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research-article

TRANSIENT PERFORMANCE OF SEPARATED FLOWS: CHARACTERIZATION AND ACTIVE FLOW CONTROL

[+] Author and Article Information
Jorge Saavedra

Purdue University, West Lafayette, IN, USA; von Karman Institute for Fluid Mechanics, Rhode-Saint-Genèse, Belgium
jorsaaga@gmail.com

Guillermo Paniagua

Purdue University, West Lafayette, IN, USA; von Karman Institute for Fluid Mechanics, Rhode-Saint-Genèse, Belgium
gpaniagua@me.com

1Corresponding author.

ASME doi:10.1115/1.4040685 History: Received June 22, 2018; Revised June 22, 2018

Abstract

The aerothermal performance of the low pressure turbine in UAVs' is significantly abated at high altitude, due to boundary layer separation. Different flow control strategies have been proposed to prevent boundary layer separation, such as dielectric barrier discharges, synthetic jets. However, the optimization of the control approach requires a better characterization of the separated regions at transient conditions. The present investigation analyzes the behavior of separated flows, reporting the inception and separation length, allowing the development of efficient flow control methods under non-temporally uniform inlet conditions. The development of separated flows were investigated with numerical simulations including Unsteady Reynolds Average Navier Stokes and Large Eddy Simulations. The present research was performed on a wall mounted hump, which imposes a pressure gradient representative of the suction side of low pressure turbines. Through sudden flow accelerations we looked into the dynamic response of the shear layer detachment as it is modulated by the mean flow evolution. Similarly, we studied the behavior of the recirculation bubble under periodic disturbances imposed at various frequencies ranging from 10 to 500 Hz, at which the Reynolds number oscillates between 40000 and 180000. As a first step into the flow control we added a slot to allow flow injection and ingestion upstream of the separation inception. Exploring the behavior of the separated region at different conditions we defined the envelope for its periodic actuation. We found that matching the actuator frequency with the frequency response of the separated region the performance of the actuation is boosted.

Copyright (c) 2018 by ASME
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