Flow coherent structures and frequency signature: Application of the dynamic modes decomposition to open cavity flow

International audienceThe dynamic dimension of an impinging flow may be significantly reduced by its boundary conditions and self-sustained oscillations they induce. The spectral signature is associated with remarkable spatial coherent structures. Dynamic modes decomposition (DMD) makes it possible to directly extract the dynamical properties of a non-linearly saturated flow. We apply DMD to highlight the spectral contribution of the longitudinal and transverse structures of an experimental open-cavity flow

Spectral/hp element simulation of flow past a Formula One front wing: validation against experiments

Emerging commercial and academic tools are regularly being applied to the design of road and race cars, but there currently are no well-established benchmark cases to study the aerodynamics of race car wings in ground effect. In this paper we propose a new test case, with a relatively complex geometry, supported by the availability of CAD model and experimental results. We refer to the test case as the Imperial Front Wing, originally based on the front wing and endplate design of the McLaren 17D race car. A comparison of different resolutions of a high fidelity spectral/hp element simulation using under-resolved DNS/implicit LES approach with fourth and fifth polynomial order is presented. The results demonstrate good correlation to both the wall-bounded streaklines obtained by oil flow visualization and experimental PIV results, correctly predicting key characteristics of the time-averaged flow structures, namely intensity, contours and locations. This study highlights the resolution requirements in capturing salient flow features arising from this type of challenging geometry, providing an interesting test case for both traditional and emerging high-fidelity simulations

The atmospheric boundary layer over urban-like terrain: influence of the plan density on roughness sublayer dynamics

We investigate the effect of the packing density of cubical roughness elements on the characteristics of both the roughness sublayer and the overlying turbulent boundary layer, in the context of atmospheric flow over urban areas. This is based on detailed wind-tunnel hot-wire measurements of the streamwise velocity component with three wall-roughness configurations and two freestream flow speeds. The packing densities are chosen so as to obtain the three near-wall flow regimes observed in urban canopy flows, namely isolated-wake, wake-interference and skimming-flow regimes. Investigation of the wall-normal profiles of the one-point statistics up to third order demonstrates the impossibility of finding a unique set of parameters enabling the collapse of all configurations, except for the mean streamwise velocity component. However, spectral analysis of the streamwise velocity component provides insightful information. Using the temporal frequency corresponding to the peak in the pre-multiplied energy spectrum as an indicator of the most energetic flow structures at each wall-normal location, it is shown that three main regions exist, in which different scaling applies. Finally, scale decomposition reveals that the flow in the roughness sublayer results from a large-scale intrinsic component of the boundary layer combined with canopy-induced dynamics. Their relative importance plays a key role in the energy distribution and influences the near-canopy flow regime and its dynamics, therefore suggesting complex interactions between the near-wall scales and those from the overlying boundary layer

Dynamic/Koopman modes of an experimental incompressible cavity flow

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Wind Profiler Related Research in the Tropical Pacific

ABSTRACf This paper is broadly concerned with the application of wind profiling Doppler radar technology to tropical atmospheric research. Examples of the use of wind profilers in the tropics are drawn from the Aeronomy Laboratory's wind profilers located on Pohnpei (7"N, 158'E) and Christmas Island (2°N, 157·W). The Pohnpei wind profiler was constructed in 1984 and has been used exclusively to observe vertical motions. The Christmas Island wind profiler has observed horizontal and vertical velocities routinely since 1986. These two wind profilers form part of a planned trans-Pacific network of wind-profiling radars that will eventually span the tropical Pacific

Flow dynamics in the roughness sublayer of atmospheric boundary layers

The present work investigates the influence of the packing density (λ p ) of a cube-based canopy on the interaction between the most energetic structures of both the logarithmic layer and the roughness sublayer of an atmospheric boundary layer. Analysis of one- and two-point hot-wire anemometry measurements shows that increasing λ p leads to a change in the near-canopy flow regime for which the coherent structures from the outer layer dominate