Modeling of Blade Tip Geometries in an Axial Compressor Stage

Abstract

The purpose of this paper is to investigate numerically the tip leakage flow for different blade tip geometries in an axial compressor stage under design and off-design conditions. Using flat tips, suction and pressure side squealers in combination with knife tips, a comparison of the rotor performance in terms of pressure and efficiency gain is reported. Detailed flow characteristics within the tip clearance gap, interaction of the leakage flow with the main flow and resultant turning effects at the exit of the row have been investigated. The CFD method is based on a commercially available compressible Navier-Stokes solver (STAR-CD), using a turbulent compressible high Reynolds number k-ε model. Accurate numerical comparison of different blade tip geometries is achieved by using the same grid for the various shapes. The blocking strategy with O-grid structure is presented. The numerical results show clearly the beneficial effect of cutting away material from the pressure side. The higher surface curvature of the suction side squealer affects the pressure blade loading and increases the lift in the same way. This effect is increased by increasing the squealer height and results in a lower efficiency gain near the surge line. The best modification of the blade tip shows a maximum reduction of the tip discharge coefficient of 20 %. This leads to an improved total pressure ratio of 0.29% and an improved total polytropic efficiency of 0.40% under design condition. The influences of favourable squealer geometries on stage characteristics are described along an operating line. With a simulation of IGV-setting from Δα = −15° to Δα = +20° different operating points have been investigated in a swirl performance map. The beneficial effect of the suction side squealer found for the rotor row could assign to the stator row and results in an improved static pressure gain. Furthermore, design indications are presented which help to keep the efficiency gain under surge condition as high as possible.

Influence of blade tip cutting on axial compressor aerodynamic performance

“…Stockhaus [3] had the same conclusion. The authors of this article believed that the difference in leading edge geometry essentially affected the inflow attacking angle, which directly controlled the flow condition after it entered into the blade passage.…”

“…Comparing to Stockhaus' work [3], the total pressure ratio was improved by ∼0.29 per cent and polytropic efficiency by 0.4 per cent the maximum. These were about the same level as the results in this article.…”

“…Figure 3 shows the geometry of Cut1. The idea for Cut1 originated from Stockhaus' conclusion [3], which pointed out that the increased curvature of the midchord contributed the most to the improvement of rotor pressure rise. For Cut1, the leading and trailing edges retained the same shape as the original blade to focus the effect on the increased mid-section curvature.…”

“…Figure 3 shows the geometry of Cut1. The idea for Cut1 originated from Stockhaus' conclusion [3], which pointed out that the increased curvature of the midchord contributed the most to the improvement of Fig. 3 Geometry of Cut1 Fig.…”

“…In the most recent years, the development of computational fluid dynamics (CFD) technology enables researchers to learn more about blade tip cutting by * Corresponding author: School [3] numerically investigated four kinds of tip cutting geometries on a highly subsonic compressor, and concluded that the midchord suction side squealer could increase the stage total pressure rise and rotor efficiency. Shao [4] studied the blade tip cutting effect on Rotor 37.…”