1,721,134 research outputs found
Dataset for Surface correlations of hydrodynamic drag for transitionally rough engineering surfaces
No full textDetails of the content of the dataset can be found in the readme.txt file.
Dataset supporting:
Thakkar, Manan, Busse, Angela and Sandham, Neil (2016) Surface correlations of hydrodynamic drag for transitionally rough engineering surfaces. Journal of Turbulence.</span
Dataset for 'Turbulence structures and statistics of a supersonic turbulent boundary layer subjected to concave surface curvature'
No full textThis dataset contains data files for the paper
"Turbulence structures and statistics of a supersonic turbulent boundary layer subjected to concave surface curvature" by Sun, Mingbo; Sandham, Neil; Hu, Zhiwei published by Journal of Fluid Mechanics.
They can be opened in Tecplot</span
Enstrophy and kinetic energy data from 3D Taylor-Green vortex simulations
No full textEnstrophy and kinetic energy data from four 3D Taylor-Green vortex simulations, using uniform grids of 64^3, 128^3, 256^3, and 512^3 solution points. The simulations were performed using the OpenSBLI code developed at the University of Southampton.
Dataset to support:
Jammy, Satya, Jacobs, Christian and Sandham, Neil (2016) Performance evaluation of explicit finite difference algorithms with varying amounts of computational and memory intensity. Journal of Computational Science, 1-15.</span
Effects of compressibility and shock-wave interactions on turbulent shear flows
No full textCompressibility effects are present in many practical turbulent flows, ranging from shockwave/boundary-layer interactions on the wings of aircraft operating in the transonic flight regime to supersonic and hypersonic engine intake flows. Besides shock wave interactions,compressible flows have additional dilatational effects and, due to the finite sound speed, pressure fluctuations are localized and modified relative to incompressible turbulent flows. Such changes can be highly significant, for example the growth rates of mixing layers and turbulent spots are reduced by factors of more than three at high Mach number. The present contribution contains a combination of review and original material. We first review some of the basic effects of compressibility on canonical turbulent flows and attempt to rationalise the differing effects of Mach number in different flows using a flow instability concept. We then turn our attention to shock-wave/boundary-layer interactions, reviewing recent progress for cases wherestrong interactions lead to separated flow zones and where a simplified spanwise-homogeneous problem is amenable to numerical simulation. This has led to improved understanding, in particular of the origin of low-frequency behaviour of the shock wave and shown how this is coupled to the separation bubble. Finally, we consider a class of problems including side walls that is becoming amenable to simulation. Direct effects of shock waves, due to their penetration into the outer part of the boundary layer, are observed, as well as indirect effects due to the high convective Mach number of the shock-induced separation zone. It is noted in particular how shock-induced turning of the detached shear layer results in strong localized damping of turbulence kinetic energy
Incipient buffet over laminar-flow airfoil - a DNS study at moderate Reynolds numbers
No full textIn order to study transonic buffet over aircraft wings, the linear stability of the flowfield is analysed based on direct numerical simulations at moderate Reynolds numbers. A significant change of the boundary layer stability depending on the aerodynamic load of the airfoil is suggested by local linear stability theory. Besides Kelvin Helmholtz instabilities, a global mode, showing the coupled dynamics of the separation bubbles, can be identified in agreement with literature. Both modes are present in a dynamic mode decomposition (DMD) of the unsteady direct numerical solution. Furthermore, DMD picks up the buffet-mode at a Strouhal number of St = 0.12 that agrees with experiments. Two additional modes with similar structure are observed at St = 0.45 and St = 0.6, suggesting that the observed buffet might involve triadic mode interactions , rather than being a single global mode
Multiblock structured grids for direct numerical simulations of transonic wing sections
No full textDirect numerical simulations of transitional and turbulent flows around airfoils at moderate and high Reynolds number require large and complex grids consisting of billions of grid points. Advances in computational resources towards exa-scale computing (1018 floating point operations per second) and powerful algorithms that aim to exploit the full potential of modern high-performance computing architectures allow an increase of size and complexity of such simulations. However, high-order numerical methods for structured curvilinear grids require continuous metric terms up to the second order of derivatives or higher. An evaluation of the requirements on grid-generation tools, stressing scalability, precision and flexibility, suggested the need for handcrafted grids. In the present contribution, we outline a method based on polynomial functions and identify the benefits of such techniques for large structured multi-block high-fidelity grid generation around airfoil geometries, also providing an open-source tool for airfoils with sharp as well as blunt trailing edges
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
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
Wide domain simulations of flow over an unswept laminar wing section undergoing transonic buffet
No full textTransonic buffet is an unsteady flow phenomenon that limits the safe flight envelope of modern aircraft. Scale-resolving simulations with span-periodic boundary conditions can provide detailed insight into the flow physics associated with buffet and can help to calibrate simplified models that are needed, for example, to develop more efficient wings based on laminar-flow supercritical sections.However, such simulations are often feasible only for severely restricted spanwise domains. In the current contribution, we analyse an unswept laminar-flow wing section (of Dassault Aviation’sV2C profile) at a moderate Reynolds number of Re = 500,000 and a Mach number of M = 0.7 with spanwise domains equal to 5% and 100% of the airfoil chord. An implicit large-eddy simulation methodology, using a spectral error estimator to control the action of a high-order filter, is first validated against direct numerical simulations and then used for the domain width study.Quantitative differences, due to domain size, include an increase in amplitude and regularity of the buffet oscillations in the wider domain. Nevertheless, space-time analysis shows that key physical phenomena such as upstream-propagating shock waves are properly represented in the narrow domain and there is limited sensitivity to domain size of the aerodynamic coefficients. Even in the very wide domain, which is an order of magnitude wider than the largest turbulent structures measured at the trailing edge, certain features remain two-dimensional, including the shock and expansion waves that interact with the boundary layer upstream of transition. The transition mechanism is found to have subtle variations during a typical buffet cycle, with Kelvin-Helmholtzstructures prominent during low-lift phases and oblique modes developing behind shock/boundarylayer interactions during high-lift phases. The availability of the wide-domain data is used for further study of the buffet mechanism, considering phase-averaged data and instantaneous flow fields to show the global structure of the buffet oscillation
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