1,720,976 research outputs found
Shock-wave/boundary-layer interactions with sidewall effects in the OpenSBLI code-generation framework
No full textNumerical work on shockwave/boundary-layer interactions (SBLIs) to date has largely focused on span-periodic quasi-2D configurations that neglect the influence lateral confinement has on the core flow. The present thesis is concerned with the effect of flow confinement on Mach 2 laminar and transitional SBLI in rectangular ducts. An oblique shock generated by a deflection plate forms a conical swept SBLI with sidewall boundary layers before reflecting from the bottom wall of the domain. In the laminar cases, multiple large regions of flow-reversal are observed on the sidewalls, bottom wall and at the corner intersection of the duct. The main interaction is found to be strongly three-dimensional and highly dependent on the geometry of the duct. Comparison to quasi-2D span-periodic simulations showed that sidewalls strengthen the main interaction, with a 31% increase in the central separation bubble length for the baseline aspect ratio one configuration. Parametric studies of shock strength and duct aspect ratio were performed to find limiting behaviours. Topological features of the three-dimensional separation are identified and shown to be consistent with ‘owl-like’ separations of the first kind.Time-dependent forcing strips are added to the laminar duct to generate disturbances for the transitional SBLI cases. The transition is observed to develop first in the low-momentum corners of the duct and spread out in a wedge shape. The central separation bubble is seen to react dynamically to oncoming turbulent spots, shifting laterally across the span. While instantaneous corner separations do occur, the time-averaged corner flow remains attached. An assessment of low-dissipative shock-capturing schemes is also performed for transitional and turbulent shock interactions. Targeted Essentially Non-Oscillatory (TENO) schemes are found to provide improved resolution for compressible turbulence compared to conventional Weighted Essentially Non-Oscillatory (WENO) schemes.A significant portion of the PhD project has involved the co-development of a new open-source CFD code named OpenSBLI. OpenSBLI is a Python-based code-generation framework that generates C code in the Oxford Parallel Structured (OPS) embedded Domain Specific Language (eDSL). OpenSBLI is an explicit CFD solver for the 3D compressible Navier-Stokes equations, utilizing high-order finite-difference schemes on structured meshes. The simulation code generated by OpenSBLI targets massively-parallel High-Performance Computing (HPC) architectures including CPUs, GPUs and many-core accelerator cards. The thesis documents the structure and implementation of the code. A suite of validation cases are performed to demonstrate the accuracy and correctness of the code implementation
Assessment of low dissipative shock capturing schemes for the compressible Taylor Green vortex
No full textInteractions between shock-waves and turbulence are ubiquitous in high-speed flows of practical aeronautical interest. Recent advances in computational power have made Implicit Large Eddy Simulation (ILES) and Direct Numerical Simulation (DNS) feasible tools for investigating the underlying physical mechanisms involved. However, numerical methods for shock-capturing introduce high levels of numerical dissipation to the whole flow-field, making them a poor choice for resolving the small scales of turbulence. In this work the efficacy of a selection of low-dissipative and hybrid Weighted and Targeted Essentially Non-Oscillatory (WENO/TENO) shock-capturing methods is assessed. An extension of the classic subsonic Taylor-Green vortex problem is presented up to Mach 1.25, where compressibility and dilatational dissipation become important. The presence of strong shock-waves is demonstrated, which merge and interact with one another to form complex shock systems. A supersonic test case is then specified, using a Reynolds number of 1600 to ensure a wide range of scales are present to test the numerical schemes. Low-dissipative TENO schemes are found to offer substantial improvements in resolution over established WENO methods for a comparable computational cost
The effect of flow confinement on laminar shock-wave/boundary-layer interactions
No full textNumerical work on shock-wave/boundary-layer interactions (SBLI) to date has largely focused on span-periodic quasi-two-dimensional (quasi-2-D) configurations that neglect the influence lateral confinement has on the core flow. The present study is concerned with the effect of flow confinement on Mach 2 laminar SBLI in rectangular ducts. An oblique shock generated by a wedge forms a conical swept SBLI with sidewall boundary layers before reflecting from the bottom wall of the domain. Multiple large regions of flow-reversal are observed on the sidewalls, bottom wall and at the corner intersection. The main interaction is found to be strongly three-dimensional and highly dependent on the geometry of the duct. Comparison to quasi-2-D span-periodic simulations showed sidewalls strengthen the interaction by 31 % for the baseline configuration with an aspect ratio of one. The length of the shock generator and subsequent trailing edge expansion fan position was shown to be a critical parameter in determining the central separation length. By shortening the length of the shock generator, modification of the interaction and suppression of the central interaction is demonstrated. Parametric studies of shock strength and duct aspect ratio were performed to find limiting behaviours. For the largest aspect ratio of four, three-dimensionality was visible across 30 % of the span width away from the wall. The topology of the three-dimensional separation is shown to be similar to 'owl-like' separations of the first kind. Reflection of the initial conical swept SBLI is found to be the most significant factor determining the flow structures downstream of the main interaction.</p
Dataset: Shock-wave/boundary-layer interactions with sidewall effects in the OpenSBLI code-generation framework
Full text linkDataset to accompany the PhD thesis of the same name. [1] D.J Lusher. Shock-wave/boundary-layer interactions with sidewall effects in the OpenSBLI code-generation framework.
