Investigation of wakes generated by fractal plates in the compressible flow regime using large-eddy simulations

TL;DR

This study uses large-eddy simulations to analyze how fractal and square plates generate wakes in compressible flows, revealing differences in turbulence, wake behavior, and potential noise reduction at various Mach numbers.

Contribution

It introduces a detailed LES approach with an immersed boundary method to study fractal plate wakes in compressible flow, comparing them to square plates and validating with experimental data.

Findings

Fractal plates produce lower turbulent kinetic energy than square plates.

Wakes show increased lateral spread and meandering at higher Mach numbers.

Fractal plates may reduce aerodynamic noise based on pressure spectra analysis.

Abstract

We investigate flows interacting with a square and a fractal shape multi-scale structures in the compressible regime for Mach numbers at subsonic and supersonic upstream conditions using large-eddy-simulations (LES). We also aim at identifying similarities and differences that these interactions have with corresponding interactions in the canonical incompressible flow problem. To account for the geometrical complexity associated with the fractal structures, we apply an immersed boundary method to model the no-slip boundary condition at the solid surfaces, with adequate mesh resolution in the vicinity of the small fractal features. We validate the numerical results through extensive comparisons with experimental wind tunnel measurements at a low Mach number. Similar to the incompressible flow case results, we find a break-up of the flow structures by the fractal plate and an increase in turbulent mixing in the downstream direction. As the Mach number increases, we observe noticeable wake meandering and higher spread rate of the wake in the lateral direction perpendicular to the streamwise-spanwise plane. Although not significant, we quantify the difference between the square and the fractal plates using two-point velocity correlations across the Mach number range. The wakes generated by the fractal plate in the compressible regime showed lower turbulent kinetic energy (TKE) and energy spectra levels compared to those of the square case. Moreover, results in terms of the near-field pressure spectra seem to indicate that the fractal plate has the potential to reduce the aerodynamic noise.