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Dissertation/Thesis Abstract

Three-Dimensional Flowfield in a Swept Shock Wave/Boundary-Layer Interaction and Its Response to Pulsed Microjet Actuation
by Mears, Lee J., Ph.D., The Florida State University, 2020, 155; 28150179
Abstract (Summary)

Research efforts in shock wave/boundary-layer interactions (SBLI) are motivated by the pursuit of faster, lighter, and more maneuverable aircraft. Flow separation, strong pressure fluctuations, and high aerodynamic heating are all detrimental phenomena associated with these interactions. With a deeper understanding of the physics that drive the inherent unsteady pressure and shear forces, engineers can apply control techniques that target important flow regions and frequencies instead of overdesigning vehicles to survive these adverse effects. However, the mechanisms that drive the unsteady behavior in SBLI have been difficult to isolate and accurate predictions of unsteady pressure are not currently achievable for simulations with realistic Reynolds numbers. In order to further the understanding of 3-D SBLI physics, an experimental investigation of controlled perturbations introduced to a fin-generated swept shock wave/boundary-layer interaction is conducted.

The principal mean and unsteady flow features are studied with special emphasis on the difference between separation found in two-dimensional and three-dimensional interactions. Regions of high-amplitude pressure fluctuation on the surface beneath the interaction and coincident unsteady flow features above the surface are identified to support the development of physics-based models of interaction unsteadiness. Several techniques are employed to measure the flow response, including steady and unsteady surface pressure measurements using pressure-sensitive paint (PSP), shadowgraph to capture shock motion, particle image velocimetry (PIV) to quantify velocity fields in the flow, and high-bandwidth unsteady pressure sensors. Global measurement techniques, including steady and unsteady PSP, tomographic PIV, and multiple planes of high-speed stereo PIV permit uniquely illuminating analysis of the flow dynamics. Some of the experimental methods are novel for the facilities and types of flows, and validation and uncertainty quantification efforts are included.

Controlled flow perturbations, which have been historically difficult to implement in supersonic flows due to strong momentum of the flow and limited bandwidth of available actuators, are introduced within the interaction to gauge flow response to frequency and location of the disturbance. The perturbations are generated from Resonance-Enhanced Microjets (REM) which produce pulsed supersonic jets at frequencies on the order of several kilohertz. An evolution in the design of surface-mounted, modular REM actuators produces an improved implementation with greater repeatability and bandwidth. The frequency range studied here (between 2 and 4 kHz) has been selected based on separation and reattachment dynamics measured by unsteady pressure on the surface beneath the interaction.

Measurements combining the plate and heretofore-unstudied fin surface provide significantly more information about the response of this complex, highly three-dimensional interaction with details that are not easily obtained using traditional sensors. In general, the disturbances created by the actuators were found to excite convective mechanisms within the interactions and remained localized. Large-scale alterations in the flowfield due to microjet blowing are noted, including reduction of the size of separation and smaller shock traverse distances. The flow response to pulsed actuation reveals varying sensitivity of interaction key features, which offers promise for future efforts to design more effective flow control devices.

Indexing (document details)
Advisor: Alvi, Farrukh S.
Commitee: Jung, Sung-Moon, Kumar, Rajan, Oates, William, Yaghoobian, Neda
School: The Florida State University
Department: Mechanical Engineering
School Location: United States -- Florida
Source: DAI-A 82/8(E), Dissertation Abstracts International
Subjects: Fluid mechanics, Aerospace engineering, Mechanical engineering, Particle physics, Operations research, Design, Applied physics, Transportation
Keywords: Compressible flow, Particle image velocimetry, Pressure-sensitive paint, Supersonic wind tunnel, Unsteady flow control, Reynolds numbers, Shock wave boundary-layer interaction
Publication Number: 28150179
ISBN: 9798569968695
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