Bulletin of the American Physical Society
70th Annual Meeting of the APS Division of Fluid Dynamics
Volume 62, Number 14
Sunday–Tuesday, November 19–21, 2017; Denver, Colorado
Session D30: Compressible Flow: External Shock-Boundary Layer InteractionCompressible
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Chair: Anne-Marie Schreyer, RWTH Aachen University, Institute of Aerodynamics Room: 110 |
Sunday, November 19, 2017 2:15PM - 2:28PM |
D30.00001: PIV measurements in two hypersonic shock wave / turbulent boundary layer interactions Anne-Marie Schreyer, Owen Williams, Alexander J. Smits Particle Image Velocimetry measurements were performed to study two compression corner interactions in hypersonic flow. The experiments, carried out at Mach 7.2 and at a Reynolds number based on momentum thickness of 3500, included mean flow surveys as well as turbulence measurements in the near-field of the interaction. For the $8^{\circ}$ compression corner, the flow remained attached, and for the $33^{\circ}$ compression corner a large separation bubble formed. For the attached case, the influence of the shock wave on the streamwise turbulence intensities is weak, but the wall-normal component and the Reynolds shear stress show considerable amplification. In the fully separated case, both the streamwise and wall normal velocity fluctuations, as well as the Reynolds shear stresses, show strong amplification across the interaction. In contrast with the behavior in the attached case, equilibrium flow is approached much more rapidly in the separated case. Turbulence measurements in such complex hypersonic flows are far from trivial, with particle frequency response limitations often significantly reducing the measured wall-normal turbulence. We will therefore discuss these influences on overall data quality as well as the interpretation of flow physics based on these results. [Preview Abstract] |
Sunday, November 19, 2017 2:28PM - 2:41PM |
D30.00002: Non-equilibrium Effects of a Hypervelocity Flow over a Double Wedge Geometry Nelson Yanes, Joanna Austin Hypersonic flow over a double wedge geometry is a canonical example of a shock-boundary layer interaction. At higher stagnation enthalpies (\textgreater 5MJ/kg) with an air free-stream, real gas effects become significant in influencing the shock interaction. To uncover the role of thermochemistry effects in a shock-boundary layer system, spectroscopic measurements of nitric oxide (NO) vibrational temperature are made. The Hypervelocity Expansion Tube (HET) is used to generate high Mach number, high enthalpy flow over a 30-55 degree double wedge. The UV portion of the NO gamma band is captured in the range of 220-255 nm. Vibrational temperature measurements are taken at various flow locations and free-stream conditions, where type IV and V shock configurations are investigated. [Preview Abstract] |
Sunday, November 19, 2017 2:41PM - 2:54PM |
D30.00003: On the Unsteadiness of a Transitional Shock Wave-Boundary Layer Interaction Using Fast-Response Pressure-Sensitive Paint E. Lara Lash, John Schmisseur Pressure-sensitive paint has been used to evaluate the unsteady dynamics of transitional and turbulent shock wave-boundary layer interactions generated by a vertical cylinder on a flat plate in a Mach 2 freestream. The resulting shock structure consists of an inviscid bow shock that bifurcates into a separation shock and trailing shock. The primary features of interest are the separation shock and an upstream influence shock that is intermittently present in transitional boundary layer interactions, but not observed in turbulent interactions. The power spectral densities, frequency peaks, and normalized wall pressures are analyzed as the incoming boundary layer state changes from transitional to fully turbulent, comparing both centerline and outboard regions of the interaction. The present study compares the scales and frequencies of the dynamics of the separation shock structure in different boundary layer regimes. Synchronized high-speed Schlieren imaging provides quantitative statistical analyses as well as qualitative comparisons to the fast-response pressure sensitive paint measurements. [Preview Abstract] |
Sunday, November 19, 2017 2:54PM - 3:07PM |
D30.00004: Shock waves and obstacles: a tale of multiple reflections Alexander Ivanov, Christina Scafidi, Nicolas Fassardi, Tugra Gokcay, Sara Dominguez, Ingrid Rivera, Veronica Eliasson The interaction of a planar shock wave with multiple square obstacles (containing one, two or three semi-circular grooves) arranged in the shape of a logarithmic spiral is studied to find the attenuation characteristics of both the transmitted and reflected shock waves. The experiments are performed using a conventional horizontal shock tube with an inner square-shaped cross section. Three shock wave Mach numbers, M = 1.2, 1.25, and 1.4 are investigated using high-speed schlieren photography and pressure measurements. The attenuation characteristics for all cases are compared using a non-dimensional attenuation factor for both the transmitted and reflected shock waves. Results will be discussed for the varying incident shock Mach numbers and obstacles with different number of grooves in. [Preview Abstract] |
