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 D38: Flow Instability: Boundary Layers I |
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Chair: Yu Nishio, Tohoku University Room: Sheraton Back Bay B |
Sunday, November 22, 2015 2:10PM - 2:23PM |
D38.00001: Experimental Study of Leading Edge Receptivity to Freestream Local Disturbance Yu Nishio, Tomonari Oka, Seiichiro Izawa, Yu Fukunishi Leading edge receptivity of a flat plate is investigated in a wind tunnel experiment. Sheet-jet type velocity fluctuations are introduced into the freestream using a wing-shaped disturbance generator installed upstream of the plate. Steady or pulsating jet is ejected from the generator filling the velocity deficit of the generator body. So the device generates velocity fluctuations without changing the velocity profile. Whether the generated velocity fluctuations affect the growth of fluctuations inside boundary layer is examined in detail. When the generator is placed at the same height as the stagnation point of the leading edge, the velocity fluctuations taken into the boundary layer just monotonically decay. On the other hand, when the generator is placed slightly higher than the stagnation point level, the velocity fluctuations inside the boundary layer tentatively grow showing higher receptivity, which gradually decay downstream. The strength of the velocity fluctuations inside the boundary layer are related to the velocity fluctuations outside the boundary layer. The effects of pulsating the jet are limited in both experiments. [Preview Abstract] |
Sunday, November 22, 2015 2:23PM - 2:36PM |
D38.00002: Biglobal stability analysis of spatially developing axisymmetric boundary layers Vinod Narayanan, Ramesh Bhoraniya Global stability analysis of incompressible axisymmetric boundary layers is performed. In the present analysis, we consider two geometries; axial flow over circular cylinders and circular cones. The Bi-global stability equations together with the boundary conditions form an eigenvalues problem and are solved using Arnoldi's algorithm. Chebyshev spectral collocation method is used for discretization of the stability equations. Spatial growth rate of disturbance waves at different Reynolds numbers and azimuthal wave numbers are computed. The results show that the disturbances have non-wave like behavior. The normalized spatial amplification in streamwise direction increases with increase in Reynolds number for axisymmetric mode. However, for non-axisymmetric modes it reduces with increase in Reynolds number. In case of flow over circular cone, stability analysis is performed for different cone angles, range of Reynolds numbers and different azimuthal wave numbers. The disturbances do not show wavelike behavior in this too. The flow is found to be spatially destabilizing in the case of circular cones at low Reynolds numbers. Thus the effect of transverse curvature here is destabilizing the flow. Detailed results will be presented at the time of conference. [Preview Abstract] |
Sunday, November 22, 2015 2:36PM - 2:49PM |
D38.00003: On linear instability of a flared cone at Ma 6 Xi Chen, Yiding Zhu, Cunbiao Lee LST calculations are performed on a flared cone over Mach 6 flow. The mean flow is efficiently obtained by first calculating the inviscid flow with FLUENT to get the flow information at the edge of the boundary layer, and then solving the nonsimilar boundary layer equations with spectral collocation method. The LST solver is based on spectral collocation method (global solver) and Malik's fourth-order compact finite-difference method (local solver). The profiles and frequency band of the second mode instability from LST are in nice agreement with experimental results obtaining by PIV and PCB. Three kinds of instabilities, i.e., steady and unsteady Gortler instability, first mode instability and second mode instability have been identified by a new criteria. The effect of the bulk viscosity on these instabilities is studied. At last, the inviscid linear stability analysis is performed to better understand the curvature effects on the stability. [Preview Abstract] |
Sunday, November 22, 2015 2:49PM - 3:02PM |
