This study investigates the mean flow structure of two shock-wave boundary-layer interactions generated by moderately swept compression ramps in a Mach 2 flow. The ramps have a compression angle of either $19^{\circ }$ or $22.5^{\circ }$ and a sweep angle of $30^{\circ }$. The primary diagnostic methods used for this study are surface-streakline flow visualization and particle image velocimetry. The shock-wave boundary-layer interactions are shown to be quasi-conical, with the intermittent region, separation line and reattachment line all scaling in a self-similar manner outside of the inception region. This is one of the first studies to investigate the flow field of a swept ramp using particle image velocimetry, allowing more sensitive measurements of the velocity flow field than previously possible. It is observed that the streamwise velocity component outside of the separated flow reaches the quasi-conical state at the same time as the bulk surface flow features. However, the streamwise and cross-stream components within the separated flow take longer to recover to the quasi-conical state, which indicates that the inception region for these low-magnitude velocity components is actually larger than was previously assumed. Specific scaling laws reported previously in the literature are also investigated and the results of this study are shown to scale similarly to these related interactions. Certain limiting cases of the scaling laws are explored that have potential implications for the interpretation of cylindrical and quasi-conical scaling.
An impinging jet produces a highly unsteady flowfield which results in very high noise levels, harmful structural vibrations, and significant loss of lift and stability in applications such as the short takeoff and vertical landing aircraft. An understanding of the flowfield and implementation of an effective flow control technique are necessary to reduce these adverse effects. The presence of multiple impinging jets leads to the generation of a fountain flow, which further adds to the complexity of the flowfield dynamics. In the present study, flowfields of a single supersonic round jet (Mach 1.5) and dual impinging jets (consisting of a Mach 1.5 supersonic jet and an additional sonic jet) are explored. A microjet-based control method is applied to attenuate flow unsteadiness by modifying shear layer instability characteristics of the supersonic jet. Passive and active influence of the microjet hardware on acoustics are examined over a range of impingement distances (2.25D–10D) with a fine resolution (D/16) to obtain detailed resonance characteristics. Based on the resonance tone behavior as a function of impingement distances, detailed flowfield characteristics at certain impingement distances are investigated with the help of schlieren visualization, near-field acoustics, and unsteady surface pressure measurements. The effectiveness of the microjet flow control method in reducing noise is also evaluated in the flowfield of single and dual impinging jets. For single and dual impinging jets configuration, relative to their respective baseline cases, the microjet control on dual impinging jets shows better noise attenuation of overall sound pressure level within short impingement distances ([Formula: see text]).
In this study, a variation of the stacked stereoscopic PIV technique is proposed to perform fully volumetric (3-dimensions, 3-components) measurements of average flow fields within a single experiment through the usage of an automated traversing system that continuously scans the SPIV light sheet over a linear path. The simultaneous measurement of the traverse location and the laser Q-switch pulse enables the automated assignment of instantaneous PIV fields to known physical coordinates, enabling spatiotemporal averaging in postprocessing to obtain volumetric measurements of a flow field. This method provides a trade-off between spatial resolution of the volume measurements and statistical convergence of the spatiotemporal averages, enabling volumetric measurements under challenging experimental conditions where only stereoscopic PIV is viable.A comparison with the more traditional temporal averaging method and planar PIV are presented to demonstrate the capabilities and limitations of this technique in realistic, challenging experimental setups. It is found that the spatiotemporal averaging convergence behavior differs slightly from the traditional temporal averaging for the wake of a bluff body model, however relative errors lower than two standard deviations can still be attained. Thus, this technique presents a viable alternative for rapid 3D reconstruction of averaged flow fields that can provide invaluable insight of various flow topologies.
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