On the relationship between the base pressure and the velocity in the near-wake of an Ahmed body

TL;DR

This study explores the link between base pressure and near-wake velocity in an Ahmed body, revealing how large-scale flow structures relate to pressure fluctuations and wake dynamics through numerical simulations and modal analysis.

Contribution

It demonstrates the relationship between base pressure modes and near-wake velocity fields, using POD and stochastic estimation techniques, providing new insights into wake-flow interactions.

Findings

Switches between asymmetric wake states are characterized by antisymmetric POD modes.

Large-scale symmetric modes are responsible for base suction reduction.

Near-wake velocity fields can be partially reconstructed from base pressure modes.

Abstract

We investigate the near-wake flow of an Ahmed body which is characterized by switches between two asymmetric states that are mirrors of each other in the spanwise direction. The work focuses on the relationship between the base pressure distribution and the near-wake velocity field. Using direct numerical simulation obtained at a Reynolds number of 10000 based on incoming velocity and body height as well as Bonnavion and Cadot's experiment (Bonnavion et al. 2018), we perform Proper Orthogonal Decomposition (POD) of the base pressure field. The signature of the switches is given by the amplitude of the most energetic, antisymmetric POD mode. However switches are also characterized by a global base suction decrease, as well as deformations in both vertical and lateral directions, which all correspond to large-scale symmetric modes. Most of the base suction reduction is due to the two most energetic symmetric modes. Using the linear stochastic estimation technique of Podvin et al. 2018, we show that the large scales of the near-wake velocity field can be recovered to some extent from the base pressure modes. Conversely, it is found that the dominant pressure modes and the base suction fluctuation can be well estimated from the POD velocity modes of the near-wake.