Bulletin of the American Physical Society
69th Annual Meeting of the APS Division of Fluid Dynamics
Volume 61, Number 20
Sunday–Tuesday, November 20–22, 2016; Portland, Oregon
Session D5: Compressible Flow: Shock-Boundary Layer Interaction |
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Chair: Venkateswaran Narayanaswamy, North Carolina State University Room: B113 |
Sunday, November 20, 2016 2:57PM - 3:10PM |
D5.00001: Experimental Investigation of SBLI to Unravel Inlet Unstart Physics Morgan Funderburk, Venkateswaran Narayanaswamy The phenomenon of shock boundary layer interaction (SBLI) driven inlet unstart persists as one of the most significant problems facing supersonic ramjet/scramjet engines. In order to determine how the characteristics of the SBLI units specific to rectangular inlets evolve during an unstart event, an experimental investigation is made using surface streakline methods and pitot/wall pressure measurements in the vicinity of the floor and corner SBLI induced by a compression ramp in a rectangular channel. Mean and unsteady measurements were taken at a variety of shock strengths to simulate the evolution of the combustion-induced back pressure ratio during unstart. The freestream Mach number was also varied. Statistical correlation methods were used to determine the degree of interaction between the floor and corner SBLI with different flowfield locations for the various test conditions. Finally, comparison to a two-dimensional compression ramp SBLI was made to determine any modification caused by the introduction of the corner SBLI. Results indicate that the floor and corner SBLI transition from distinct units to members of a global separated flow with increasing back pressure, and that considerable modification of the floor SBLI by the corner flow occurs. [Preview Abstract] |
Sunday, November 20, 2016 3:10PM - 3:23PM |
D5.00002: Sensitivity of shock boundary-layer interactions to weak geometric perturbations Ji Hoon Kim, John K. Eaton Shock-boundary layer interactions can be sensitive to small changes in the inlet flow and boundary conditions. Robust computational models must capture this sensitivity, and validation of such models requires a suitable experimental database with well-defined inlet and boundary conditions. To that end, the purpose of this experiment is to systematically document the effects of small geometric perturbations on a SBLI flow to investigate the flow physics and establish an experimental dataset tailored for CFD validation. The facility used is a Mach 2.1, continuous operation wind tunnel. The SBLI is generated using a compression wedge; the region of interest is the resulting reflected shock SBLI. The geometric perturbations, which are small spanwise rectangular prisms, are introduced ahead of the compression ramp on the opposite wall. PIV is used to study the SBLI for 40 different perturbation geometries. Results show that the dominant effect of the perturbations is a global shift of the SBLI itself. In addition, the bumps introduce weaker shocks of varying strength and angles, depending on the bump height and location. Various scalar validation metrics, including a measure of shock unsteadiness, and their uncertainties are also computed to better facilitate CFD validation. [Preview Abstract] |
Sunday, November 20, 2016 3:23PM - 3:36PM |
D5.00003: 3D Plenoptic PIV Measurements of a Shock Wave Boundary Layer Interaction Brian Thurow, Johnathan Bolton, Nishul Arora, Farrukh Alvi Plenoptic particle image velocimetry (PIV) is a relatively new technique that uses the computational refocusing capability of a single plenoptic camera and volume illumination with a double-pulsed light source to measure the instantaneous 3D/3C velocity field of a flow field seeded with particles. In this work, plenoptic PIV is used to perform volumetric velocity field measurements of a shock-wave turbulent boundary layer interaction (SBLI). Experiments were performed in a Mach 2.0 flow with the SBLI produced by an unswept fin at 15\textdegree angle of attack. The measurement volume was 38 x 25 x 32 mm$^{\mathrm{3}}$ and illuminated with a 400 mJ/pulse Nd:YAG laser with 1.7 microsecond inter-pulse time. Conventional planar PIV measurements along two planes within the volume are used for comparison. 3D visualizations of the fin generated shock and subsequent SBLI are presented. The growth of the shock foot and separation region with increasing distance from the fin tip is observed and agrees with observations made using planar PIV. Instantaneous images depict 3D fluctuations in the position of the shock foot from one image to the next. [Preview Abstract] |
Sunday, November 20, 2016 3:36PM - 3:49PM |
