Numerical Simulations of Equivalent Acoustic Sources Generation and Propagation Over a 2D High-Lift Wing in an Heterogeneous Mean Flow

2007 ◽  
Author(s):  
Ciprian Mincu ◽  
Stéphane Redonnet ◽  
Guillaume Desquesnes ◽  
Eric Manoha
Keyword(s):  
Numerical Simulations ◽  
Mean Flow ◽  
High Lift ◽  
Acoustic Sources

Analytical and Semi-empirical Models of Tornadoes and Downbursts

2021 ◽  
Author(s):  
Djordje Romanic ◽  
Horia Hangan
Keyword(s):  
Numerical Simulations ◽  
Stokes Equations ◽  
Empirical Models ◽  
Navier Stokes ◽  
Mean Flow ◽  
Navier Stokes Equations ◽  
Boundary Layer Equations ◽  
Simplifying Assumptions ◽  
The Individual ◽  
Semi Empirical

Analytical and semi-empirical models are inexpensive to run and can complement experimental and numerical simulations for risk analysis-related applications. Some models are developed by employing simplifying assumptions in the Navier-Stokes equations and searching for exact, but many times inviscid solutions occasionally complemented by boundary layer equations to take surface effects into account. Other use simple superposition of generic, canonical flows for which the individual solutions are known. These solutions are then ensembled together by empirical or semi-empirical fitting procedures. Few models address turbulent or fluctuating flow fields, and all models have a series of constants that are fitted against experiments or numerical simulations. This chapter presents the main models used to provide primarily mean flow solutions for tornadoes and downbursts. The models are organized based on the adopted solution techniques, with an emphasis on their assumptions and validity.

Prediction and Measurement of the Flow and Heat Transfer Along the Endwall and Within an Inlet Vane Passage

2002 ◽  
Author(s):  
Hugo D. Pasinato ◽  
Zan Liu ◽  
Ramendra P. Roy ◽  
W. Jeffrey Howe ◽  
Kyle D. Squires
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Numerical Simulations ◽  
Total Pressure ◽  
Solid Surfaces ◽  
Air Injection ◽  
Turbulent Heat ◽  
Mean Flow ◽  
Reynolds Analogy

Numerical simulations and laboratory measurements are performed to study the flow field and heat transfer in a linear cascade of turbine vanes. The vanes are scaled-up versions of a turbine engine inlet vane but simplified in that they are untwisted and follow the mid-span airfoil shape of the engine vane. The hub endwall is axially profiled while the tip endwall is flat. The hub endwall comprises the focus of the heat transfer investigation. Configurations are considered with and without air injection through three discrete angled (25 degrees to the main flow direction) slots upstream of each vane. The freestream turbulence intensity at the vane cascade inlet plane is 11 (± 2) percent, as measured by a single hot-wire placed perpendicular to the mean flow. The transient thermochromic liquid crystal technique is used to measure the convective heat transfer coefficient at the hub endwall for the baseline case (without air injection through the slots), and the heat transfer coefficient and cooling effectiveness at the same endwall for the cases with air injection at two blowing ratios. Miniature Kiel probes are used to measure the distribution of total pressure upstream of, within, and downstream of one vane passage. Numerical simulations are performed of the incompressible flow using unstructured grids. Hybrid meshes comprised of prisms near solid surfaces and tetrahedra away from the wall are used to resolve the solutions, with mesh refinement up to approximately 2 million cells. For all calculations, the first grid point is within one viscous unit of solid surfaces. A Boussinesq approximation is invoked to model the turbulent Reynolds stresses, with the turbulent eddy viscosity obtained from the Spalart-Allmaras one-equation model. The turbulent heat flux is modeled via Reynolds analogy and a constant turbulent Prandtl number of 0.9. The simulations show that endwall axial profiling results in flow reversal upstream of the vane, an effect that lowers the Stanton number for the baseline flow near the vane leading edge compared to our previous work in a flat-endwall geometry. Predictions of the total pressure loss coefficient show that the peak levels are higher than those measured.

Turbulent planar wakes under pressure gradient conditions

2017 ◽  
Vol 830 ◽  
Author(s):  
Sina Shamsoddin ◽  
Fernando Porté-Agel
Keyword(s):  
Pressure Gradient ◽  
Maximum Velocity ◽  
Wind Farms ◽  
Parameter Tuning ◽  
Momentum Equation ◽  
Mean Flow ◽  
Self Similarity ◽  
High Lift ◽  
Velocity Deficit ◽  
The Mean

