Bulletin of the American Physical Society
71st Annual Meeting of the APS Division of Fluid Dynamics
Volume 63, Number 13
Sunday–Tuesday, November 18–20, 2018; Atlanta, Georgia
Session E21: Boundary Layers: General |
Hide Abstracts |
Chair: Jonathan Morrison, Imperial College London Room: Georgia World Congress Center B309 |
Sunday, November 18, 2018 5:10PM - 5:23PM |
E21.00001: Identifying the turbulent-boundary-layer interface in a transitional flow using a self-organizing map Zhao Wu, Jin Lee, Charles Vivant Meneveau, Tamer A Zaki An unsupervised machine-learning algorithm, the self-organizing map (SOM), is used to identify the turbulent boundary layer (TBL) and non-TBL regions in bypass transition. The data employed for the analysis are from an archived direct simulation publicly available in the Johns Hopkins Turbulence Databases (JHTDB, http://turbulence.pha.jhu.edu), stored using the new FileDB system. The data points in the entire flow domain are automatically classified into TBL and non-TBL regions by the SOM, based on their standardized velocity, velocity fluctuations, velocity gradients and their spatial locations. Thus the SOM identifies the turbulent-boundary-layer interface (TBLI) without the usual need for choosing thresholds on e.g. vorticity or velocity fluctuations. The TBLI is found to be a hyperplane in the input space. The SOM distinguishes the streaks in the laminar region and the weak free-stream turbulence from TBL region. Results from our approach are shown to be consistent with threshold-based methods in the special cases when those are applicable. |
Sunday, November 18, 2018 5:23PM - 5:36PM |
E21.00002: Study of thin film carbon nanotubes as thermo-acoustic transition control actuators David Thomas Booth This experiment explored the feasibility of thin film carbon nanotubes (CNT) thermo-acoustic actuators as a way of active transition control of boundary layers on a flat plate. The device works by sending waves of heat and sound through the boundary layer at a specific frequency and phase with the goal of interacting with Tollmien-Schlichting (T-S) waves. A wind tunnel boundary layer plate experiment was designed that consists of a flat plate with an elliptical leading edge, adjustable trailing edge flap, and two sets of CNT actuators mounted on the surface. Actuators were located at two streamwise locations in the laminar region of the flat plate. The free-stream velocity was U = 16 m/s for comparison with other T-S wave results. Actuators were operated at 250Hz to specifically target the T-S wave instability at this flow velocity. A PIV system was used to detect and measure velocity fluctuations caused by the presence of T-S waves. Time and phase averaged PIV measurements were acquired at four downstream interrogation domains with the upstream actuator operating over a range of actuator power settings. The effectiveness of CNT actuators as T-S wave exciters was evaluated and will be discussed. |
Sunday, November 18, 2018 5:36PM - 5:49PM |
E21.00003: Inner-outer interaction in a Rapidly Sheared Boundary Layer (RSBL). Jonathan F Morrison, Sourabh S Diwan We present results from an experiment in which grid-generated turbulence is passed initially over a moving ground plane to create a shearless boundary layer, which is then rapidly sheared as it encounters a stationary surface downstream. Close to the leading edge of the stationary surface, the conditions of the Rapid Distortion Theory (RDT) can be expected to be approximately satisfied. We report measurements of both velocity and pressure in the RSBL: the spectra of the streamwise velocity fluctuations display a bi-modal shape, resembling those in an equilibrium turbulent boundary layer. The streamwise evolution of the spectra indicates that the low-wavenumber peak in the spectra indicate a 'top-down' mechanism, whereas the relatively high-wavenumber part of the spectrum can be attributed to a 'bottom-up' mechanism. Static pressure fluctuations measured using a needle probe show that their correlation with the wall pressure is much higher in the RSBL, compared to a canonical layer, especially close to the leading edge of the stationary surface. This implies that the pressure fluctuations near the boundary-layer edge are strongly coupled with those in the near-wall region. The further implications are discussed. |
Sunday, November 18, 2018 5:49PM - 6:02PM |
E21.00004: Localized influence of Langmuir supercells on turbulence in shallow water Bing-qing Deng, Anqing Xuan, Zixuan Yang, Lian Shen In shallow water, Langmuir supercells generated by the interaction between surface water waves and wind-driven shear turbulence are pairs of counter-rotating streamwise vortices that can engulf the whole water column. Because Langmuir supercells can exist for long time at a fixed location, they can greatly influence the distribution of turbulence. In this study, we performed wall-resolved large-eddy simulations of Langmuir turbulence in shallow water based on the C-L equations to investigate the localized influence of Langmuir supercells on turbulence. The distributions of the Reynolds stresses contributed by turbulence are analyzed. The underlying mechanism for the localized influence is analyzed based on the budgets of the Reynolds stresses contributed by turbulence. The relationship between the intensities of the localized Reynolds stresses and the Langmuir supercells is elucidated. |
Sunday, November 18, 2018 6:02PM - 6:15PM |
E21.00005: Robust features of a turbulent boundary layer subjected to free-stream turbulence R. Jason Hearst, Eda Dogan, Bharathram Ganapathisubramani We use an active grid to generate high-intensity free-stream turbulence with 7.2% ≤ u’∞/U∞ ≤ 13.0% and 302 ≤ Reλ ≤ 760, and study the impact these varying conditions have on a turbulent boundary layer. In particular, several cases are produced with fixed turbulence intensities and Reynolds numbers, but up to a 65% change in the integral scale. Qualitatively the spectra at various wall-normal positions in the boundary layer look similar, however, there are quantifiable differences at the large wavelengths all the way to the wall. It is also demonstrated that longitudinal statistics up to fourth-order are well collapsed at a given u’∞/U∞, regardless of the other free-stream turbulence parameters. Perhaps the most interesting feature of these flows is that the outer spectral peak appears to be governed by a set of global scaling laws while the near-wall spectral peak is independent of the free-stream conditions. This allows us to build a model whereby we can determine the entire pre-multiplied spectrogram a priori, and in particular know the location and magnitude of the spectral peaks to within 6% with only knowledge of the free-stream spectrum, the boundary layer height, and the friction velocity. |
Sunday, November 18, 2018 6:15PM - 6:28PM |
E21.00006: Detection and characterization of very-large-scale motions in the atmospheric surface layer through wind LiDAR measurements Giacomo Valerio Iungo, Behzad Najafi, Matteo Puccioni Coherent turbulent structures with dimensions larger than the height of the atmospheric surface layer (ASL), h, denoted as very-large-scale motions (VLSMs) or superstructures, have been investigated through scanning Doppler wind LiDARs. Measurements were performed at two sites: one very flat and homogeneous at the SLTEST facility, Utah, and a second site in Celina, Texas, which is characterized by a certain level of heterogeneity and an aerodynamic roughness length of two orders of magnitude larger than for the first site. LiDAR measurements were performed using a probe-volume with a length of 18 m, which leads to a vertical resolution smaller than 1 m. Pre-multiplied velocity spectra of the LiDAR data singled out the presence of an energy peak at an altitude about 0.15 h associated with wavelengths about 4-10 h. Integral length scales, aspect ratio and inclinations of VLSMs are estimated as well, which are in good agreement with previous experiments. The results indicate that current wind LiDAR technology is a valuable measurement technique to investigate VLSMs, while providing easier deployments than traditional towers and allowing for custom scanning strategies to probe the entire ASL height. |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700