Unsteady Aerodynamical Blade Row Interaction in a New Multistage Research Turbine: Part 1 — Experimental Investigation

Abstract

Exploitation of stator–stator interaction phenomena can increase overall efficiency in axial turbomachines. The first part of this paper sets out to present results of steady and unsteady flow experiments obtained in a new three stage cold flow low pressure turbine. Observation and understanding of boundary layer development and transition phenomena on the vanes dependent on relative stator position will be the focal point. In addition to this, stator position influence on profile loss, turbine efficiency and the development of secondary flow are examined. The experiments were carried out in the closed circuit test bed of the Institute of Aeronautical Propulsion at Stuttgart University. Annulus geometry and blading design of the research turbine were taken from the low pressure turbine of a modern commercial jet engine. The three stage test rig had identical blade counts for all stators or rotors respectively, whilst the circumferential position of each stator row could be individually adjusted. The second and third stators were optimised with respect to the radial alignment of the vanes. Surface mounted hot film gauges on the vanes and hot film probes were employed to assess the unsteady interaction phenomena. For steady measurements, pneumatic five hole probes and multiple kielhead pressure and temperature probes were used. For both the second and third stator, circumferential position was varied in eight steps over one pitch. Whereas the design point forms the basis of this detailed investigation, some attention was also paid to variations in Reynolds number and wheel speed. The results, such as quasi wall shear stress, stochastic and periodic fluctuations, total pressure etc., are presented in the form of chordwise ensemble-averaged distributions and contour plots and should be compared with the corresponding numerical studies presented in the second part of this paper.