Bulletin of the American Physical Society
76th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 19–21, 2023; Washington, DC
Session T26: Flow Instability: Boundary Layers and Transition II |
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Chair: Daniel israel, Los Alamos National Laboratory Room: 151A |
Monday, November 20, 2023 4:25PM - 4:38PM |
T26.00001: Linear stability of axisymmetric hypersonic flow over tangent-ogive cylinders Chandan Kumar, S Unnikrishnan, Datta V Gaitonde Insights into high-speed transition over canonical tangent-ogive forebodies (TOF) representative of hypersonic vehicles is obtained with a generalized formulation of the nonlinear spatial eigenvalue problem. The linear stability predictions identify amplification characteristics of first, second, and entropy-layer modes. Mode synchronization and phase-speed variations are quantified as a function of nose bluntness of the TOF. For sharp TOF, second mode instabilities dominate the growth rates, with progressively lower frequencies appearing further away from the leading edge, and exhibiting longer streamwise extents of amplification. The upper limit of the N-factor envelope is defined by lower-frequency second modes. Higher nose-bluntness attenuates the second modes, but gradients associated with strong shock curvature result in additional instability modes in the entropy layer. Complementary nonlinear simulations predict changes in transition mechanisms from secondary instabilities of roller-dominated second-mode structures in sharp TOF, to streak-dominated breakdown in blunter TOF, as in Klebanoff modes. |
Monday, November 20, 2023 4:38PM - 4:51PM |
T26.00002: Optimal perturbations in transitional Blasius boundary layers: A structured approach Aishwarya Rath, Chang Liu, Dennice F Gayme This work employs a structured input-output analysis (SIOA) (J. Fluid Mech. vol. 927, A25) approach to analyze the optimal perturbations in Blasius boundary layer flows. This approach incorporates the non-linear effects into input-output analysis that recovers the important flow features identified using non-linear analysis as demonstrated in canonical wall-bounded shear flows. For the Blasius boundary layer, the structured input-output response recovers the streamwise dependent structures that are most likely to trigger the transition consistent with direct numerical simulations. The associated flow structures most likely to be amplified (optimal perturbations) are identified based on structured uncertainty, which is decomposed into streamwise, wall-normal, and spanwise velocity correlations. The resulting optimal perturbations show that the streamwise velocity perturbations have the highest magnitude and wall-normal velocity perturbations have the smallest magnitude, which is consistent with non-linear optimal perturbations. |
Monday, November 20, 2023 4:51PM - 5:04PM |
T26.00003: On the characterization of the boundary-layer flow on a rotating slender cone using PIV Alberto F F Rius-Vidales, Ramis Örlü, Patricia Sujar-Garrido, Marios Kotsonis This work builds on previous investigations at KTH (e.g., Kato et al., 2019, PRF and Kato et al., 2021, JFM) on the development of boundary-layer instabilities and transition to turbulence on rotating cones in still fluid. There is still a limited understanding of the topology and evolution of instabilities in the slender cone case. Therefore, for this study, experiments were conducted on the setup (30-degree half-apex cone angle) presented by Kato et al (2021, JFM). The boundary-layer flow's topology and the instabilities that lead to transition are characterized using planar particle image velocimetry (PIV) for different rotational speeds. The time-average flow fields are compared to the corrected analytical solution proposed by Segalini and Camarri (2019, PRF) for rotating cones. In turn, the instantaneous velocity fields are analyzed in detail to characterize the topological evolution of the vortical structures presented in the classical flow visualizations by Kobayashi and Izumi (1983, JFM). In addition, the velocity measurements are supported by high-speed flow visualization. |
Monday, November 20, 2023 5:04PM - 5:17PM |
T26.00004: Effects of rainfall on laminal flow airfoils examined through the lens of turbulent spots and streaks Anthony M Settlemier, Saikishan Suryanarayanan Rainfall has been found to degrade airfoil performance through a variety of factors. This study focuses on one significant effect of raindrop impacts – the potential to cause early bypass transition within laminar flow near the leading edge. We examine this possibility through the lens of turbulent spots, wedges, and low-speed streaks, caused by static and transient disturbances in the boundary layer. Multiple impact scenarios are considered, including droplets rebounding from the airfoil, dispersing mass in the impact, and being absorbed into a water film. The complexity of each of these raindrop impact scenarios is abstracted as appropriate time-evolving body forces in our pseudo-spectral direct numerical simulations. The focus is interactions between a turbulent spot caused by the initial raindrop impact and the following disturbance, which may be a turbulent wedge, low-speed streak, or gradually evolve with time, depending on impact regime. The different scenarios are analyzed from both a local instability and vorticity dynamics points of view. Utilizing the results for improved modeling and potential mitigation of airfoil performance degradation due to rain or other transient phenomena will be discussed. |
