Graduate Seminar in Fluid Mechanics

September 13, 2019 @ 4:00 pm – 5:00 pm
Gilman 132

4:10 pm Presentation

An Input-Output Approach to Investigate the Effects of Actuator Geometry

 Presented by IGAL GLUZMAN (Adviser: Prof. Gayme)

In this work, an input-output approach is used to study actuated boundary layers arising from different types of input signals and actuator geometries. The manipulated flow fields are modeled using the Navier-Stokes equations linearized about a given base flow due to localized forcing. The actuated fields are then obtained by superposing the response of each localized source in a spatial pattern representing the actuation geometry, e.g., a serpentine geometry plasma actuator whose signal varies in intensity over the geometry. This framework allows the investigation of an array of actuation signals including a single pulse, a train of pulses, and a continuous input are modeled through analytical solutions of the LNS system. This talk will focus on the steady-state step response that is used to reproduce the stationary actuated flow-fields due to different plasma actuator configurations in transitional boundary layers. The model is found to reproduce the vortical and streamwise velocity structures obtained in experimental and simulation studies qualitatively well. Our results demonstrate the promise of such an analytical tool in determining beneficial actuator configurations prior to costly high-fidelity numerical simulations, and to reduce trial and error based parametric experimental studies.

4:35 pm Presentation

Heaving Stall Flutter of Blade in a Linear Cascade at Transonic Flow Speed”

 Presented by AYUSH SARASWAT (Adviser: Prof. Katz)

Aeroelastic flutter is a dynamic instability of a structure in a flow. When the structure undergoes flutter, the unsteady aerodynamic loads generated over it results in amplification of small oscillations. The flutter of turbomachine blades has been studied for decades but it has been difficult to fully understand it because of its sensitivity to a wide range of parameters and its occurrence over various conditions of turbomachine operation. To understand this phenomenon in the transonic regime, experiments were carried out on a linear cascade of compressor blades in a blowdown tunnel at M=1.3. The center blade was oscillated in heaving mode to simulate first bending mode oscillation of the near tip region of a rotor stage of an axial compressor. A barrel cam mechanism was employed to oscillate the blade up to 220 Hz. The parameters varied in the study were the reduced frequency of the blade and the pressure ratio of the cascade. It was observed that at low-pressure ratios the flutter map of the transonic cascade is qualitatively similar to subsonic stall flutter. However, at a high-pressure ratio, the observed trend was considerably different. Furthermore, shadowgraphs were used to visualize the flow, cascade periodicity, and passage shock structures.

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