Bulletin of the American Physical Society
68th Annual Meeting of the APS Division of Fluid Dynamics
Volume 60, Number 21
Sunday–Tuesday, November 22–24, 2015; Boston, Massachusetts
Session L21: Turbulence: Compressible Boundary Layers and Jets |
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Chair: Steven Beresh, Sandia National Laboratories Room: 209 |
Monday, November 23, 2015 4:05PM - 4:18PM |
L21.00001: Log-law and compressibility effects in transcritical turbulent boundary layers at supercritical pressure Soshi Kawai In this talk, we discuss the log-law and effects of compressibility in transcritical heated turbulent boundary layers on a zero-pressure-gradient flat plate at supercritical pressure conditions by solving the compressible Navier-Stokes equations using direct numerical simulation. In the supercritical fluids (especially at transcritical conditions), due to the strong real fluid effects thermodynamic properties vary abruptly within a narrow temperature range through the pseudo-critical temperature and significantly deviate from the ideal fluid. Peculiar interactions between the strongly non-linear real fluid effects and wall turbulence, and its resultant log-law and turbulence statistics are discussed, which have never been seen in the ideal-fluid turbulent boundary layers. We also show non-negligible compressibility effects in the flow even in the low-Mach number regime considered in this study. [Preview Abstract] |
Monday, November 23, 2015 4:18PM - 4:31PM |
L21.00002: Turbulent Eddies in a Compressible Jet in Crossflow Measured using Pulse-Burst PIV Steven Beresh, Justin Wagner, John Henfling, Russell Spillers, Brian Pruett Pulse-burst Particle Image Velocimetry (PIV) has been employed to acquire time-resolved data at 25 kHz of a supersonic jet exhausting into a subsonic compressible crossflow. Data were acquired along the windward boundary of the jet shear layer and used to identify turbulent eddies as they convect downstream in the far-field of the interaction. Eddies were found to have a tendency to occur in closely-spaced counter-rotating pairs and are routinely observed in the PIV movies, but the variable orientation of these pairs makes them difficult to detect statistically. Correlated counter-rotating vortices are more strongly observed to pass by at a larger spacing, both leading and trailing the reference eddy. This indicates the paired nature of the turbulent eddies and the tendency for these pairs to convect through the field of view at repeatable spacings. Velocity spectra reveal a peak at a frequency consistent with this larger spacing between shear-layer vortices rotating with identical sign. Super-sampled velocity spectra to 150 kHz reveal a power-law dependency of -5/3 in the inertial subrange as well as a -1 dependency at lower frequencies attributed to the scales of the dominant shear-layer eddies [Preview Abstract] |
Monday, November 23, 2015 4:31PM - 4:44PM |
L21.00003: Development of turbulent variable density mixing in jets with coflow John Charonko, Kathy Prestridge Fully turbulent jets with coflow at two density ratios (At=0.1 \& 0.6) were studied as a statistically stationary system for improving our understanding of variable density mixing in turbulent flows. The exit Reynolds number was matched for both flows at $\sim$19,000 and simultaneous planar PIV and acetone PLIF measurements were acquired so the coupled evolution of the velocity and density statistics could be examined in terms of density-weighted average quantities. Measurements were taken over 10,000 snapshots of the flow at three locations to insure statistical convergence, and the spatial resolution (288 $\mu$m) was at or below the Taylor microscale. In agreement with our previous work at lower Reynolds numbers, for large density ratios turbulent kinetic energy and Reynolds stresses are preserved or increased with downstream distance, contrasting with the behavior at low density ratios. Furthermore, in regions where the buoyancy effects began dominating the initial momentum-driven flow ($\sim$30 jet diameters), the jet is still not developing toward a self-similar state. Instead, a region of homogeneous turbulence appeared to establish itself in the center of the jet even for the lower density ratio condition, in contrast with classical results for single-fluid jets. [Preview Abstract] |
Monday, November 23, 2015 4:44PM - 4:57PM |
L21.00004: Identifying Coherent Structures in a 3-Stream Supersonic Jet Flow using Time-Resolved Schlieren Imaging Andrew Tenney, Thomas Coleman, Matthew Berry, Andy Magstadt, Sivaram Gogineni, Barry Kiel Shock cells and large scale structures present in a three-stream non-axisymmetric jet are studied both qualitatively and quantitatively. ~Large Eddy Simulation is utilized first to gain an understanding of the underlying physics of the flow and direct the focus of the physical experiment. ~The flow in the experiment is visualized using long exposure Schlieren photography, with time resolved Schlieren photography also a possibility. ~Velocity derivative diagnostics are calculated from the grey-scale Schlieren images are analyzed using continuous wavelet transforms. ~Pressure signals are also captured in the near-field of the jet to correlate with the velocity derivative diagnostics and assist in unraveling this complex flow.~~~We acknowledge the support of AFRL through an SBIR grant. [Preview Abstract] |
