Bulletin of the American Physical Society
64th Annual Meeting of the APS Division of Fluid Dynamics
Volume 56, Number 18
Sunday–Tuesday, November 20–22, 2011; Baltimore, Maryland
Session M7: Turbulent Boundary Layers VII: High Re/Mach Nos. |
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Chair: Pino Martin, University of Maryland Room: 310 |
Tuesday, November 22, 2011 8:00AM - 8:13AM |
M7.00001: Well resolved pipe flow measurements at extreme Reynolds numbers Margit Vallikivi, Marcus Hultmark, Sean Bailey, Alexander Smits Statistics of the streamwise velocity component were measured at Reynolds numbers ranging from $Re_{\tau}=1\times10^3$ to $Re_{\tau}=1\times10^5$ in fully-developed pipe flow. Pipes with two different surface finishes were studied, allowing a comparison between high Reynolds numbers turbulence in the hydraulically smooth and rough regimes. For better spatial resolution a nano- scale thermal anemometry probe (NSTAP) was used to acquire the data. The data gives new insight on pipe flow turbulence at extremely high Reynolds numbers, showing no interaction between the inner and the outer layer. The results also show a Reynolds number dependent outer peak in the turbulent fluctuations, which is only evident at very high Reynolds numbers. These extremely high Reynolds numbers reveal that the scaling of the fluctuations is much more similar to that of the mean velocities than previously believed. [Preview Abstract] |
Tuesday, November 22, 2011 8:13AM - 8:26AM |
M7.00002: Turbulence Spectra in High Reynolds Number Pipe Flow Brian Rosenberg, Marcus Hultmark, Margit Vallikivi, Alexander Smits Streamwise velocity spectra are acquired in fully-developed turbulent pipe flow over two decades of Reynolds number. Highly-resolved measurements are made possible by using a nano-scale thermal anemometry probe. We address the existence and nature of the classical $k^{-1}$ and $k^{-5/3}$ spectral regions as well as the behavior of the very-large-scale motions (VLSM). The wall-normal variation of the VLSM spectral peak suggests that these motions originate at the boundary and grow with increasing wall distance, which stands in contrast to the outer-scaling behavior of boundary layer superstructures. This mechanism implies that in pipe flows outer- and inner- layer motions do not interact significantly, which was first seen in the behavior of the turbulence intensity. [Preview Abstract] |
Tuesday, November 22, 2011 8:26AM - 8:39AM |
M7.00003: Zero pressure gradient boundary layer at extreme Reynolds numbers Marcus Hultmark, Margit Vallikivi, Alexander Smits Experiments were conducted in a zero pressure gradient flat plate boundary layer using the Princeton/ONR High Reynolds number Test Facility (HRTF). The HRTF uses highly compressed air, up to 220 atmospheres, to produce Reynolds numbers up to $Re_{\theta}=225,000$. This corresponds to a $\delta^+=65,000$ which is one of the highest Reynolds numbers ever measured in a laboratory. When using pressure to achieve high Reynolds numbers the size of the measurement probes become critical, thus the need for very small sensors is acute. The streamwise component of velocity was investigated using a nanoscale thermal anemometer (NSTAP) as well as a $200\mu m$ pitot tube. The NSTAP has a spatial resolution as well as a temporal resolution one order of magnitude better than conventional measurement techniques. The data was compared to recent data from a high Reynolds number turbulent pipe flow and it was shown that the two flows are more similar than previous data suggests. [Preview Abstract] |
Tuesday, November 22, 2011 8:39AM - 8:52AM |
M7.00004: Turbulence in a Hypersonic Boundary Layer Owen Williams, Alexander Smits Turbulent fluctuations in hypersonic boundary layers are conventionally collapsed using Morkovin scaling which has been shown to be broadly applicable up to Mach numbers as high as 5. To validate Morkovin's hypothesis at higher Mach numbers, and help improve our understanding of hypersonic wall-bounded turbulence, we report PIV measurements of two components of velocity fluctuations in a flat plate, turbulent boundary layer at Mach 7.4 in a perfect gas, at a Reynolds number based on momentum thickness of about 3500. Multiple tripping methods were evaluated to establish the sensitivity of the flow to initial conditions. Validation of the PIV results will be discussed and comparisons of various turbulent quantities will be made with DNS under identical flow conditions. [Preview Abstract] |
Tuesday, November 22, 2011 8:52AM - 9:05AM |
M7.00005: Direct Numerical Simulation of Turbulent Boundary Layers on a Large Domains Yin-Chiu Kan, Clara Helm, Izaak Beekman, Pino Martin Direct numerical simulation data of spatially-developing subsonic, supersonic and hypersonic turbulent boundary layers with matching similarity parameters are presented. The simulations are performed on large computational domains, using the rescaling technique with large rescaling lengths to minimize numerical correlation of the inflow and recycling planes. The simulations are run for long times without forcing the artificial acoustic modes in the free stream. We investigate the evolution of the boundary layer parameters and basic statistics with streamwise distance through the computational box and examine the turbulence structure through spectral analysis and filtered instantaneous flow fields. We pay special attention to the largest structures, with turbulence modeling, especially aspects unique to compressible boundary layers, in mind. [Preview Abstract] |
Tuesday, November 22, 2011 9:05AM - 9:18AM |
