Large-Eddy-Simulations of Turbulent Wall Bounded Flow with and without Adverse Pressure Gradient

2003 ◽  
pp. 272-284
Author(s):  
S. Eisenbach ◽  
M. Manhart ◽  
R. Friedrich
Keyword(s):  
Pressure Gradient ◽  
Adverse Pressure Gradient ◽  
Large Eddy Simulations ◽  
Large Eddy ◽  
Turbulent Wall

The Turbulent Wall Jet in an Arbitrary Pressure Gradient

1969 ◽  
Vol 20 (1) ◽  
pp. 25-56 ◽  
Author(s):  
I. S. Gartshore ◽  
B. G. Newman
Keyword(s):  
Boundary Layer ◽  
Pressure Gradient ◽  
Practical Interest ◽  
Adverse Pressure Gradient ◽  
Wall Jet ◽  
Mean Velocity ◽  
Momentum Coefficient ◽  
Large Eddy ◽  
Trailing Edge Flap ◽  
Turbulent Wall

SummaryA method for calculating the growth of a turbulent wall jet in streaming flow has been developed. The flow is assumed to be two-dimensional, incompressible and over a plane, smooth wall. Downstream variations of pressure are permitted and separation in an adverse pressure gradient may be predicted. The method incorporates procedures for matching the flow to that at the blowing slot, although it is postulated that the upstream boundary layer there is thin enough that the wall jet develops without an unmixed wake (i.e. there is not a minimum in the mean-velocity profile).The method incorporates four integral momentum equations taken from the wall to various points in the flow. The calculation of the outer shearing stress, although empirical, is based on the large-eddy equilibrium hypothesis and therefore has some foundation. The remaining empiricism in the method is based on measurements in self-preserving wall jets.The method has been used to predict the jet-momentum coefficient required to suppress separation over a trailing-edge flap attached to a thin aerofoil. Plausible curves have been obtained Using assumed values of upstream boundary layer at the slot. Of some practical interest is the indication that large savings in power are possible if the upstream boundary layer is removed. This indicates that blowing combined with upstream suction, or multiple-slot blowing, may give useful savings in the application of blowing to prevent separation.

Large-Eddy Simulation of Film Cooling in an Adverse Pressure Gradient Flow

2013 ◽  
Vol 135 (3) ◽  
Author(s):  
Martin Konopka ◽  
Wilhelm Jessen ◽  
Matthias Meinke ◽  
Wolfgang Schröder
Keyword(s):  
Pressure Gradient ◽  
Film Cooling ◽  
Gradient Flow ◽  
Adverse Pressure Gradient ◽  
Streamwise Velocity ◽  
Co2 Injection ◽  
Pressure Gradients ◽  
Cooling Effectiveness ◽  
Turbulent Schmidt Number ◽  
Large Eddy

In order to analyze the interaction of multiple rows of film cooling holes in flows at adverse pressure gradients, large-eddy simulations (LESs) are performed. The considered three-row cooling configuration consists of inclined cooling holes at an angle of 30 deg with a lateral pitch of p/D=3 and a streamwise spacing of l/D=6. The cooling holes possess a fan-shaped exit geometry with lateral and streamwise expansions. For each cooling row the complete internal flow is computed. Air and CO2 are injected in order to investigate the influence of an increased density ratio on the film cooling physics at adverse pressure gradients. The CO2 injected at the same blowing rate as air shows a higher magnitude of the Reynolds shear stress component and, thus, an enhanced mixing downstream of the cooling holes. The LES results of the air and CO2 configurations are compared to the corresponding particle-image velocimetry (PIV) measurements and show a convincing agreement in terms of the averaged streamwise velocity and streamwise velocity fluctuations. Furthermore, the cooling effectiveness is investigated for a zero and an adverse pressure gradient configuration with a temperature ratio at gas turbine conditions. For the adverse pressure gradient case, reduced temperature levels off the wall are observed. However, the cooling effectiveness shows only minor differences compared to the zero pressure gradient flow. The turbulent Schmidt number at CO2 injection shows large variations. Just downstream of the injection it attains low values, whereas high values are detected in the upper mixing zone of the cooling flow and the freestream at each film cooling row.

