Comparative Study of Tip Injection in a Transonic and Subsonic Compressor

Abstract

Discrete tip injection is an effective method to enhance stability of compressors. This study compares the effects of injection parameters on compressor performance and underlying mechanisms in two different compressors. The transonic compressor is studied using unsteady simulations and the subsonic compressor is mainly investigated with experiment. Results show that tip injection improves stable operating range by 35.6% and 77.9% for the transonic compressor and subsonic compressor, respectively, without decreasing compressor efficiency. The effects of circumferential coverage percentage and injector throat height on compressor stability are similar in the two compressors when the injection velocity is double the velocity of main flow. The optimal injector throat height which is normalized by the tip clearance size is the same for the two compressors, and the best circumferential coverage percentage for the subsonic compressor is lower than that in the transonic compressor. For the two compressors, the adaption of the main flow to the discrete tip injection is unsteady, and the hysteresis effect that the recovery of tip blockage lags behind the recovery of tip leakage vortex accounts for the improved stability using partial coverage of injection. The injection efficiency, which is defined to quantify the improved quality of the flow field in the injection domain, is proven to determine the stall limits by studying the effects of several injection parameters. The guidelines built in the subsonic compressor can be used in the transonic compressor to design tip injection, but the optimal values of some injection parameters should be reconfirmed.

An overall blockage attenuation-based aerodynamic performance and stability design optimization method for transonic axial flow compressors

“…The predicted overall pressure ratio matches the measured data fairly well, whereas the calculated adiabatic efficiency is underestimated slightly. This efficiency underestimation is consistent with the RANS-based results in published studies, such as the research (Bruna and Turner, 2013) conducted by NASA using ANSYS CFX and other recent studies (Xu et al , 2020; Wang et al , 2022; Lang et al , 2021). In addition, the near-stall point predicted based on unsteady simulation is very close to the experiment stall mass.…”

“…The performance curve is calculated using a single passage (0.84 × 10 6 nodes) steady simulation with a CFL number of 3, and the unsteady simulation based on six-blade passages (5.04 × 10 6 nodes) is used to capture the near-stall point more accurately. In the unsteady simulation, the physical time steps and the maximum number of inner iterations of the dual time stepping approach are set as 60 and 20 (Wang et al , 2022), respectively. The convergence of the steady simulation is judged by the global root mean square residuals (less than 10 −5 ) and the relative deviation of the inlet and outlet mass flow rates (less than 0.2%).…”

“…Both stall mechanisms are closely related to the increase in the magnitude of the blockage in the tip flow passage during the compressor throttling process. In addition, numerous studies on the effect of passive (Sakuma et al , 2013; Chen et al , 2013; Moller et al , 2018) and active (Beheshti et al , 2006; Khaleghi et al , 2016; Wang et al , 2022) stability enhancement techniques on the flow mechanism of transonic AFCs have shown that the reduction of the blockage in the rotor tip region is the main reason for the stall margin improvement of AFCs.…”

Extending Highly Loaded Axial Fan Operability Range Through Novel Blade Design

“…Significant efforts to improve the stability range of fans and compressors have been made, mostly through the application of casing treatments [18,19] or tip injection [20,21]. These methods have been proved successful in extending the range of safe operation, but their introduction is commonly associated with performance deficits.…”