Sunday, November 19, 2017 3:07PM - 3:20PM |
D30.00005: 50 kHz PIV Investigation of Swept Compression Ramp Shock / Boundary Layer Interactions Leon Vanstone, Mustafa Nail Musta, Serdar Seckin, Noel Clemens The shock/boundary-layer interaction (SBLI) of a swept (30$^{\circ}$) compression ramp (22.5$^{\circ}$) in a Mach 2 flow is examined using 5 Hz and 50 kHz PIV in both streamwise-tranverse and streamwise-spanwise planes. The mean u-velocity component exhibits conical symmetry in accord with previous studies, but the weaker velocity components (v, w) do not. We argue that moderately-swept interactions possess an extended inception region where the separated flow takes additional distance to reach its asymptotic state. The high-speed PIV is band-pass filtered to investigate driving mechanisms of unsteadiness of the separated flow. We looked at three distinct frequency bands: low (0-1 kHz), mid (1-10 kHz), and high (10-50 kHz). Unlike unswept interactions, the majority (80%) of the amplitude exists in the mid- and high-frequency bands. The mid-frequency unsteadiness appears correlated with inflowing velocity fluctuations that are most likely driven by boundary-layer superstructures. The high-frequency unsteadiness seems related to shear layer activity and a new high-frequency mechanism related to structures in the separated flow. The unsteadiness of this swept-ramp SBLI is then compared to a similar unswept compression ramp to show differences between 2D and 3D interactions. [Preview Abstract] |
Sunday, November 19, 2017 3:20PM - 3:33PM |
D30.00006: Quantification of Streamline Vectors and Application to Surface Characteristics of Swept Shock Wave/Boundary Layer Interactions (SBLI) Lee Mears, Nishul Arora, Andrew Baldwin, Farrukh Alvi, Jonathan Naughton Surface streamlines obtained using surface oil visualization typically provide a qualitative perspective on the salient characteristics of complex flows, including lines of separation and reattachment. This is especially important for complex, 3D flow fields such as the separated region beneath a fin-generated swept shock wave/boundary layer interaction (SBLI). This study focuses on quantitatively processing limiting surface streamlines using a PIV-based cross-correlation technique to determine displacement vectors between successive images. Initial skin friction measurements in SBLI that require quantitative surface streamline information will be discussed. Furthermore, controlled unsteady disturbances are introduced using high-momentum Resonance Enhanced Microjets (REM) at two wall locations - upstream of the interaction and underneath the separated region. The surface streamlines and skin friction measurements provide a framework to examine the global flow response and how disturbances propagate within the interactions, which is useful for improving the current understanding of swept SBLI dynamics. [Preview Abstract] |
Sunday, November 19, 2017 3:33PM - 3:46PM |
D30.00007: ABSTRACT WITHDRAWN |
Sunday, November 19, 2017 3:46PM - 3:59PM |
D30.00008: ABSTRACT WITHDRAWN |
Sunday, November 19, 2017 3:59PM - 4:12PM |
D30.00009: Time-Resolved Planar Velocimetry of the Supersonic Wake of a Wall-Mounted Hemisphere Steven Beresh, John Henfling, Russell Spillers Time-resolved particle image velocimetry (PIV) was conducted at 40 kHz using a pulse-burst laser in the supersonic wake of a wall-mounted hemisphere. Velocity fields suggest a recirculation region with two lobes in which flow moves away from the wall near centerline and recirculates back towards the hemisphere off centerline. Spatio-temporal cross-correlations and conditional ensemble averages relate the characteristic behavior of the unsteady shock motion to the flapping of the shear layer. At Mach 1.5, oblique shocks form associated with vortical structures in the shear layer and convect downstream in tandem; a weak periodicity is observed. Shock motion at Mach 2.0 appears somewhat different, wherein multiple weak disturbances propagate from shear layer turbulent structures to form an oblique shock that ripples as these vortices pass by. Bifurcated shock feet coalesce and break apart without evident periodicity. Power spectra show a preferred frequency of shear layer flapping and shock motion for Mach 1.5, but at Mach 2.0 a weak preferred frequency is found only for the oblique shock motion and not the shear layer unsteadiness. [Preview Abstract] |
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