D38.00004: Wind tunnel experiments on two blunt cones at Ma6 Yunchi Zhang, Cunbiao Li Wind tunnel experiments are performed on two $5^\circ$ half-angle blunt cones over Mach 6 flow for $0^\circ$ and $10^\circ$ angle of attack. The temperature distributions on both windward and leeward sides are obtained by temperature sensitive painting (TSP) technique and the fluctuation pressure is measured by PCB pressure sensors for 7 meridian lines between the central meridian lines of the windward and the leeward by $30^\circ$ step. Boundary layer transition is implied by the temperature distribution and power spectral evolution of the fluctuation pressure. It is found there exists a streamwise high-temperature strip near the central meridian line of the leeward side and transition is most likely to occur along the strip (earlier than the windward side and $0^\circ$ angle of attack). Besides, the radius of the cone tip has an effective influence on the transition location. Transition is more likely to occur on the cone with the sharper tip. [Preview Abstract] |
Sunday, November 22, 2015 3:02PM - 3:15PM |
D38.00005: Bypass transition of the bottom boundary layer under solitary wave Mahmoud Sadek, Peter Diamessis, Luis Parras, Philip Liu The transition to turbulence in the bottom boundary layer (BBL) flow driven by a soliton-like pressure gradient in an oscillating water tunnel (an approximation for the BBL under solitary waves) is investigated using hydrodynamic linear stability theory and DNS. As observed in the laboratory experiment by Sumer et al. (2010), two possible transition scenarios exist. The first scenario is associated with the classical transition resulting from the breakdown of the exponentially growing 2-D Tollmien-Schlichting waves. The alternative scenario; i.e., bypass transition; takes place through formation of localized turbulent spots. The investigation of the latter transition scenario is performed in two steps. The first step consists of reformulating the linear stability analysis in the non-modal framework for the purpose of finding the optimum disturbance characteristics which lead to the formation of those turbulent spots. In the second step, the computed optimum noise structure is inserted in the 3D DNS in order to induce the formation of the turbulent spots and effectively simulate the bypass transition observed experimentally. [Preview Abstract] |
Sunday, November 22, 2015 3:15PM - 3:28PM |
D38.00006: Numerical simulations and linear stability analysis of a boundary layer developed on wavy surfaces Lorenzo Siconolfi, Simone Camarri, Jens H. M. Fransson The development of passive methods leading to a laminar to turbulent transition delay in a boundary layer (BL) is a topic of great interest both for applications and academic research. In literature it has been shown that a proper and stable spanwise velocity modulation can reduce the growth rate of Tollmien-Schlichting (TS) waves and delay transition. In this study, we investigate numerically the possibility of obtaining a stabilizing effect of the TS waves through the use of a spanwise sinusoidal modulation of a flat plate. This type of control has been already successfully investigated experimentally [1]. An extensive set of direct numerical simulations is carried out to study the evolution of a BL flow developed on wavy surfaces with different geometric characteristics, and the results will be presented here. Moreover, since this configuration is characterized by a slowly-varying flow field in streamwise direction, a local stability analysis is applied to define the neutral stability curves for the BL flow controlled by this type of wall modifications. These results give the possibility of investigating this control strategy and understanding the effect of the free parameters on the stabilization mechanism. [1]Fransson, Downs and Sattarzadeh. TSFP-9,Melbourne 05/30-06/03,2015 [Preview Abstract] |
Sunday, November 22, 2015 3:28PM - 3:41PM |
D38.00007: Effect of a 3D surface depression on boundary layer transition Hui Xu, Shahid Mughal, Spencer J. Sherwin The influence of a three-dimensional surface depression on the transitional boundary layer is investigated numerically. In the boundary layer transition, the primary mode is a Tollmien-Schlichting (TS) wave which is a viscous instability. These modes are receptive to surface roughness interacting with free stream disturbances and/or surface vibrations. In this paper, numerical calculations are carried out to investigate the effect of the depression on instability of the boundary layer. In order to implement linear analysis, two/three (2D/3D)-dimensional nonlinear Navier-Stokes equations are solved by spectral element method to generate base flows in a sufficient large domain. The linear analyses are done by the parabolic stability equations (PSE). Finally, a DNS calculation is done to simulate the boundary layer transition. [Preview Abstract] |
