Flow through the turbine section of gas turbine engines is inherently unsteady due to a variety of factors, such as the relative motion of rotors and stators. In low pressure turbines, periodic wake passing has been shown to impact boundary layer separation, blade surface pressure distribution, and loss generation. The effect of periodic disturbances on the endwall flow is less understood. The present paper considers the response of an endwall vortical structure, the passage vortex, to various upstream disturbances. The passage vortex is a three-dimensional unsteady flow feature which generates aerodynamic losses as it interacts with the flow along the blade suction surface. High-speed velocimetry and numerical simulations have shown that the vortex intermittently loses coherence and varies in strength and position over time. The intermittent loss of coherence of the passage vortex is believed to be related to the leading-edge junction flow dynamics. An array of pneumatic devices was installed upstream of a linear cascade of low-pressure turbine blades to produce periodic disturbances that impact the blade leading edge region. The change in the unsteady characteristics of the vortex were analyzed under the influence of various upstream disturbances. This study expands upon previous experiments to include disturbances of two different magnitudes and over a larger frequency range. A small disturbance and a large disturbance were created and characterized by their maximum velocity deficit and nondimensionalized by the on-time of the solenoid valve. The characteristics of the disturbances, in terms of frequency, and velocity deficit are modified by changing the device's settings. A plane of P1V data was collected between the upstream device and the blade leading edge to characterize the periodic disturbances. A plane of high-speed SPIV data was collected inside the blade passage to examine how the disturbances impacted the vortex. The size and frequency of the disturbances had a nonlinear impact on the vortex size and strength. Fourier analysis revealed that the actuation frequency caused a harmonic response, and a change in the temporal behavior of the PV. The VITA method was implemented in this study to provide insight into the disturbance's impact on the PV. Each actuation frequency caused a different response from the vortex, but the vortex dynamics did not lock-on to the disturbance frequency.
展开▼