D5.00004: The Effect of Configuration on Shock/Boundary Layer Interaction Unsteadiness James Threadgill, Paul Bruce Low-frequency flow unsteadiness associated with shock/boundary layer interactions (SBLIs) remain poorly understood. Upstream and downstream mechanisms have been observed to drive the dynamics, with the latter more prevalent in higher strength interactions. Studies have typically focused on single SBLI configurations within a given environment, limiting identification of unique characteristic behaviors. An investigation has been conducted to assess the unsteady behavior of various 2D SBLIs, each with a range of interaction strengths, all tested within a single facility. Experiments were conducted in Mach 2 flow with Re$_\theta=8000$, featuring 14$^\circ$ and 20$^\circ$ compression ramps, and impinging shock reflections from $7^\circ$, $8^\circ$, $9^\circ$, and $10^\circ$ shock generators. Resultant SBLIs were analyzed using high-speed planar PIV and a streamwise array of fast-response wall-pressure transducers. High-frequency energy content of the shock motion is observed to be independent of the configuration. The dominance of the downstream mechanism in low-frequency unsteadiness is related to the SBLI configuration as well as the interaction strength. In addition, correlations between shock position and angle, and the separated near-wall flow structure are directly established. [Preview Abstract] |
Sunday, November 20, 2016 3:49PM - 4:02PM |
D5.00005: 50 kHz PIV of a Swept-Ramp Shock-Wave Boundary-Layer Interaction at Mach 2. Leon Vanstone, Mustafa Nail Musta, Serdar Seckin, Mohammad Saleem, Noel Clemens The interaction from a 30$^{\circ}$ sweep, 22.5$^{\circ}$ compression ramp in a Mach 2 flow is examined using wide-field 5Hz and 50 kHz PIV. The high-speed PIV is fast enough to resolve the large-scale unsteady motions of the SWBLI and can be band-pass filtered to investigate the driving mechanisms of unsteadiness and the widefield PIV allows comparisons with mean flow-fields. Preliminary investigation looked at three distinct frequency bands: 10-50 kHz (0.025-0.25 $U_{\infty}/\delta_{99}$), 1-10 kHz (0.025-0.25 $U_{\infty}/\delta_{99}$), and 0-1 kHz (0-0.025 $U_{\infty}/\delta_{99}$). The unsteadiness associated with 10-50 kHz shows no correlation with the upstream boundary layer and accounts for 40% of the amplitude. The unsteadiness associated with 1-10 kHz is correlated with the upstream boundary-layer and also accounts for 40% of unsteadiness. This frequency is similar to those of boundary-layer superstructures. The unsteadiness associated with 0-1 kHz shows the strongest correlation with the upstream boundary-layer but accounts for only 20% of the amplitude. Clearly a range of unsteadiness mechanisms are present, with significant amplitude associated with higher frequencies. Future work will focus on expanding these findings with surface pressure and additional PIV. [Preview Abstract] |
Sunday, November 20, 2016 4:02PM - 4:15PM |
D5.00006: Influence of Mach Number and Incoming Boundary Layer on Shock Boundary Layer Interaction Ilona Stab, James Threadgill, Jesse Little Wall pressure fluctuations, schlieren imaging, oil flow visualization and PIV measurements have been performed on the shock boundary layer interaction (SBLI) formed by a $10^\circ$ compression ramp. The incoming Mach number and boundary layer characteristics are varied to examine their influence on the SBLI. Focus is placed on understanding the effect of these parameters on the structure and unsteadiness of the resultant interaction. Lower Mach numbers $M=2.3$ ($\delta_0=1.7~mm,\;\theta=0.29~mm,\;Re_\theta=3115,\;H=1.4$) and $M=3$ ($\delta_0=1.3~mm ,\;\theta=0.25~mm,\;Re_\theta=1800,\;H=1.8$) show a turbulent or transitional approach boundary layer with no apparent separation at the ramp. Mach~4 has a large separated region which is seemingly a result of a now laminar or transitional approach boundary layer. Pulsations in the separated region correspond to the expected low frequency SBLI dynamics showing a broad peak around a Strouhal number of $St=fL_{int}/U_{\infty}=0.27$ which is lower than the characteristic frequency of the turbulent boundary layer. Additional results examining the influence of boundary layer modifications (e.g. sweep) and wind tunnel side-walls are also included. [Preview Abstract] |
Sunday, November 20, 2016 4:15PM - 4:28PM |
D5.00007: Shock wave boundary layer interaction in jet injection into supersonic crossflow Nithiyaraj Munuswamy, Raghuraman N Govardhan Jet injection into supersonic crossflow results in a bow shock forming upstream of the injected jet. In the present work, we study the unsteady interactions of this shock with the structures in the incoming boundary layer. The studies are done with a sonic air jet injected into a supersonic air crossflow at a Mach number of 2.5 with jet momentum ratios from 1.5 to 3. The interactions of the shock and the incoming boundary layer are measured using PIV in two perpendicular planes, one perpendicular to the wall from which the jet is injected and the other parallel to the wall and within the boundary layer. These measurements enable determination of both structures within the boundary layer, such as low and high speed streaks, and the instantaneous location of the bow shock, in addition to the jet penetration at that instant. The detailed analysis of instantaneous and mean flow quantities for different momentum flux ratios obtained from a large set of instantaneous PIV fields will be presented at the conference. [Preview Abstract] |
