On the Applicability of a Spoked-Wheel Wake Generator for Clocking Investigations

A comprehensive investigation was carried out using two different experimental setups: A 1.5-stage axial turbine and a simplified model, a “spoked-wheel” setup with a rotating wake generator consisting of cylindrical bars. The second stator of the turbine was designed at MTU Aero Engines as a high-lift profile with a Reynolds number typical for low-pressure turbines in jet engines. At design conditions, the flow on the stator 2 suction side features a pronounced separation bubble. To study the behavior of the stator 2 boundary layer and the interaction mechanisms between stator and rotor wakes, different measurement techniques were used: X-wire probes, five-hole probes, static pressure tappings, and surface mounted hot-film gauges. It was found that a rotating wake generator of the spoked-wheel type is not capable of resolving the relevant clocking mechanisms that occur in a real engine. However, such a simplified setup is useful to separate some of the physical mechanisms, and in case that the interaction of the stator 1 wakes with the stator 2 boundary layer is negligible, a spoked-wheel setup is well suited to simulate the influence of periodically incoming wakes on the transition behavior of stator 2.