A wall-layer model for large-eddy simulations of turbulent flows with/out pressure gradient

2011 ◽  
Vol 23 (1) ◽  
pp. 015101 ◽  
Author(s):  
C. Duprat ◽  
G. Balarac ◽  
O. Métais ◽  
P. M. Congedo ◽  
O. Brugière
Keyword(s):  
Pressure Gradient ◽  
Turbulent Flows ◽  
Wall Layer ◽  
Large Eddy Simulations ◽  
Layer Model ◽  
Large Eddy

Large-Eddy Simulation of Film Cooling in an Adverse Pressure Gradient Flow

2012 ◽  
Author(s):  
Martin Konopka ◽  
Wilhelm Jessen ◽  
Matthias Meinke ◽  
Wolfgang Schröder
Keyword(s):  
Pressure Gradient ◽  
Film Cooling ◽  
Gradient Flow ◽  
Adverse Pressure Gradient ◽  
Streamwise Velocity ◽  
Co2 Injection ◽  
Pressure Gradients ◽  
Cooling Effectiveness ◽  
Turbulent Schmidt Number ◽  
Large Eddy

To analyze the interaction of multiple rows of film cooling holes in flows at adverse pressure gradients large-eddy simulations (LES) are performed. The considered three-row cooling configuration consists of inclined cooling holes at an angle of 30° with a lateral pitch p/D = 3 and a streamwise spacing l/D = 6. The cooling holes possess a fan-shaped exit geometry with lateral and streamwise expansions. For each cooling row the complete internal flow was computed. Air and CO2 are injected to investigate the influence of an increased density ratio on the film cooling physics at adverse pressure gradients. CO2 injected at the same blowing rate as air shows a higher magnitude of the Reynolds shear stress component and thus an enhanced mixing downstream of the cooling holes. The LES results of the air and CO2 configurations are compared to the corresponding particle-image velocimetry (PIV) measurements and show a convincing agreement in terms of averaged streamwise velocity and streamwise velocity fluctuations. Furthermore the cooling effectiveness is investigated for a zero and an adverse pressure gradient configuration with a temperature ratio at gas turbine conditions. For the adverse pressure gradient case reduced temperature levels off the wall are observed. However, the cooling effectiveness shows only minor differences compared to the zero pressure gradient flow. The turbulent Schmidt number at CO2 injection shows large variations. Just downstream of the injection it attains low values, whereas high values are detected in the upper mixing zone of the cooling flow and the freestream at each film cooling row.

Large-eddy simulation of turbulent flow over a parametric set of bumps

2019 ◽  
Vol 866 ◽  
pp. 503-525 ◽  
Author(s):  
Racheet Matai ◽  
Paul Durbin
Keyword(s):  
Large Eddy Simulation ◽  
Turbulent Flow ◽  
Pressure Gradient ◽  
Separation Bubble ◽  
Adverse Pressure Gradient ◽  
Windward Side ◽  
Reynolds Stresses ◽  
Mean Flow ◽  
Eddy Simulation ◽  
Large Eddy

Turbulent flow over a series of increasingly high, two-dimensional bumps is studied by well-resolved large-eddy simulation. The mean flow and Reynolds stresses for the lowest bump are in good agreement with experimental data. The flow encounters a favourable pressure gradient over the windward side of the bump, but does not relaminarize, as is evident from near-wall fluctuations. A patch of high turbulent kinetic energy forms in the lee of the bump and extends into the wake. It originates near the surface, before flow separation, and has a significant influence on flow development. The highest bumps create a small separation bubble, whereas flow over the lowest bump does not separate. The log law is absent over the entire bump, evidencing strong disequilibrium. This dataset was created for data-driven modelling. An optimization method is used to extract fields of variables that are used in turbulence closure models. From this, it is shown how these models fail to correctly predict the behaviour of these variables near to the surface. The discrepancies extend further away from the wall in the adverse pressure gradient and recovery regions than in the favourable pressure gradient region.

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