The PhD project was funded by an EPSRC Centre for Doctoral Training grant (EP/L015382/1). Compute resources used in this work were provided by the `Cambridge Service for Data Driven Discovery' (CSD3) system operated by the University of Cambridge Research Computing Service (http://www.hpc.cam.ac.uk) funded by EPSRC Tier-2 capital grant EP/P020259/1, and the IRIDIS5 High Performance Computing Facility, and associated support services at the University of Southampton.</span
2D Laminar shock-wave/boundary-layer interaction in OpenSBLI
No full textThis dataset contains the result of the Mach 2 2D laminar shock-wave/boundary-layer interaction validation case, performed in the automatic source code generation framework OpenSBLI.
The corresponding paper is:
Lusher, D. J., Jammy, S. P., & Sandham, N. D. (2018). Shock-wave/boundary-layer interactions in the automatic source-code generation framework OpenSBLI. Computers and Fluids, 1-5. DOI:10.1016/j.compfluid.2018.03.081</span
Shock-wave/boundary-layer interactions in transitional rectangular duct flows
No full textShock-wave/boundary-layer interactions (SBLI) are an important feature of high-speed gas dynamics. In many numerical studies of SBLI span-periodicity is assumed to reduce computational complexity. However, span-periodicity is not a valid assumption for aeronautical applications such as supersonic engine intakes where lateral confinement leads to highly three-dimensional behaviour. In this work transitional oblique SBLI are simulated for a rectangular duct with θsg = 5º shock generator ramp at Mach 2. The baseline configuration is a duct with an aspect ratio of 0.5. Time-dependent disturbances are added to the base laminar flow via wall localised blowing/suction strips to obtain intermittent transition upstream of the SBLI. Two forcing configurations are evaluated to assess the response of the SBLI to different tripping locations. The transition is observed to develop first in the low-momentum corners of the duct and spread out in a wedge shape. The central separation bubble is seen to react dynamically to oncoming turbulent spots, shifting laterally across the span. While instantaneous corner separations do occur, the time-averaged corner flow remains attached. Comparisons to a one-to-one aspect ratio duct show that the SBLI is heavily dependent on aspect ratio; the wider duct exhibited significantly larger regions of flow-reversal due to a strengthened interaction
OpenSBLI: automated code-generation for heterogeneous computing architectures applied to compressible fluid dynamics on structured grids
No full textOpenSBLI is an open-source code-generation system for compressible fluid dynamics (CFD) on heterogeneous computing architectures. Written in Python, OpenSBLI is an explicit high-order finite-difference solver on structured curvilinear meshes. Shock-capturing is performed by a choice of high-order Weighted Essentially Non-Oscillatory (WENO) or Targeted Essentially Non-Oscillatory (TENO) schemes. OpenSBLI generates a complete CFD solver in the Oxford Parallel Structured (OPS) domain specific language. The OPS library is embedded in C code, enabling massively-parallel execution of the code on a variety of high-performance computing architectures, including GPUs. The present paper presents a code base that has been completely rewritten from the earlier proof of concept (Jacobs et al, JoCS 18 (2017), 12-23), allowing shock capturing, coordinate transformations for complex geometries, and a wide range of boundary conditions, including solid walls with and without heat transfer. A suite of validation and verification cases are presented, plus demonstration of a large-scale Direct Numerical Simulation (DNS) of a transitional Shockwave Boundary Layer Interaction (SBLI). The code is shown to have good weak and strong scaling on multi-GPU clusters. We demonstrate that code-generation and domain specific languages are suitable for performing efficient large-scale simulations of complex fluid flows on emerging computing architectures
Direct numerical simulations and spectral proper orthogonal decomposition analysis of shocklet-containing turbulent channel counter-flows