Accurate prediction of the spatial evolution of turbulent wake flows under pressure gradient conditions is required in some engineering applications such as the design of high-lift devices and wind farms over topography. In this paper, we aim to develop an analytical model to predict the evolution of a turbulent planar wake under an arbitrary pressure gradient condition. The model is based on the cross-stream integration of the streamwise momentum equation and uses the self-similarity of the mean flow. We have also made an experimentally supported assumption that the ratio of the maximum velocity deficit to the wake width is independent of the imposed pressure gradient. The asymptotic response of the wake to the pressure gradient is also investigated. After its derivation, the model is successfully validated against experimental data by comparing the evolution of the wake width and maximum velocity deficit. The inputs of the model are the imposed pressure gradient and the wake width under zero pressure gradient. The model does not require any parameter tuning and is deemed to be practical, computationally fast, accurate enough, and therefore useful for the scientific and engineering communities.

scholarly journals Parametric forcing approach to rough-wall turbulent channel flow

2012 ◽  
Vol 712 ◽  
pp. 169-202 ◽  
Author(s):  
A. Busse ◽  
N. D. Sandham
Keyword(s):  
Numerical Simulations ◽  
Channel Flow ◽  
Stokes Equations ◽  
Rough Surfaces ◽  
Turbulent Channel Flow ◽  
Rough Wall ◽  
Force Term ◽  
Shape Functions ◽  
Mean Flow ◽  
The Mean

AbstractThe effects of rough surfaces on turbulent channel flow are modelled by an extra force term in the Navier–Stokes equations. This force term contains two parameters, related to the density and the height of the roughness elements, and a shape function, which regulates the influence of the force term with respect to the distance from the channel wall. This permits a more flexible specification of a rough surface than a single parameter such as the equivalent sand grain roughness. The effects of the roughness force term on turbulent channel flow have been investigated for a large number of parameter combinations and several shape functions by direct numerical simulations. It is possible to cover the full spectrum of rough flows ranging from hydraulically smooth through transitionally rough to fully rough cases. By using different parameter combinations and shape functions, it is possible to match the effects of different types of rough surfaces. Mean flow and standard turbulence statistics have been used to compare the results to recent experimental and numerical studies and a good qualitative agreement has been found. Outer scaling is preserved for the streamwise velocity for both the mean profile as well as its mean square fluctuations in all but extremely rough cases. The structure of the turbulent flow shows a trend towards more isotropic turbulent states within the roughness layer. In extremely rough cases, spanwise structures emerge near the wall and the turbulent state resembles a mixing layer. A direct comparison with the study of Ashrafian, Andersson & Manhart (Intl J. Heat Fluid Flow, vol. 25, 2004, pp. 373–383) shows a good quantitative agreement of the mean flow and Reynolds stresses everywhere except in the immediate vicinity of the rough wall. The proposed roughness force term may be of benefit as a wall model for direct and large-eddy numerical simulations in cases where the exact details of the flow over a rough wall can be neglected.

Direct numerical simulations of roughness-induced transition in supersonic boundary layers

2012 ◽  
Vol 693 ◽  
pp. 28-56 ◽  
Author(s):  
Suman Muppidi ◽  
Krishnan Mahesh
Keyword(s):  
Numerical Simulations ◽  
Shear Layer ◽  
Boundary Layers ◽  
Plate Boundary ◽  
Direct Numerical Simulations ◽  
Transition To Turbulence ◽  
Streamwise Vortices ◽  
Mean Flow ◽  
The Mean ◽  
Near Wall

AbstractDirect numerical simulations are used to study the laminar to turbulent transition of a Mach 2.9 supersonic flat plate boundary layer flow due to distributed surface roughness. Roughness causes the near-wall fluid to slow down and generates a strong shear layer over the roughness elements. Examination of the mean wall pressure indicates that the roughness surface exerts an upward impulse on the fluid, generating counter-rotating pairs of streamwise vortices underneath the shear layer. These vortices transport near-wall low-momentum fluid away from the wall. Along the roughness region, the vortices grow stronger, longer and closer to each other, and result in periodic shedding. The vortices rise towards the shear layer as they advect downstream, and the resulting interaction causes the shear layer to break up, followed quickly by a transition to turbulence. The mean flow in the turbulent region shows a good agreement with available data for fully developed turbulent boundary layers. Simulations under varying conditions show that, where the shear is not as strong and the streamwise vortices are not as coherent, the flow remains laminar.

Laboratory and numerical studies of baroclinic waves in an internally heated rotating fluid annulus: a case of wave/vortex duality?

