Work Description

Turbulent flow over a backward-facing ramp with wall-mounted cubes [Data set]

== Dataset Information ==

Date : May 24, 2023
Creator : S. Tandon, K. J. Maki, E. Johnsen
Contact : suyashtn@umich.edu
Funding : This work used the Extreme Science and Engineering Discovery Environment’s (Towns et al. (2014)) Stampede2 system at the Texas Advanced Computing Center (TACC), which is supported by the National Science Foundation grant number ASC-160041.
Software: OpenFOAM® version 4.0 or newer

== Key Points ==

A few important highlights of the dataset are:
* Wall-resolved large eddy simulations (LES) is used to investigate turbulent flow over a backward-facing ramp with wall-mounted cubes.
* High-fidelity 3-D flow is computed to study the interaction between the turbulent structures near the cube (vortex generator) and the separated region.
* Dependence of turbulent structure and kinetic energy budget on the cube configuration (height and position) is studied.

== Summary ==

The separation of spatially evolving turbulent boundary layer flow near regions of adverse pressure gradients has been the subject of numerous studies. Although many studies have demonstrated the efficacy of passive flow control devices, such as vortex generators (VGs), in the separated region, the interactions between the salient flow structures produced by VGs and those of the separated flow are not fully understood. In this study, a spatially evolving turbulent boundary layer interacting with wall-mounted cubes ahead of a backward-facing ramp (BFR) is investigated using wall-resolved large-eddy simulations (LES) for a Reynolds number of 19,600 (based on the inlet boundary layer thickness δ0 and freestream velocity). The horseshoe vortex system observed around a cube entrains the freestream turbulent flow towards the plane of symmetry. These localized regions of high vorticity correspond to turbulent kinetic energy production regions, which effectively transfer energy from the freestream to the near-wall regions. While significantly lower levels of dissipation of turbulent kinetic energy than the production are observed in the outer flow regions of the horseshoe vortex and the induced counter-rotating flow, the spatial distribution of dissipation is similar to that of the turbulent kinetic energy. Two flow configurations with a single cube are examined to isolate and study the effects of cube height and streamwise position of the cube.

== Methodology ==

The data are output from LES conducted with open source CFD solver OpenFOAM®

== Dataset Contents ==

Two compressed .zip files are provided which contain different flow configurations considered for simulations and analysis of flow field. The folders and simulations are described below:
* no vg: BFR with no cube. The undisturbed spatially evolving turbulent boundary layer is simulated over the expansion section for approximately 100 flow overs, and dynamics of the separated flow over the ramp is analyzed
* single vg: BFR with a single wall-mounted cube. Three cube heights h/delta_0 = 0.2, 0.6 and 1 with fixed xvg = 3h and three cube positions xvg/h = 0,3 and 6 with fixed h/delta_0 = 0.6 are considered and dependence of turbulent transport on these parameters is investigated. The h/delta_0 = 0.6 with xvg/h = 3 is considered as baseline, and a total of 5 configurations are simulated for 100 flow overs each.

Structure of a test case:

├── 0
│   ├── U
│   ├── p
│   └── ...
├── 100
│   ├── U
│   ├── UMean
│   ├── UPrime2Mean
│   └── ...
├── constant
│   ├── polyMesh
│   ├── transportProperties
│   └── ...
├── system
│   ├── controlDict
│   ├── fvSolution
│   └── ...

1. 0: Contains the initial condition configuration for the flow fields—velocity (U), pressure (p), kinematic viscosity (nut) and modeled turbulent kinetic energy (k).
2. 100: Contains the 3D field values of velocity fields U and UMean, Reynolds stress tensor UPrime2Mean and pressure p. These field values are recorded after running the simulation for 100+ flow overs through the expansion section and quantities are time-averaged.
3. constant: The mesh files are held in this sub-directory. OpenFOAM® employs unstructured mesh, and specifications of neighbor, owner, faces, cell indices and point labels are recorded in separate files.
3.1 polyMesh: contains the description of the unstructured mesh
3.2 turbulenceProperties: provides specifications of turbulence models used
3.2 transportProperties: provides description of flow transport properties
4. system: Configuration and tuning parameters to specify the scheme selection and control simulation run-time are provided in different dictionary files.
4.1 controlDict: a dictionary to control the start time, end time, and other functionality of the simulations
4.2 fvSolution: a dictionary to provide options for solvers, preconditioners and smoothers
4.3 fvSchemes: a dictionary to specify the schemes for gradient calculations, time derivatives, interpolation, etc.

** NOTE **
With these four sub-directories provided for each of the 6 flow configurations, including both no vg and single vg, ideally one can use:
* OpenFOAM® (https://openfoam.org/ or https://www.openfoam.com/) utilities such as postProcess to evaluate other quantities of interest, like Q-criterion, vorticity, turbulent kinetic energy, etc.
* ParaView (https://www.paraview.org) to visualize the 3D dataset.
* Custom scripts that can help extract field quantities are available in this repository (https://github.com/suyashtn/scripts)
Use and access: This data set is made available under a Creative Commons Public Domain license (CC 4.0).

== Citation ==

To cite data: Tandon, S., Johnsen, E. and Maki, K. (2023). Turbulent flow over a backward-facing ramp
with wall-mounted cubes [Data set], University of Michigan - Deep Blue Data.