Sunday, November 22, 2015 3:41PM - 3:54PM |
D38.00008: Mixed mode transition in zero and adverse pressure gradient boundary layers Rikhi Bose, Paul Durbin Flow regimes exist where interaction of Klebanoff streaks and the Tollmien-Sclichting waves trigger transition but either mode is individually insufficient. Such interaction between orderly and bypass routes of transition is called Mixed mode transition. In zero pressure gradient boundary layers, mixed mode transition follows three routes depending upon strength of these perturbation modes. At high free-stream turbulence intensity ($Tu$), bypass transition is dominant and the flow is very weakly sensitive to the TS mode strength. In the presence of a strong TS mode, low $Tu$ triggers secondary instability of the TS wave forming $\Lambda$ vortices. The $\Lambda$ vortices are forced response due to the weak streaks rather than resonance mechanism seen in monochromatic excitations. When both of these modes are weak, secondary instability of streaks trigger consequent breakdown to turbulent spots. Three-dimensional visualization of the perturbation fields shows toroidal $n=0$ and helical $n=1$ modes observed in instability of axisymmetric jets and wakes. In adverese pressure gradient boundary layers, the presence of an inflection point significantly increases the growth rate of TS mode thereby strengthening the secondary instability route and the interaction is more interesting. [Preview Abstract] |
Sunday, November 22, 2015 3:54PM - 4:07PM |
D38.00009: Numerical modeling of the transitional boundary layer over a flat plate Dimitry Ivanov, Andrei Chorny Our example is connected with fundamental research on understanding how an initially laminar boundary layer becomes turbulent. We have chosen the flow over a flat plate as a prototype for boundary-layer flows around bodies. Special attention was paid to the near--wall region in order to capture all levels of the boundary layer. In this study, the numerical software package OpenFOAM has been used in order to solve the flow field. The results were used in a comparative study with data obtained from Large Eddy Simulation (LES). The composite SGS-wall model is presently incorporated into a computer code suitable for the LES of developing flat-plate boundary layers. Presently this model is extended to the LES of the zero--pressure gradient, flat-plate turbulent boundary layer. In current study the time discretization is based on a second order Crank-Nicolson/Adams-Bashforth method. LES solver using Smagorinsky and the one--equation LES turbulence models. The transition models significantly improve the prediction of the onset location compared to the fully turbulent models.LES methods appear to be the most promising new tool for the design and analysis of flow devices including transition regions of the turbulent flow. [Preview Abstract] |
Sunday, November 22, 2015 4:07PM - 4:20PM |
D38.00010: Transitional regime and laminar-turbulent coexistence in the asymptotic suction boundary layer Taras Khapko, Philipp Schlatter, Yohann Duguet, Dan Henningson We study numerically the asymptotic suction boundary layer (ASBL) in the transitional regime on the verge of laminarization. Starting from a turbulent state the Reynolds number $Re$ is decreased in small steps until the laminar state is established. This study protocol allows not only to investigate the regime at the onset of turbulence, but also to identify the critical Reynolds number $Re_g\approx270$, below which turbulence is not sustained. In other planar shear flows the transitional regime at the onset takes the form of stable laminar-turbulent bands, however in ASBL no regime of sustained laminar-turbulent coexistence has been identified. The flow stays fully turbulent even at the lowest $Re$ before laminarization. During the laminarization process streamwise turbulent and laminar avenues are created with no oblique interfaces between the two. This behavior is connected with the existence of a large-scale vertical transport, the feature that distinguishes ASBL from the other wall-bounded shear flows. After an artificial forcing is added canceling all spanwise and wall-normal fluctuations above $y^+=100$, transient oblique bands are observed similar to the ones in other subcritical shear flows, while the flow later laminarizes or becomes fully turbulent again. [Preview Abstract] |
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