd (1 mm) of blade thickness along blade thickness direction
Summary
The centrifugal compressor is widely used in process industries, turbochargers, small gas turbine engines, etc. Computational investigation of flow field in a centrifugal impeller with chamfered blade tips is carried out in the present paper, to examine the possibility of performance improvement, improvement of the exit flow uniformity and desensitization of the tip clearance effects. Computational study is conducted to analyse the effects of tip geometry in the centrifugal impeller by chamfering blade tip Both winglet or partial shroud and squealer tip are made of extremely thin material. The objective is to use impeller tip chamfering as a mean to improve the performance of the impeller in terms of increased pressure rise, increased efficiency, and increased stability and operating range It is examined if chamfering will improve the uniformity of exit flow and desensitize the tip clearance effects. The computations are carried out at six impeller tip configurations, namely basic square tip configuration, with small and large chamfers on the suction and pressure surfaces and chamfer on both suction and pressure surfaces
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