No full textCounter-flow configurations in a confined channel flow provide an efficient framework to study high intensity turbulent mixing processes. In a previous study (Physical Review Fluids, 6(9), p.094603), a wall-bounded counter-flow turbulent channel configuration was presented as an effective framework for addressing certain challenges related to the study of compressibility effects on turbulence as an alternative to free shear layer and Poiseuille/Couette type flows. Here, the previous direct numerical simulations are extended to a higher Mach number (M=0.7) to quantify direct and indirect effects of compressibility. It is found that the configuration is able to produce large numbers of embedded shocklets, leading to significant asymmetry in probability density functions of dilatation. Reducing the Prandtl number from 0.7 to 0.2 increases the compressibility effect further by reducing the bulk heating in the channel. A peak turbulent Mach number close to unity is obtained, for which the contribution of the dilatational dissipation to the total dissipation is nevertheless found to be limited to ∼6%. Indirect effects of compressibility are much larger, with changes of up to 40% in Favre normal stresses, despite the mean flow and shear stress being almost unaffected by compressibility in this configuration. Given the inflectional nature of the turbulent mean flow it is also interesting to identify large structures. Spectral Proper Orthogonal Decomposition (SPOD) reveals a full spectrum with a slow decay of energy with mode number. Mode shapes are three-dimensional with the low frequencies displaying elongated streaks in the velocity field at the channel centre plane.</p
DNS of a counter-flow channel configuration
No full textMean flow and turbulence statistics of a compressible turbulent counter-flow channel configuration. This dataset is based on direct numerical simulations conducted using OpenSBLI (https://opensbli.github.io/), a Python-based automatic source code generation and parallel computing framework for finite difference discretisation. #============================================================================================== # Please cite the following paper when publishing using this dataset: # Title: Direct numerical simulation of compressible turbulence in a counter-flow channel configuration # Authors: Arash Hamzehloo, David Lusher, Sylvain Laizet and Neil Sandham # Journal: Physical Review Fluids # DOI: https://doi.org/10.1103/PhysRevFluids.6.094603 # ============================================================================================== Please note: Tables 1 and 2 of the above paper provide more detailed information on the counter-flow channels of this dataset. Each folder name of this dataset includes the Mach number, Reynolds number, domain size and grid resolution of a particular case, respectively. In each file, the first column contains the grid-point coordinates in the wall-normal direction () with the channel centreline located at . The mean stresses are defined as . Angle brackets denote averages over the homogeneous spatial directions (streamwise and spanwise ) and time. The Favre average is related to the Reynolds average as . The mean Mach number is defined as where is the local speed of sound. The turbulent Mach number is defined as . # ============================================================================================== Details of the OpenSBLI framework, its numerical methodology and existing flow configurations can be found in the following papers: OpenSBLI: Automated code-generation for heterogeneous computing architectures applied to compressible fluid dynamics on structured grids. (link) OpenSBLI: A framework for the automated derivation and parallel execution of finite difference solvers on a range of computer architectures. (link) On the performance of WENO/TENO schemes to resolve turbulence in DNS/LES of high‐speed compressible flows. (link)</span
Shock-wave/boundary-layer interactions in the automatic source-code generation framework OpenSBLI
No full textLaminar shock-wave/boundary-layer interactions were simulated using OpenSBLI, a Python-based source code generation framework. Shock-capturing was performed by a 5th order finite-difference Weighted Essentially Non-Oscillatory (WENO)-Z scheme applied in characteristic space. Oblique shock conditions were imposed for a shock angle of θ=32.58∘ and Mach 2 free-stream, impinging on a laminar flat-plate boundary-layer. Performance of the code was assessed on different architectures for CPU, GPU and Xeon Phi.</p
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