Session: 05-13 Instrumentation III: Intrusive Measurement

Paper Number: 122780

122780 - Flow Disturbance by Intrusive Instrumentation: Part 2 – Protrusions on the Suction Side of HP Compressor Vanes 

In our study, we experimentally and numerically quantify the aerodynamic impact of spanwise pressure tube alike protrusions on either the suction side or pressure side of a high-pressure compressor stator vane. In this paper, which is the second part of our study, we focus on the effects of the protrusions located on the suction side. In part 1 of this study, which is submitted separately to ASME2024, the effects of the pressure side protrusions are explored.

Our experiments are carried out in a linear cascade wind tunnel at a Mach number of approx. 0.5 and a Reynolds number of 790,000. By varying the dimensions of the protrusions, we confirm the expectation that the generated total pressure losses strongly increase when increasing the height of the tubes. Additionally, we somewhat unexpectedly find that the losses are reduced significantly when increasing the width of the protrusions.

For the application in our linear cascade, the protrusions are modelled as a generic bump geometry. The protrusion’s shape and dimensions are derived from intrusive instrumentation typically found on vanes of compressor rigs such as pressure tubes of static profile pressure taps or Kielhead probes located at the leading edge. Cables of multiple strain gauges glued to the vane surface can have a similar shape.  In total, we test six suction-sided protrusion configurations. The width of the protrusion varies between 8% and 24% of the chord length, while the height varies between 33% and 66% of the maximum vane thickness. The beginning of all protrusions, which is tangential to the vane surface, is always located at 30% of the streamwise surface length. The protrusions extend over the entire span of the vane. In our linear cascade wind tunnel, one modified vane is installed with four nominal vanes on both sides. This setup is similar to the application in an axial rig, where only a few vanes of a stator row are modified.

For the 66% height, two protrusions of 8% and 24% width are tested. The resulting integral total pressure loss coefficient is increased by a factor of 5.7 and 4.1 compared to the loss of a nominal vane. At a height of 33%, widths of 8%, 16%, 20% and 24% are investigated. The protrusion of 8% width results in an increase in loss by a factor of 2.6. All other protrusions of 33% height are associated with a constant total pressure loss increase of approximately factor 2.1 Through oil flow visualisations as well as numerical simulations, we are able to show that the large loss increase for the 66% height are related to a complete flow separation downstream of the beginning of the protrusion. There is no reattachment of the flow on top of the protrusion for either width, resulting in a large, open recirculation zone. At a height of 33%, the results differ: complete flow separation downstream of the beginning of the protrusion only occurred at a width of 8%. For all other protrusion widths, the flow reattaches on top of the protrusion.

In summary, we provide qualitative and – for the given parameters also - quantitative data on the effect of protrusions located on the suction side of a compressor vane. Depending on the dimensions of the protrusions, the increase in total pressure loss varies significantly. Test engineers can use these results as a guide to design their intrusive instrumentation on compressor vanes to minimize additional total pressure loss. In future work, we will present methods to correct the influence of these protrusions on the overall compressor efficiency.

Presenting Author: Lukas Schäflein Institute of Jet Propulsion and Turbomachinery, RWTH Aachen University

Presenting Author Biography: Aerospace Engineering M.Sc. from Technical University of Munich
PhD student at Institute of Jet Propulsion and Turbomachinery, RWTH Aachen University
Research interest: influence of intrusive instrumentation on the flow in a compressor cascade

Authors:

Lukas Schäflein Institute of Jet Propulsion and Turbomachinery, RWTH Aachen University
Daniel Jung Institute of Jet Propulsion and Turbomachinery, RWTH Aachen University
Peter Jeschke Institute of Jet Propulsion and Turbomachinery, RWTH Aachen University
Roland Wunderer MTU Aero Engines AG