M7.00006: DNS of a Mach 7.2 turbulent boundary layer over square bar roughness elements Izaak Beekman, Pino Martin The direct numerical simulation of a turbulent, Mach 7.2 boundary layer over two-dimensional, square-bar roughness elements is presented. The physics of this flow are discussed, especially their similarities and differences with respect to compressible, smooth-wall, flat-plate boundary layers. Some interesting similarities exist, including the presence of near wall spanwise coherent structures and possible evidence of hairpin-packets. Additionally, the turbulence is characterized in terms of structure and statistics. The simulation technique and the challenges therein are also discussed, as the violent nature of the near wall region and the formation of transient shocks on the roughness elements makes this a challenging flow to study. [Preview Abstract] |
Tuesday, November 22, 2011 9:18AM - 9:31AM |
M7.00007: Turbulence in supersonic boundary layers at moderate Reynolds number Sergio Pirozzoli, Matteo Bernardini We study the organization of turbulence in supersonic boundary layers through direct numerical simulations at $M_{\infty}=2$, $200 \le Re_{\tau} \le 1120$. Comparison of the velocity statistics up to fourth order shows collapse on reference incompressible data, provided the mean velocity and the velocity fluctuations are scaled to incorporate the effects of mean density variation, as postulated by Morkovin's hypothesis. Strict wall scaling is lost at high Reynolds for the ``attached'' flow variables, whose inner peak is found to increase with $Re_{\tau}$. The modifications of the structure of the flow field that underlie this change of behavior are highlighted through flow visualizations, which substantiate the formation of large jet-like and wake-like motions in the outer part of the boundary layer, which extend their influence to the near-wall region. It is found that the typical size of the attached eddies roughly scales with the local mean velocity gradient, rather than being proportional to the wall distance, as dictated by the attached eddy hypothesis. The interactions of the large eddies in the outer layer with the near-wall region are quantified through the two-point amplitude modulation covariance, which characterizes the modulating action of energetic outer-layer eddies on other points in the same streamwise/wall-normal plane. [Preview Abstract] |
Tuesday, November 22, 2011 9:31AM - 9:44AM |
M7.00008: Spatial Correlation in the Fluctuating Wall Pressure Field Beneath a Supersonic Turbulent Boundary Layer Steven Beresh, John Henfling, Russell Spillers, Brian Pruett Data have been acquired from a spanwise array of fluctuating wall pressure sensors beneath a wind tunnel wall boundary layer at Mach 2, then invoking Taylor's Hypothesis allows the temporal signals to be converted into a spatial map of the wall pressure field. Different frequency ranges of pressure fluctuations may be accessed by bandpass filtering the signals. This reveals signatures of coherent structures where negative pressure events are interspersed amongst positive events, with some degree of alternation in the streamwise direction. Within lower frequency ranges, streaks of instantaneously correlated pressure fluctuations elongated in the streamwise direction exhibit a spanwise meander and show apparent merging of pressure events, resembling similar structures known to exist in the velocity field. However, the pressure data lack the spanwise quasi-periodicity of positive and negative events found in velocity data, and conversely demonstrate a weak positive correlation in the spanwise direction whose extent increases at lower frequencies. The occasional passage of coherent structures spanning the entire sensor array provides an explanation for the weak spanwise correlations, a phenomenon not noted in velocity fields. [Preview Abstract] |
Tuesday, November 22, 2011 9:44AM - 9:57AM |
M7.00009: Roughness Induced transition in supersonic boundary layers Suman Muppidi, Krishnan Mahesh Laminar-to-turbulent transition at high speeds can significantly alter aerodynamic drag and heat transfer. The present study uses Direct Numerical Simulations to study transition of a Mach 2.9 boundary layer due to distributed surface roughness. Roughness causes the near-wall fluid to slow down and generates a strong shear layer over the roughness elements. Roughness surface also exerts an upward impulse on the fluid, generating counter-rotating pairs of streamwise vortices underneath the shear layer. As they move downstream, these vortices rise toward the shear layer, and their mutual interaction results in the break down of the shear layer, followed closely by transition to turbulence. The mean flow in the turbulent region shows a good agreement with available data for fully turbulent boundary layers. Simulations under varying conditions show that where the shear layer is not as strong, and the streamwise vortices are not as coherent, the flow remains laminar. [Preview Abstract] |
Tuesday, November 22, 2011 9:57AM - 10:10AM |
M7.00010: DSN at High Reynolds numbers of Thermal Turbulent Boundary Layers Subject to External Pressure Gradient Luciano Castillo, Guillermo Araya Direct Numerical Simulations (DNS) of thermal spatially evolving boundary layers at zero (ZPG), favorable (FPG) and adverse (APG) pressure gradients are performed. The range for the momentum thickness Reynolds number, $Re_\theta$, varies from 300 up to 3000. The predicted skin friction coefficient and Stanton number show fairly good agreement with empirical correlations, experimental and numerical data from the literature. The effects of the Reynolds number and streamwise adverse pressure gradient on the flow and thermal parameters are also explored and visualized. Additionally, the location of the maximum thermal fluctuations in outer coordinates moves closer to the wall as the Reynolds number increases. It was confirmed that the principal effects of adverse pressure gradient on the flow were the appearance of peaks, particularly on the streamwise velocity fluctuations, in the outer region. Furthermore, as the Reynolds number increases, the location of the maximum thermal fluctuations moved closer to the wall when plotted in outer coordinates. Finally, the observed correlation between streamwise velocity and thermal fluctuations in ZPG flows disappears in Strong APG flows. [Preview Abstract] |
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