Bulletin of the American Physical Society
72nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 64, Number 13
Saturday–Tuesday, November 23–26, 2019; Seattle, Washington
Session L05: Shock-Boundary Layer Interactions |
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Chair: Leon Vanstone, UT Austin Room: 204 |
Monday, November 25, 2019 1:45PM - 1:58PM |
L05.00001: Low-frequency unsteadiness in a shock wave boundary layer interaction Rio Baidya, Sven Scharnowski, Matthew Bross, Christian J. K\"{a}hler Large field-of-view (FoV) particle image velocimetry experiments are conducted in the vicinity of a shock wave boundary layer interaction (SWBLI) at Mach 2. The current FoV covers up to 30 boundary layer thicknesses, comprising of upstream and downstream regions relative to the SWBLI, thereby allowing the turbulent boundary layer and shock to be simultaneously captured. The relationship between the boundary layer features and the instantaneous shock location is directly quantified, with the aim of better understanding the mechanisms responsible for oscillation of the reflected shock. Simultaneous wall-pressure measurements indicate that the low-frequency fluctuation arising from the oscillating shock foot is not necessarily an independent phenomenon from the turbulent features entering the SWBLI region and interact with the shock. Instead, a large scale separation between their dominant time-scales is due to dampening of high-frequency content beyond the critical frequency of the globally unstable mode occurring at frequencies that are orders of magnitudes slower than the dominant frequency of the very-large-scale velocity features. [Preview Abstract] |
Monday, November 25, 2019 1:58PM - 2:11PM |
L05.00002: Shock-wave boundary layer interactions in an engine intake with a spectral/hp element method. Giacomo Castiglioni, Francesco Montomoli, Spencer J. Sherwin During take off and climbing, i.e. at high angle of attack and high mass flow rate through the engine, the flow on the upper surface of a nacelle bottom lip can develop a region of supersonic flow. The supersonic pocket terminates with a near normal shock-wave which interacts with the incoming boundary layer leading to a shock-wave boundary layer interaction (SWBLI). The aim is to assess the capability of discountinous Galerkin spectral element methods in conjunction with an artificial viscosity shock capturing method to predict the onset of SWBLI unsteadiness in complex geometries relevant to industrial applications. Here it is simulated an experimental rig recently investigated by Coschignano \textit{et al.} The rig is designed around a section of the bottom dead center of a real 3D intake lip; the geometry downstream of the lip is arbitrary and resembles that of an airfoil. Under resolved direct numerical simulations are performed at design conditions which are characterized by an angle of incidence of $23 \deg$ and a free stream Mach number $Ma=0.435$ resulting in a closed, shock-induced, boundary layer separation; the Reynolds number based on lip thickness overlaps the lowest one available experimentally ($Re_L=4\times10^5$). [Preview Abstract] |
Monday, November 25, 2019 2:11PM - 2:24PM |
L05.00003: Shockwave Boundary Layer Interaction Control Using External Forcing from Nanosecond Repetitively Pulsed Dielectric Barrier Discharge Ravichandra Jagannath, Lalit Rajendran, George Schmidt, Tanbo Zhou, Sally Bane The interaction between shock waves and turbulent boundary layers is an interesting phenomenon in high speed aerodynamics. The presence of a shock wave creates an adverse pressure gradient leading to boundary layer separation. This interaction causes unsteadiness in the flow where the separation bubble oscillates at low frequency and the shock oscillates at broadband frequency. The cause of this unsteadiness still remains unanswered. Some results show an upstream influence, while others have shown the downstream separation bubble causing the unsteadiness. This uncertainty in the unsteadiness mechanism makes it difficult to find an ideal location for an active flow control actuator. In the past, plasma jets, localized arc filaments and quasi-DC discharges have been used to control the shock unsteadiness. In this study, a nanosecond repetitively pulsed surface dielectric barrier discharge is used on a 25\textdegree compression corner in Mach 2.5 flow to create an external perturbation in the upstream turbulent boundary layer ahead of the shock wave. The goal is for the external perturbation to be convected downstream and influence the shock oscillation. A combination of schlieren visualization and wall pressure measurements is used to investigate the effect of plasma actuator on shock unsteadiness. The actuator is placed at different locations upstream of the shock to identify the optimal location. The plasma frequency is also varied to identify the optimal frequency for controlling the shock unsteadiness. [Preview Abstract] |
Monday, November 25, 2019 2:24PM - 2:37PM |