Monday, November 20, 2023 5:17PM - 5:30PM |
T26.00005: Laminar-Turbulent Transition of Blasius Boundary-Layer Flows Using the Nonlinear One-Way Navier-Stokes (NOWNS) Approach Michael Sleeman, Matthew T Lakebrink, Tim Colonius The nonlinear One-Way Navier-Stokes (NOWNS) approach has recently been applied to perform stability analysis of two- and three-dimensional Blasius boundary layer flows. In NOWNS, a projection operator (based on the linearized Navier-Stokes equations) is applied to the nonlinear equations to remove upstream propagating modes, which results in a set of equations that can be solved efficiently in the frequency domain as a spatial initial-value problem. To date, the NOWNS approach has only been demonstrated for cases where the existing nonlinear parabolized stability equations (NPSE) are already effective. Therefore, we seek to demonstrate the advantages of the NOWNS approach by examining cases where the NPSE are less effective. In particular, we will consider boundary-layer flows with strong nonlinearities (where NPSE fails to converge), and cases with non-modal and multi-modal effects. We will validate against direct numerical simulation (DNS) results in the literature, and against an in-house harmonic balance method (HBM) code. |
Monday, November 20, 2023 5:30PM - 5:43PM |
T26.00006: Towards adaptive control of second mode instability in hypersonic boundary layer flow on a sharp circular base cone at zero angle of attack Kamil Dylewicz, Andres Goza, Vassilis Theofilis Modal and nonmodal linear instability analysis of hypersonic boundary layer flow on a sharp cone is performed, at conditions aligning with those of recent experiments in the BAM6QT facility. A 3deg half-angle circular base cone is placed at zero angle of attack against oncoming Mach 6 flow at unit Reynolds numbers 1.1E7 1/m < Re_1 < 1.2E7 1/m. Taylor-Macoll theory is used to compute post-shock conditions and provide edge conditions for the calculation of similar compressible boundary layer profiles. The temporal compressible axisymmetric linear stability eigenvalue problem is solved and N-factor computations reveal maximally amplified frequencies that fall well within one standard deviation of the experimental results. Subsequently, the initial value problem is solved and the short-time algebraic growth of perturbations is documented. Presently, development of a novel adaptive flow control strategy for modal and nonmodal boundary layer disturbances is underway, aiming at full coupling of reduced order model wall-dynamics and classic linear stability equations. Finally, a framework that incorporates the effect of surface motion, both prescribed and coupled to the flow dynamics via compliant metamaterials, on the resulting stability properties will be presented along with preliminary results. |
Monday, November 20, 2023 5:43PM - 5:56PM |
T26.00007: The role of large surface roughness in transition of 3D boundary layers Bo Yuan, Xuesong Wu Surface roughness can influence significantly transition of 3D boundary layers through alteration of the base flow whereby modifying crossflow stability or even inducing new instabilities. We study the impact of a wavy-wall roughness with a large height on the 3D boundary layer represented by the Falkner-Skan-Cooke flow. The flow structure is characterized by a wall layer, the main layer, and a critical layer. First, the immediate response to the roughness is in a viscous wall layer, where the disturbance is nonlinear. This layer converts the surface displacement into a 'blowing velocity' into the main layer. The nonlinear streaming effect in the wall layer leads to a mean flow distortion. In the main layer, which occupies the bulk of the boundary layer, the flow field is decomposed into the base flow, the steady streaming and the forced perturbations. The former is described by an initial-value problem, while the latter is governed by the Rayleigh equation, the solution to which becomes singular at a position denoted as the critical level. The singularity is resolved by introducing viscous effects in the critical layer. As the regularized solution acquires much greater amplitude, the critical layer is strongly nonlinear. There are velocity jumps coupling the dynamics in the critical layer and the main layer. Numerical solutions show that nonlinearity enhances the response. The secondary instability analysis indicates that the nonlinearly saturated critical layer can support strong inviscid instability. |
Monday, November 20, 2023 5:56PM - 6:09PM |
T26.00008: Toward data-driven transient growth analysis Zhicheng Kai, Peter K Frame, Aaron S Towne Non-modal stability analysis plays a crucial role in understanding bypass transition by identifying transient growth arising from the linearized Navier-Stokes operator. Typically, these analyses require access to temporal or spatial propagation operators that are not always easily obtained, especially for multi-physics problems. In this study, we propose an exclusively data-driven approach for transient growth analysis. Our method is derived by solving an optimization problem for the most amplified input and output modes that lie within the span of the data and can alternatively be understood in terms of a variant of dynamic mode decomposition. To validate our approach, we apply it to the complex Ginzburg-Landau equation and assess its robustness to measurement and process noise within the data. Finally, we demonstrate its practical utility by using it to study spatial transient growth in a transitional boundary layer. |
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