Experimental Investigation of a Transonic Compressor with High Aspect Ratio Rotor Design

Abstract

This paper presents the results of an experimental investigation of a high aspect ratio rotor design. Future axial compressor designs for jet engines require increased efficiency in conjunction with reduced weight and size. Therefore, the investigation determines the influence of a decreased chord length on the rotor behavior. The experiments were carried out at the transonic compressor test rig at TU Darmstadt. The test rig represents a modern front stage highpressure compressor of a jet engine. The analysis is based on several measurements, using extensive steady and unsteady instrumentation, to obtain data for global compressor characteristics and performance as well as transient behavior, focusing on aerodynamic and aeromechanical phenomena. This paper compares the aerodynamic behavior of different transonic compressor stage setups, including an inlet guide vane and stator as well as three varying rotor designs. The baseline geometry design represents a modern low aspect ratio rotor (Rotor A). Based on that, the second rotor (Rotor B) is designed with an increased aspect ratio, resulting from an average chord length reduction of more than 20 % across the blade height. The blade height and rotors tip clearance as well as the solidity is kept constant, resulting in an increased blade count. By retaining constant testing conditions, all measurement data and observations can be merged, in order to describe the effects with respect to varying rotor aspect ratios. Therefore, the IGV and stator vanes as well as the entire instrumentation stays untouched during a rotor BLISK change. Five-hole-probe measurements at the rotor inlet show equal flow conditions for all setups. Comparing the compressor characteristics at design and part speed operation, the investigation shows a significant loss in stall margin and total pressure ratio. The aim of the desired future rotor design is to recover the losses due to a higher aspect ratio. Therefore, the investigation of this paper also includes a third rotor design (Rotor C). The mechanical and geometrical design parameters are the same as for Rotor B. The design is based on a numerical 3D optimization process. The experimental study is in line with the numerical predictions. Rotor C shows an equivalent behavior in total pressure rise and stall margin compared to the baseline (Rotor A) geometry. As a conclusion, this paper indicates the possibility to design a compressor rotor with a considerable reduced chord length and 3D optimized blading, without suffering significant losses in stall margin or total pressure rise.

Transonic Comrpessor Darmstadt – Open Test Case

“…Close to the wall the influence of the fully developed turbulent boundary layer is clearly identifiable and also shown in Figure 5 b for several operating conditions from near choke (NC) to near stall (NS). Except for the boundary layer, the flow variations in radial and circumferential direction are marginal within the inlet, which is also shown by Hormel et al (2019).…”

“…To predict the unsteady flow parameters, the probe is operated as a virtual three-hole probe (v3HP), measuring at three different probe angles (+45° / 0° / -45°) for each grid point. Thus, total pressure, Mach number and flow angles can be determined within the rotating frame of reference (see Hormel et al (2019) and Jüngst (2019)).…”

“…), aspect ratios (e.g. Hormel et al (2019)) or materials, novel stator designs, for example in tandem arrangement (e.g. Foret et al (2021)), as well as 1.5-stage setups with variable inlet guide vanes (e.g.…”

Transonic compressor Darmstadt - Open test case Introduction of the TUDa open test case

“…To predict the unsteady flow parameters, the probe is operated as a virtual three-hole probe (v3HP), measuring at three different probe angles (+45°/0°/−45°) for each grid point. Thus, total pressure, Mach number and flow angles can be determined within the rotating frame of reference (see Hormel et al, 2019;Jüngst, 2019). The rakes and traversable probes are aerodynamically calibrated at an in-house calibration wind channel, enabling Mach numbers within the range of expected operating conditions.…”

“…Franke et al, 2020a,b), aspect ratios (e.g. Hormel et al, 2019) or materials, novel stator designs, for example in tandem arrangement (e.g. Foret et al, 2021), as well as 1.5-stage setups with variable inlet guide vanes (e.g.…”