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.

Stator-clocking effects on the unsteady interaction of secondary flows in a 1.5-stage unshrouded turbine

“…The effect of clocking on turbine efficiency has been demonstrated in a number of studies (experimental: Huber et al [1], Gombert and Höhn [2], Reinmöller et al [3], Tiedemann and Kost [4]; numerical: Bohn et al [5]). In these studies the circumferential position of the wake of the upstream stator relative to the leading edge of the subsequent stator was mainly held responsible for the effect on efficiency.…”

Clocking effects on aerodynamics of a gas turbine low pressure axial turbine, part 2: Unsteady simulation

“…Using potential flow formulation, Swirydczuk concluded that under an optimum clocking position, a special form of upstream wake vortices is shed within the blades passage which increases dynamic pressure and consequently outlet total pressure at blade throat. 22 Other wake tracking analyses can be referred to some researchers like Hodson, 23 Jouini et al, 24 Gombert et al, 25 and Arndt. 26 These researchers reported that the blade-wake interactions can be controlled by clocking mechanism to influence the aerodynamic performance of axial turbines, including turbine efficiency, profile loss, boundary layer transition, and development of the secondary flows.…”

Unsteady Interaction Between a Transonic Turbine Stage and Downstream Components

“…Significant experimental and numerical research has been performed over the last several years on highlighting and understanding the unsteady aerodynamics of multi-stage turbomachinery (e.g., Reinmoller et al, 2001;Arnone et al, 2001;Gombert and Hohn, 2001;Dorney et al, 2001;Clark et al, 2000;Busby et al, 1998;Rao et al, 1994;Chen et al, 1994;Sharma et al, 1992;Takahashi and Ni, 1991;Giles, 1990;Jorgenson and Chima, 1990;Rai, 1987;Dring et al, 1992). Much of this work has focused on quantifying the unsteady flow field resulting from the interaction between rotors and stators in terms of aerodynamic performance and airfoil surface unsteady pressure.…”