Unsteady pressure distributions on a 4:1 rectangular cylinder: comparison of numerical and experimental results using decomposition methods.

Detached flows around bluff bodies are ubiquitous in civil engineering applications.
In this work, the flow around a static 4:1 rectangular cylinder at moderate Reynolds number and at different angles of incidence is studied using both Experimental Fluid Dynamics (EFD) and Computational Fluid Dynamics (CFD).
Typically, the integration of EFD and CFD allows a better understanding of the flow of interest by leveraging the complementary of their respective outputs.
However, the comparison of computational and experimental results is an important but difficult step of this integration, particularly in the case of local quantities related to unsteady flows.
In this work, decomposition methods are used to compare unsteady loads and pressure distributions coming from EFD and CFD.
In particular, Proper Orthogonal Decomposition (POD) and Dynamic Mode Decomposition (DMD) are used to extract the dominant structures of the aerodynamic coefficients.
The experimental data are obtained from dynamic pressure measurements in wind tunnel while numerical data come from two-dimensional unsteady Reynolds-Averaged Navier-Stokes (uRANS) simulations and tri-dimensional Delayed-Detached Eddy Simulations (DDES).
This work shows that the decomposition methods represent a powerful tool enabling the analysis and the quantitative comparison of the main spatial and temporal characteristics of unsteady flows.
Moreover, the accuracy of uRANS and DDES results is analyzed in light of the capacity of both CFD techniques to capture the reattachment occurring on the upper part of the rectangular cylinder.