Monday, November 23, 2015 4:57PM - 5:10PM |
L21.00005: Hydro-acoustic instabilities in compressible turbulent channel flow with porous walls Carlo Scalo, Iman Rahbari C. Scalo, J. Bodart, and S. K. Lele, Phys. Fluids (2015) manipulated wall-bounded compressible turbulence by applying impedance boundary conditions (IBC) acoustically tuned to the characteristic time scale of the large-scale eddies. Near-wall turbulence was overhauled by hydro-acoustic instabilities -- comprised of coherent spanwise Kelvin-Helmholtz rollers driven by Helmholtz-like acoustic resonance -- while outer-layer turbulence was left structurally unaltered. We discuss linear modeling results of the observed flow response, supported by new high-fidelity simulations up to transonic bulk Mach numbers. For IBCs with zero reactance, corresponding to a Darcy-like formulation for porous walls, two dominant modes are identified whose Reynolds stress distributions overlap with the impermeable-wall turbulent buffer layer, directly affecting the near-wall turbulence cycle. For the range of wavenumbers investigated, the transition from subcritical to supercritical permeability does not significantly alter the structure of the unstable modes, showing that wall-permeability accentuates pre-existing, otherwise stable, modes. Implications on flow control strategies for compressible boundary layers over porous walls are discussed. [Preview Abstract] |
Monday, November 23, 2015 5:10PM - 5:23PM |
L21.00006: Geometric invariance of compressible turbulent boundary layers Wei-Tao Bi, Bin Wu, Zhen-Su She, Fazle Hussain A symmetry based approach is applied to analyze the mean velocity and temperature fields of compressible, flat plate turbulent boundary layers (CTBL). A Reynolds stress length scale and a turbulent heat flux length scale are identified to possess the same defect scaling law in the CTBL bulk, which is solely owing to the constraint of the wall to the geometry of the wall-attached eddies, but invariant to compressibility and wall heat transfer. This invariance is called the geometric invariance of CTBL eddies and is likely the origin of the Mach number invariance of Morkovin's hypothesis, as well as the similarity of energy and momentum transports. A closure for the turbulent transport by using the invariant lengths is attainted to predict the mean velocity and temperature profiles in the CTBL bulk- superior to the van Driest transformation and the Reynolds analogy based relations for its sound physics and higher accuracy. Additionally, our approach offers a new understanding of turbulent Prandtl number. [Preview Abstract] |
Monday, November 23, 2015 5:23PM - 5:36PM |
L21.00007: A symmetry based approach to quantifying the compressible turbulent boundary layer Bin Wu, Wei-Tao Bi, Zhen-Su She, Fazle Hussain Developing analytical description of the compressible turbulent boundary layer (CTBL) is of great importance to many technological applications and to the understanding and modeling of compressible turbulence. Here a symmetry-based approach is applied to analyze the CTBL data acquired from DNS, covering a wide range of Reynolds number (\textit{Re}), Mach number (\textit{Ma}) and wall temperature. The Reynolds stress length scale displays a four-layer structure in the direction normal to the wall and obeys the dilation group invariance as in the incompressible TBL. A newly-identified turbulent heat flux length scale behaves similarly, which is the classical temperature mixing length weighted by the mean temperature. A significant result is the identification of three physical parameters for each length function to characterize the adiabatic flow: a bulk flow constant, a buffer layer thickness and a boundary layer edge, which vary with \textit{Re} and \textit{Ma}. For the diabatic flow, the sublayer thickness and the inner layer scaling exponents vary additionally with the wall temperature. These parameters are modeled empirically, leading to a highly accurate prediction of the mean fields of the CTBL. Thus we reveal that the symmetry principle found in canonical wall-bounded flows holds also for the CTBL, and a quantitative mean field theory is viable with appropriate symmetry considerations. [Preview Abstract] |
Monday, November 23, 2015 5:36PM - 5:49PM |
