Nishul Arora

Shock-Boundary Layer Interaction due to a Sharp Unswept Fin in a Mach 2 Flow

An experimental study on the interaction of a swept shock wave, generated by a sharp fin, with a turbulent boundary layer is presented. An un-swept fin is placed in a Mach 2 flow where the interaction strength is varied by changing the angle of attack (α) from 10◦ to 15◦. This corresponds to flowfields that are weakly separated (α = 10◦) to fully separated (α = 15◦). Surface oil-flow is used to study the topography of the flowfield. Detailed velocity field measurements using two component Particle Image Velocimetry (PIV) are used to examine the structure of the interaction in a conical reference frame. Two slices of the velocity field at a distance of 1.5 in and 2.0 in from the fin apex (moving along the shock) are examined herein. Typical flow features, including the lambda-shock structure, the slip line and the separation bubble with reverse flow are clearly seen. The velocity field obtained confirm the quasi-conical behavior as well as the physical models developed earlier for this flowfield, which had mainly relied on detailed flow visualizations. To our knowledge, this is the first study that provides direct quantitative measurements of this flow in the appropriate quasi-conical frame of reference.

Volumetric Measurement of a Shock Wave-Turbulent Boundary Layer Interaction Using Plenoptic Particle Image Velocimetry

This paper explores the application of Plenoptic Particle Image Velocimetry (PIV) to study a Shock WaveTurbulent Boundary Layer Interaction (SBLI) induced by an unswept fin. The fin is placed in a Mach 2 flow at an angle of attack of 15◦. The oblique shock wave introduced by the fin interacts with the turbulent boundary layer along the bottom wall. A plenoptic camera is a unique diagnostic tool that captures 3D information using a single camera. This novel imaging system can be combined with particle image velocimetry to obtain 3D velocity data about a flow field. For comparison, the volume analyzed in this study relates to a previous study in the same facility using two planar PIV experiments separated by approximately 12 mm. This is the first application of a plenoptic camera for volumetric studies of SBLI, and it has proven the unique capabilities of the plenoptic camera to obtain 3D velocity information in areas of limited optical access and in supersonic flows. Comparison with previous planar PIV shows the same interaction structure present in both results.

Experiments on Resonance Enhanced Pulsed Microjet Actuators in Supersonic Cross flow

An array of high-bandwidth, high-momentum pulsed supersonic microjets, called Resonance Enhanced Microjets (REM), were implemented to study the effect of pulsed actuation in a M=1.5 supersonic cross flow over a flat plate. Cross correlated, phase locked flow imaging and unsteady pressure measurements were used to characterize the shock wave-boundary layer interactions resulting from the pulsed actuation. Pulsed microjet actuators in supersonic cross flow have generated oblique shocks whose strength and shock angle are observed to have an invariable correlation with the pulsing phase of the microjets. Unsteady pressure measured downstream also shows a strong correlation to the pulsing phase of the actuator and the resulting oblique shock properties. These experiments clearly point to the potential capabilities of the resonance enhanced microjet actuator to manipulate the unsteady properties of the boundary layer of a supersonic flow.