1997 ◽  
Vol 337 ◽  
pp. 155-191 ◽  
Author(s):  
P. L. READ ◽  
S. R. LEWIS ◽  
R. HIDE
Keyword(s):  
Numerical Simulations ◽  
Potential Vorticity ◽  
Axisymmetric Flow ◽  
Zonal Flow ◽  
Chaotic Advection ◽  
Rotating Fluid ◽  
Mean Flow ◽  
Baroclinic Waves ◽  
Vortex Merging ◽  
Flow Components

The structure, transport properties and regimes of flow exhibited in a rotating fluid annulus, subject to internal heating and sidewall cooling, are studied both in the laboratory and in numerical simulations. The performance of the numerical model is verified quantitatively to within a few per cent in several cases by direct comparison with measurements in the laboratory of temperature and horizontal velocity fields in the axisymmetric and regular wave regimes. The basic azimuthal mean flow produced by this distribution of heat sources and sinks leads to strips of potential vorticity in which the radial gradient of potential vorticity changes sign in both the vertical and horizontal directions. From diagnosis of the energy budget of numerical simulations, the principal instability of the flow is shown to be predominantly baroclinic in nature, though with a non-negligible contribution towards the maintenance of the non-axisymmetric flow components from the barotropic wave–zonal flow interaction. The structure of the regime diagram for the internally heated baroclinic waves is shown to have some aspects in common with conventional wall-heated annulus waves, but the former shows no evidence for time-dependence in the form of ‘amplitude vacillation’. Internally heated flows instead evidently prefer to make transitions between wavenumbers in the regular regime via a form of vortex merging and/or splitting, indicating a mixed vortex/wave character to the non-axisymmetric flows in this system. The transition towards irregular flow occurs via a form of wavenumber vacillation, also involving vortex splitting and merging events. Baroclinic eddies are shown to develop from an initial axisymmetric flow via a mixed sinuous/varicose instability, leading to the formation of detached vortices of the same sign as the ambient axisymmetric potential vorticity at that level, in a manner which resembles recent simulations of atmospheric baroclinic frontal instability and varicose barotropic instabilities. Dye tracer experiments confirm the mixed wave/vortex character of the equilibrated instabilities, and exhibit chaotic advection in time-dependent flows.

scholarly journals Numerical simulations of streamwise vortices on a high-lift wing

2016 ◽  
Vol 8 (1) ◽  
pp. 3-15 ◽  
Author(s):  
T. Landa ◽  
R. Radespiel ◽  
J. Wild
Keyword(s):  
Numerical Simulations ◽  
Streamwise Vortices ◽  
High Lift

scholarly journals THE INFLUENCE OF THE TURBULENCE CLOSURE MODEL ON WAVE-CURRENT INTERACTION MODELING AT A LOCAL SCALE AT A LOCAL SCALE

2012 ◽  
Vol 1 (33) ◽  
pp. 64
Author(s):  
Maria João Teles ◽  
António Pires-Silva ◽  
Michel Benoit
Keyword(s):  
Numerical Simulations ◽  
Turbulent Flows ◽  
Stokes Equations ◽  
Local Scale ◽  
Navier Stokes ◽  
Mean Flow ◽  
Navier Stokes Equations ◽  
Turbulence Effects ◽  
Interaction Modeling ◽  
Flow Components

An advanced CFD solver based on the RANS (Reynolds Averaged Navier-Stokes) equations is used to evaluate wave-current interactions through numerical simulations of combined wave-current free surface turbulent flows. The repercussions of various schemes for modeling turbulence effects is addressed with a special attention to the exchanges and fluxes of momentum and energy between the mean flow components and the wave (oscillatory) component. Numerical simulations are compared with experimental data from Klopman (1994).

scholarly journals Turbulent drag reduction by anisotropic permeable substrates – analysis and direct numerical simulations

2019 ◽  
Vol 875 ◽  
pp. 124-172 ◽  
Author(s):  
G. Gómez-de-Segura ◽  
R. García-Mayoral
Keyword(s):  
Drag Reduction ◽  
Numerical Simulations ◽  
Critical Value ◽  
Direct Numerical Simulations ◽  
Mean Flow ◽  
Turbulent Drag Reduction ◽  
Turbulent Drag ◽  
Theoretical Predictions ◽  
The Mean ◽  
The Difference

We explore the ability of anisotropic permeable substrates to reduce turbulent skin friction, studying the influence that these substrates have on the overlying turbulence. For this, we perform direct numerical simulations of channel flows bounded by permeable substrates. The results confirm theoretical predictions, and the resulting drag curves are similar to those of riblets. For small permeabilities, the drag reduction is proportional to the difference between the streamwise and spanwise permeabilities. This linear regime breaks down for a critical value of the wall-normal permeability, beyond which the performance begins to degrade. We observe that the degradation is associated with the appearance of spanwise-coherent structures, attributed to a Kelvin–Helmholtz-like instability of the mean flow. This feature is common to a variety of obstructed flows, and linear stability analysis can be used to predict it. For large permeabilities, these structures become prevalent in the flow, outweighing the drag-reducing effect of slip and eventually leading to an increase of drag. For the substrate configurations considered, the largest drag reduction observed is ${\approx}$20–25 % at a friction Reynolds number $\unicode[STIX]{x1D6FF}^{+}=180$.

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