L21.00008: Effect of Pulsed Plasma Jets on the Recovering Boundary Layer Downstream of a Reflected Shock Interaction Benton Greene, Noel Clemens, Patrick Magari, Daniel Micka, Mattheus Ueckermann Shock-induced turbulent boundary layer separation can have many detrimental effects in supersonic inlets including flow distortion and instability, structural fatigue, poor pressure recovery, and unstart. The current study investigates the effect of pulsed plasma jets on the recovering boundary layer downstream of a reflected shock wave-boundary layer interaction. The effects of pitch and skew angle of the jet as well as the heating parameter and discharge time scale are tested using several pulsing frequencies. In addition, the effect of the plasma jets on the undisturbed boundary layer at 6 mm and 11 mm downstream of the jets is measured. A pitot-static pressure probe is used to measure the velocity profile of the boundary layer 35 mm downstream of the plasma jets, and the degree of boundary layer distortion is compared between the different models and run conditions. Additionally, the effect of each actuator configuration on the shape of the mean separated region is investigated using surface oil flow visualization. Previous studies with lower energy showed a weak effect on the downstream boundary layer. The current investigation will attempt to increase this effect using a higher-energy discharge. [Preview Abstract] |
Monday, November 23, 2015 5:49PM - 6:02PM |
L21.00009: Acoustic Radiation from a Mach 14 Turbulent Boundary layer Chao Zhang, Lian Duan, Meelan Choudhari Direct numerical simulations (DNS) are used to examine the pressure fluctuations generated by a high-speed turbulent boundary layer with a nominal freestream Mach number of 14 and wall temperature of 0.18 times the recovery temperature. The emphasis is on characterizing the acoustic radiation from the turbulent boundary layer and comparing it with previous simulations at Mach 2.5 and Mach 6 to assess the Mach-number dependence of the freestream pressure fluctuations. In particular, the numerical database is used to provide insights into the pressure disturbance spectrum and amplitude scaling with respect to the freestream Mach number as well as to understand the acoustic source mechanisms at very high Mach numbers. Such information is important for characterizing the freestream disturbance environment in conventional (i.e., noisy) hypersonic wind tunnels. Spectral characteristics of pressure fluctuations at the surface are also investigated. [Preview Abstract] |
Monday, November 23, 2015 6:02PM - 6:15PM |
L21.00010: Investigation of Shock-Induced Laminar Separation Bubble in a Supersonic Boundary Layer Jayahar Sivasubramanian, Hermann Fasel The interaction between an impinging oblique shock and a laminar boundary-layer on a flat plate is investigated using DNS. In particular, the two-dimensional separation bubble resulting from the shock/boundary-layer interaction (SBLI) at freestream Mach number of 2.0 is investigated in detail. The flow parameters used for the present investigation match the laboratory conditions in the experiments by Hakkinen {\it{et al.}} The skin friction and pressure distribution from the simulations are compared to the experimental measurements and numerical results available in the literature. Our results confirm the asymmetric nature of the separation bubble as reported in the literature. In addition to the steady flow field calculations, the response to low-amplitude disturbances is investigated in order to study the linear stability behavior of the separation bubble. For comparison, both the development of two-dimensional and three-dimensional (oblique) disturbances are studied with and without the impinging oblique shock. Furthermore, the effects of the shock incidence angle and Reynolds number are also investigated. Finally, three-dimensional simulations were performed in order to explore the laminar-turbulent transition process in the presence of a laminar separation bubble. [Preview Abstract] |
Monday, November 23, 2015 6:15PM - 6:28PM |
L21.00011: MOVED TO D4.010 |
Monday, November 23, 2015 6:28PM - 6:41PM |
L21.00012: Investigation of corner shock boundary layer interactions to understand inlet unstart Morgan Funderburk Inlet unstart is a detrimental phenomenon in dual-mode ramjet/scramjet engines that causes severe loss of thrust, large transient structural load, and potentially a loss of the aircraft. In order to analyze the effects that the corner shock boundary layer interaction (SBLI) has on initiating and perpetuating inlet unstart, a qualitative and quantitative investigation into mean and dynamic features of corner SBLI at various Mach numbers is made. Surface streakline visualization showed that the corner SBLI is highly three-dimensional with a dominant presence of corner separation vortex. Further, the peak r.m.s. pressure was located at the periphery of corner separation vortex, suggesting that the unsteady loading is caused by the corner vortex. Power spectral densities of wall-pressure fluctuations in the peak r.m.s. location were analyzed in order to characterize the dominant frequencies of oscillation of the flow structures and to unravel the dynamic interactions between them in order to expand the operating margin of future hypersonic air breathing vehicles. [Preview Abstract] |
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