Abstract The unstable dynamics of a transitional laminar separation bubble behind two-dimensional bump geometry is investigated experimentally using dye visualizations and particle image velocimetry measurements. For Reynolds numbers above critical value, the initially recirculation subject to modulations in spanwise direction which can trigger vortex shedding. Increasing number further, behaviour dominated by low-frequency flapping motion, well known transonic flows, here for first time an...

The linear instability mechanisms of horizontal convection in a rectangular cavity forced by buoyancy gradient along its surface are investigated using local and global stability analyses for Prandtl number equal to unity. results show that the base flow, steady circulation characterized narrow descending plume broad upwelling region, depends on Rayleigh number, $Ra$ . For free-slip boundary conditions at critical value $Ra\approx 2\times 10^{7}$ , flow becomes unstable three-dimensional...

Abstract The wake of a sphere rolling along wall at low Reynolds number is investigated numerically and experimentally. Two successive transitions are identified in this flow, as the increased. first leads to periodic shedding planar symmetric hairpin vortices. second previously unknown transition involves loss symmetry low-frequency lateral oscillation wake, exhibiting surprising 7:3 resonance with vortex shedding. two characterized by dye visualizations quantitative information obtained...

In the present work, an optimization methodology to compute best control parameters, χ and Δ, for selective frequency damping method is presented. The does not suppose any a priori knowledge of flow physics, neither underlying numerical methods, especially suited simulations requiring large quantity grid elements processors. It allows obtaining optimal convergence rate steady state damped Navier-Stokes system. This achieved using Dynamic Mode Decomposition, which snapshot-based method,...

The stability and sensitivity of two- three-dimensional global modes developing on steady spanwise-homogeneous laminar separated flows around NACA 4412 swept wings are numerically investigated for different Reynolds numbers ${\textit {Re}}$ angles attack $\alpha$ . wake dynamics is driven by the two-dimensional von Kármán mode whose emergence threshold in $\alpha \unicode{x2013}{\textit plane computed with that centrifugal mode. At critical number, Strouhal streamwise wavenumber spanwise...

Horizontal convection at large Rayleigh and Prandtl numbers is studied experimentally in a regime up to seven orders of magnitude larger terms than previously achieved. To reach $10^{17}$ , the horizontal density gradient generated using differential solutal by input salt fresh water controlled diffusion novel experiment which zero-net mass flux ensured through permeable membranes. This set-up allows us accurately measure Nusselt number carefully controlling amount exchanged Combined...

Abstract The structure of a stratified boundary layer over tilted bottom with small streamwise undulation is studied theoretically and numerically. We show that the tilt can induce strong density variations wall-transverse velocities in critical when frequency forcing by topography $\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq \ge =\geqslant \geq \def \Pr {\mathit {Pr}}\def \Fr {Fr}}\def \Rey {Re}}kU(z_c)$ equal to transverse Brunt–Väisälä $N...

We report an extensive experimental investigation into the effects of inflow turbulence on a simplified road vehicle, so-called square back Ahmed body. Variations reaching up to +16% and −17% drag coefficient are observed for free-stream representative open-road conditions [J. W. Saunders R. B. Mansour, “On-road wind tunnel its measurement using four-hole dynamic probe ahead several cars,” SAE Trans. 109, 477 (2000)]. Regular grids mounted upstream The intensity integral length scale varied...

This paper is associated with a poster winner of 2016 APS/DFD Milton van Dyke Award for work presented at the DFD Gallery Fluid Motion. The original available from Motion, https://doi.org/10.1103/APS.DFD.2016.GFM.P0028

The performances of two multivariate interpolation procedures are compared using functions that either synthetic or coming from a shape optimization problem in aerodynamics. aim is to evaluate the efficiency adaptive sparse algorithms 2 and compare them with kriging approach developed for design analysis computer experiment (DACE) 21. accuracy computational time methods examined as number N samples used increases. It appears our test cases both perform equivalently, terms precision. However,...

Machine learning control is applied in real-time to an airfoil equipped with variable-velocity jets and pressure sensors a closed-loop wind tunnel. The objective of the improve lift-to-drag ratio using array variable velocity located at leading edge wing model. Pressure are along chord, mid-span, used feedback strategy where symbolic laws optimized linear genetic programming (LGPC) algorithm. For angles attack onset stall, we show that best law able outperform open-loop case single-input...

The dynamics of perturbations to large-amplitude internal solitary waves (ISWs) in two-layered flows with thin interfaces is analysed by means linear optimal transient growth methods. Optimal are computed through direct–adjoint iterations the Navier–Stokes equations linearized around inviscid, steady ISWs obtained from Dubreil-Jacotin–Long (DJL) equation. found as a function ISW phase velocity $c$ (alternatively amplitude) for one representative stratification. These disturbances be...