L05.00004: Analysis of the effect of elasticity on Shock Turbulent Boundary Layer Interaction Jonathan Hoy, Ivan Bermejo-Moreno The effect of elasticity on the unsteady behavior of a shock-turbulent boundary layer interaction (STBLI) is investigated through the use of a coupled fluid structure interaction (FSI) solver which incorporates a wall-modeled large eddy simulation (WMLES) finite-volume flow solver, an undamped finite-element solid mechanics solver, and a mesh deformation solver based on a fictitious spring-system which calculates the change in flow domain mesh geometry as it is deformed by the solid domain. The FSI solver is validated through comparison to the experimental work of Willems et al (2016) and to the LES simulations of Pasquariello et al (2015). In these cases, a supersonic flow at Mach 3 is deflected downward by 20 degrees to create an oblique shock wave that impinges on the turbulent boundary layer developed over a flexible elastic panel (with a Reynolds number of 205,000 based on the boundary layer thickness upstream of the interaction). Parametric studies are then performed to investigate the impact of panel vibration on the STBLI and separation bubble dynamics, varying the panel natural frequencies and shock strength. [Preview Abstract] |
Monday, November 25, 2019 2:37PM - 2:50PM |
L05.00005: Mean and Unsteady Characteristics of Swept SBLIs Sathyan Padmanabhan, Jorge Castro Maldonado, James Threadgill, Jesse Little An experimental study has been conducted on swept impinging oblique shock turbulent boundary layer interactions (SBLIs) generated by $12.5^\circ$ shock generators at various sweep angles in Mach 2.3 flow. Mean and unsteady features are examined using oil flow visualization, mean pressure measurements, and high bandwidth pressure transducers. Mean results show the flow is fully separated, and for higher sweep angles, exhibits a spanwise growth of the interaction, displaying a conical behavior away from the inception region. Unsteady pressure measurements reveal low-frequency unsteadiness along the separation shock foot, with reduced amplitude in comparison to similar strength unswept interactions. Separation shock motion is coherent along the span in lower frequencies while spanwise traveling ripples present in the shock foot accelerate from the root towards the tip over the range of 15-25\% of $U_\infty$. Minor correlation is observed between shock motion and pressure disturbances directly upstream in the incoming boundary layer, but this becomes negligible when offset in the spanwise direction. This suggests that shock rippling is not driven by upstream disturbances, but instead associated with a time scale inherent to the interaction. [Preview Abstract] |
Monday, November 25, 2019 2:50PM - 3:03PM |
L05.00006: Structure and Unsteadiness of Shock-foot and Separation Location in a Swept SBLI at Mach 2 Leon Vanstone, Mustafa Musta, Noel Clemens This study examined the structure and unsteadiness of a 3D shock wave / boundary layer interaction (SBLI) generated by a swept compression ramp in a Mach 2 flow. Fast response PSP was used to examine the behavior of the separation shock foot unsteadiness and high frequency PIV data was used to examine the separation line unsteadiness. Shock-foot unsteadiness was broadband, having significant low- (St<0.01), mid- (0.01< St< 0.10), and high-frequency (St> 0.10) content. Generally, the shock foot contained lower frequency content in comparison to the separation line. In a low-frequency band the behavior of the shock foot was similar to that of the separation line. The mid- and high-frequency band shock-foot unsteadiness was not characteristically similar to the separation location. Many studies examine SBLI unsteadiness using only a single characterising feature (shock foot, separation line, etc.). Our results showed that the shock and separation lines have different characteristic behavior. Hence, different features within the SBLI give different characteristic impressions of unsteadiness. [Preview Abstract] |
Monday, November 25, 2019 3:03PM - 3:16PM |
L05.00007: Root Influence on Swept Impinging Oblique Shock Boundary Layer Interactions Jorge Castro Maldonado, Sathyan Padmanabhan, James Threadgill, Jesse Little Shock boundary layer interactions (SBLIs) are ubiquitous in internal and external supersonic flows. Detrimental effects include structural fatigue through unsteady pressure loading and high aerothermal stresses. An understanding of swept (3D) interactions is lacking compared to their unswept (2D) counterparts. To this end, the effect of disturbances induced by a microramp at the root region of a swept SBLI is investigated. Experiments are conducted at a nominal Mach number of 2.3 with a fully turbulent boundary layer ($Re_{\theta}$ = $5.5 \times 10^{3}$). Previous investigations show unsteady shock motion with constant frequencies across the spanwise domain. To determine if this frequency content is associated with the root structure, the length scale of root separation is altered by installing a microramp of height 0.3$\delta_{0}$, placed 15$\delta_{0}$ upstream of the root inviscid shock impingement location. Preliminary oil flow visualization shows no significant differences on the mean flow topology away from the root, enabling direct comparisons between the baseline and perturbed unsteady behavior. Mean and unsteady wall pressures are captured to assess changes in pressure distribution and associated spectral content, gaining valuable insight into the underlying physics. [Preview Abstract] |
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