Analysis of improved digital filter inflow generation methods for compressible turbulent boundary layers

Luis Laguarda, Stefan Hickel*

*Corresponding author for this work

Research output: Contribution to journalArticleScientificpeer-review

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Abstract

We propose several enhancements to improve the accuracy and performance of the digital filter turbulent inflow generation technique and assess their efficacy in the context of wall-resolved large-eddy simulations of a compressible turbulent boundary layer. Improvements of accuracy include a more realistic correlation function for the transversal directions, target length scales that vary with wall-distance, and a counter-intuitive approach that involves the suppression of streamwise velocity fluctuations at the inflow. For improving the computational performance, we propose to generate the inflow data in parallel in single precision and at a prescribed time interval based on the turbulence time scale, and not at every time-step of the simulation. Based on the results of 7 wall-resolved large-eddy simulations, we find that the new correlation functions and the considered performance improvements are beneficial and therefore desired. Suppressing streamwise velocity fluctuations at the inflow leads to the fastest relaxation of the pressure fluctuations; however, this approach increases the adaptation length defined in terms of compliance with the von Kármán integral equation. The adaptation length can be shortened by artificially increasing the wall-normal Reynolds stresses, thereby preserving the desired turbulence kinetic energy level. A detailed inspection of the Reynolds stress transport budgets reveals that the observed spurious spatial transients are largely driven by pressure-related terms. For instance, increased values of up¯ are found throughout the computational domain when a physical Reynolds stress distribution is prescribed at the inflow. Therefore, efforts to enhance digital filter techniques should aim at modeling pressure fluctuations as well as their correlation with the velocity components.

Original languageEnglish
Article number106105
Number of pages9
JournalComputers and Fluids
Volume268
DOIs
Publication statusPublished - 2024

Funding

We acknowledge PRACE for awarding us access to HAWK at the High-Performance Computing Center Stuttgart, Germany.

Keywords

  • Digital filter
  • Turbulence resolving simulation
  • Turbulent inflow generation

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