Interaction of Rotor and Casing Treatment Flow in an Axial Single-Stage Transonic Compressor With Circumferential Grooves

Abstract

The influence of circumferential grooves on the tip flow field of an axial single-stage transonic compressor rotor has been examined experimentally and numerically. The compressor stage provides a strongly increased stall margin with only small penalties in efficiency when the casing treatment is applied. Due to the complex interactions of the grooves with the rotor flow, unsteady measurement techniques have been chosen as an attempt to identify the aerodynamic effects responsible for the operating range extension. Therefore, the casing treatment has been instrumented with piezoresistive pressure sensors in the land between the grooves providing high-resolution static wall pressure measurements at different operating conditions. Data acquisition worked at a sampling rate of 125kHz, providing around 23 static pressure values per blade passage at 11 axial positions at the nominal speed of 20,000 rpm. A comparable dataset, but with 14 sensors, was obtained for the smooth casing. The results show the fluctuation of the tip leakage vortex and shock-vortex-interactions as well as the changed situation with casing treatment. Ensemble-averaged data shows tip leakage vortex trajectories. At near stall conditions with the smooth casing, the vortex hits the front part of the adjacent blade, which indicates the possibility of a spill forward of low momentum fluid into the next passage. Standard deviation values prove a high fluctuation of the pressure field over the tip gap. When the casing treatment is applied, the vortex trajectory maintains alignment along the blade’s suction side, thus preventing the onset of rotating stall. Results are presented as a back-to-back comparison of the smooth casing versus the treated casing at three operating conditions: peak efficiency at a mass flow rate of m˙pe = 16.2kg/s, near stall of the smooth casing at m˙nssc = 14.0kg/s and near stall of the treated casing at m˙ns = 12.6kg/s. Steady and unsteady numerical simulations of the rotor-only flow field have been calculated with and without grooves. These calculations aim at a broad analysis of the occurring flow phenomena at the rotor tip. Tip leakage flow behaviour and vortex trajectories are discussed in detail by summarizing the congruent findings of both numerical and experimental investigations.

Full Annulus Simulations of a Transonic Axial Compressor Stage with Distorted Inflow at Transonic and Subsonic Blade Tip Speed

“…Design features similar to the turbofans of jet engines are exhibited by rotor 1; therefore, the interactions with inlet distortions are assumed to be transferable to real engines. The compressor itself is well-known in open literature, and detailed information on the compressor has been published by, e.g., Schulze [10], Bergner [11], Biela et al [12], and Müller et al [13].…”

State-of-Art of Transonic Axial Compressors

“…9. Cross section of a transonic compressor stage with circumferential grooves (modified from Müller et al, 2008) Other possible groove-type casing treatment solutions are presented in Figs. 10 and 11.…”

An Investigation of the Mechanisms of Stall Margin Improvement in Casing Treatment with Bridge Structure

“…Casing treatment is a method that significantly improves the performance of a compressor/fan, and it has been developed into many forms since Koch C C [5][6][7][8][9] found that it can improve the compressor stability margin. The traditional casing treatment includes axial slots, circumferential grooves, and chordwise grooves [10][11][12][13][14][15][16]. Greitzer [10] concluded that the traditional casing treatment can extend the stall margin at the expense of efficiency loss.…”

“…Müller [13] used circumferential grooves on the rotor of a single-stage transonic compressor. The results showed that circumferential grooves improve the compressor stall margin and reduce the efficiency by less than 0.4%.…”