111 research outputs found
Dataset in support of the publication: On the co-existence of transonic buffet and separation-bubble modes for the OALT25 laminar-flow wing section
No full textData-set corresponding to the publication:
"On the co-existence of transonic buffet and separation-bubble modes for the OALT25 laminar-flow wing section"
Markus Zauner, Pradeep Moise, Neil D. Sandham
Journal of Flow Turbulence and Combustion (2023)
10.1007/s10494-023-00415-4
https://link.springer.com/article/10.1007/s10494-023-00415-4</span
Dataset for modal analysis of a laminar-flow airfoil under buffet conditions at Re=500,000
No full textDataset containing pertinent data of
"Modal analysis of a laminar-flow airfoil under buffet conditions at Re=500,000.",
M. Zauner and N. D. Sandham, Flow, Turbulence and Combustion, 2019, DOI: 10.1007/s10494-019-00087-z</span
Dataset for wide domain simulations of flow over an unswept laminar wing section undergoing transonic buffet
No full textThis dataset corresponds to the publication: Wide domain simulations of flow over an unswept laminar wing section undergoing transonic buffet by M. Zauner & N.D. Sandham in Physical Review Fluids, 2020.
This data-set contains the source code to compile the SE-ILES grid (it was not possible to include DassaultAviation’s V2C profile), a python code for two-point correlation, data corresponding to figures 2, 3, 4, 5, 6, 8, 9, 13, and animations. The latter includes histories of aerodynamic coefficients, unsteady data to generate x-t plots for surface pressure or at a monitor curve outside the boundary layers.
Note: .dat files are written in ASCII format and can be read by tecplot.</span
Dataset for direct numerical simulations of a transonic airfoil at a Reynolds number of Re=500,000
No full textThese three folders comprise datasets corresponding to figure 5, figure 6 and figure 8 in Zauner et al. (2018):
M. Zauner, N. De Tullio and N. Sandham,
"Direct numerical simulations of transonic flow around an airfoil at moderate Reynolds numbers." in the AIAA Journal, 2018. https://doi.org/10.2514/1.J057335
All simulations were carried out at a Mach number of M=0.7 and a Reynolds number of Re=500,000.
Description of content:
- Fig5: Average skin-friction coefficient and pressure coefficient as a function of axial chord position.
- Fig6: Skin friction as a function of time and space for the reference solution (case C0), the simulation with a grid refined in the xy-plane (G1) and the simulation with the reference xy-plane refined in the spanwise direction (G2).
- Fig8: Instantaneous lift coefficient and surface density as function of time. The surface density is recorded at 10%, 30%, 50%, 70% of the axial chord length and at the leading- as well as trailing edge.
- Movie showing vorticity contours in red and blue, and strong pressure gradients in the background.</span
Error severity values from simulations of a Taylor-Green vortex and a V2C aerofoil, computed using an error indicator
No full textThese two datasets comprise output from an (integer-valued) error indicator described by Jacobs et al. (2018):
Christian T. Jacobs, Markus Zauner, Nicola De Tullio, Satya P. Jammy, David J. Lusher, Neil D. Sandham,
"An error indicator for finite difference methods using spectral techniques with application to aerofoil simulation" in Computers & Fluids, 2018
DOI: https://doi.org/10.1016/j.compfluid.2018.03.065
- Taylor_green_vortex: Error indicator output from a Taylor-Green vortex simulation with grid sizes N = 32^3, 64^3, 128^3, 256^3.
- Aerofoil: Error indicator output from two simulations of flow past a V2C aerofoil profile, using coarse ("old") and refined ("new") grids. The solution files are also provided in binary format
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Direct numerical simulation and stability analysis of transonic flow around airfoils at moderate Reynolds numbers
No full textThe performance of turbomachinery components and the safe flight envelope of next-generation aircraft is often limited by complex transonic flow phenomena. Since the first flights close to sonic speeds, experiments have been carried out to explore the origin of flutter phenomena, supplemented with simulations of the Reynolds-averaged Navier-Stokes equations that are dependent on turbulence models. To date, direct numerical studies of low-frequency phenomena have been limited to low Reynolds numbers. The present work explores the transonic flow regime around Dassault Aviation’s V2C laminar-flow profile at moderate Reynolds numbers, and also analyses boundary-layer instabilities on a high-pressure turbine vane. Direct numerical simulations of an un-swept wing section are carried out at Mach 0.7 and an angle of attack of 4◦ using the in-house code SBLI, which is a well-validated high-order finite-difference flow solver. While the flow at Reynolds numbers of Re = 200,000 is purely subsonic, a significant supersonic region is observed for Re ≥ 500,000. Whereas experimental investigations of the same airfoil at higher Reynolds numbers showed single shock waves, the present reference case at Re = 500,000 exhibits continuously upstream-propagating shock waves. Besides laminar/turbulent boundary-layer transition and acoustic phenomena, a low-frequency phenomenon, known as transonic buffet, is studied. In addition to spectral analyses of the flow, linear stability analysis and a dynamic mode decomposition method are used to study flow phenomena apparent at different frequency ranges between Strouhal numbers of St ≈ 20 (Kelvin-Helmholtz instabilities) and St = 0.12 (transonic buffet). Resolution of small-scale structures is established by a grid convergence study and also employing spectral error indicators to assess the grid quality. The flow characteristics are also confirmed by a simulation with a five times wider spanwise domain size (25% of the chord length) comprising more than five billion grid points. A key observation of this work is the clear distinction between an acoustic mechanism associated with the shock-wave motion (St ≈ 0.5) and a quasi-periodic mode at significantly lower frequencies causing strong fluctuations in the aerodynamic lift (St ≈ 0.12). The Strouhal number of the low-frequency phenomenon agrees well with the buffet frequency in experiments at higher Reynolds numbers
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
Data supporting the article, "Transonic buffet characteristics under conditions of free and forced transition" published in the AIAA Journal, 2022
No full textThis dataset supports the publication by Moise, P., Zauner, M., Sandham, N. D., Timme, S. & Wei, H "Transonic Buffet Characteristics Under Conditions of Free and Forced Transition", AIAA Journal, https://doi.org/10.2514/1.J062362.
The data contains
DataSets.zip, containing ".csv" (comma separated values, CSV) files in ASCII format. These CSV files correspond to several plots presented in the article, "Transonic Buffet Characteristics Under Conditions of Free and Forced Transition" published in the AIAA Journal, 2022. Plots with aerofoil geometry are not provided due to copyright reasons. All CSV files are named in a "fig[No][subfigure][description].csv" format (e.g. fig30d_X.csv refers to figure 30d in the article with X being the variable stored). The figures for which data is provided are:
3,6,7,8,11,12,13,18,A1,B1.
A sample MATLAB script, sample Code.m is provided for plotting the data in the .csv files.
Padeep Moise is an Assistant Professor, Department of Aerospace Engineering, Indian Institute of Technology Kanpur, Uttar Pradesh 208016, India (email [email protected])
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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
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
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