Sunday, November 20, 2016 4:28PM - 4:41PM |
D5.00008: Swept Impinging Oblique Shock/Boundary-Layer Interactions Jesse Little, James Threadgill, Ilona Stab, Adam Doehrmann Oblique shock waves impinging on boundary layers are common flow features associated with high-speed flows around complex body geometries and through internal channel flows. The increasingly three-dimensional surface geometries of modern vehicles has led to a prevalence of complex shock/boundary-layer interactions. Sweep has been observed to vary the interaction structure, unsteadinesses, and similarity scalings. Sharp-fins and highly-swept ramps have been noted to induce a quasi-conical development of the interaction, in contrast to a quasi-cylindrical scaling observed in low-sweep interactions. However, swept impinging oblique shock cases have largely been overlooked, with evidence of only cylindrical similarities observed in hypersonic conditions. Flow deflection beyond the maximum turning angle has been proposed as the mechanism for conical interaction development but such behavior has not been established for the present configuration. This study examines the effect of sweep on the interaction induced by a 12.5$^\circ$~generator in Mach~2.3 flow using oil-flow, Schlieren and PIV. Results document the development of similarity scalings at various angles of sweep, and highlight the difficulty in replicating a quasi-infinite span conditions in a moderately sized wind tun [Preview Abstract] |
Sunday, November 20, 2016 4:41PM - 4:54PM |
D5.00009: Contraction ratio effect on boundary layer separation induced by shockwave boundary layer interactions Seongkyun Im, Giovanni Di Cristina, Hyungrok Do Boundary layer separations induced by shockwave boundary layer interaction at various contraction ratios were investigated at a Mach 4.5 flow. Stagnation pressure and temperature condition of 10 bars and 295 K were used, and a high-speed schlieren system visualized the flow features. A shockwave generator with 12 degree wedge generated an impinging shockwave onto a laminar boundary layer on a flat plate. The contraction ratio of the flow was varied by changing the distance between the shockwave generator and the flat plate. The location of the shockwave impingement was fixed while the contraction ratios were changed. Flow visualization showed that the flow separation and its size were influenced by the contraction ratio although overall flow features were similar. At higher contraction ratio, stronger impinging shockwave and more severe flow separation were observed. [Preview Abstract] |
Sunday, November 20, 2016 4:54PM - 5:07PM |
D5.00010: DSMC simulations of leading edge flat-plate boundary layer flows at high Mach number Dr. Sahadev Pradhan The flow over a 2D leading-edge flat plate is studied at Mach number \textit{Ma }$= (U_{inf}/ \backslash $\textit{sqrt\textbraceleft k}$_{B}T_{inf}$\textit{/ m\textbraceright ) }in the range \textit{\textless Ma \textless 10}, and at Reynolds number number \textit{Re }$= (L_{T} U_{inf}$\textit{ rho}$_{inf\thinspace }$\textit{)/ mu}$_{inf\thinspace }$ equal to 10$^{\mathrm{\thinspace \thinspace }}$using two-dimensional (2D) direct simulation Monte Carlo (DSMC) simulations to understand the flow phenomena of the leading-edge flat plate boundary layer at high Mach number. Here, $L_{T}$is the characteristic dimension, $U_{inf}$and $T_{inf}$are the free stream velocity and temperature, \textit{rho}$_{inf}$ is the free stream density, $m$is the molecular mass, \textit{mu}$_{inf\thinspace }$is the molecular viscosity based on the free stream temperature $T_{inf},$and $k_{B}$is the Boltzmann constant. The variation of streamwise velocity, temperature, number-density, and mean free path along the wall normal direction away from the plate surface is studied. The qualitative nature of the streamwise velocity at high Mach number is similar to those in the incompressible limit (parabolic profile). However, there are important differences. The amplitudes of the streamwise velocity increase as the Mach number increases and turned into a more flatter profile near the wall. There is significant velocity and temperature slip ((Pradhan and Kumaran, J. Fluid Mech-2011); (Kumaran and Pradhan, J. Fluid Mech-2014)) at the surface of the plate, and the slip increases as the Mach number is increased. It is interesting to note that for the highest Mach numbers considered here, the streamwise velocity at the wall exceeds the sound speed, and the flow is supersonic throughout the flow domain. [Preview Abstract] |
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