Large-eddy simulations of the flow on an aerofoil with leading-edge imperfections

2021 ◽  
pp. 1-26
Author(s):  
Vishal Kumar ◽  
Ugo Piomelli ◽  
Oriol Lehmkuhl
Keyword(s):  
Leading Edge ◽  
Large Eddy Simulations ◽  
Large Eddy

Effect of Blowing Ratio in the Near-Stagnation Region of a Three-Row Leading Edge Film Cooling Geometry Using Large Eddy Simulations

2009 ◽  
Author(s):  
Sai Shrinivas Sreedharan ◽  
Danesh K. Tafti
Keyword(s):  
Film Cooling ◽  
Density Ratio ◽  
Leading Edge ◽  
Large Eddy Simulations ◽  
Stagnation Region ◽  
Stagnation Line ◽  
Blowing Ratio ◽  
Large Eddy ◽  
Adiabatic Effectiveness ◽  
Compound Angle

Computational studies are carried out using Large Eddy Simulations (LES) to investigate the effect of coolant to mainstream blowing ratio in a leading edge region of a film cooled vane. The three row leading edge vane geometry is modeled as a symmetric semi-cylinder with a flat afterbody. One row of coolant holes is located along the stagnation line and the other two rows of coolant holes are located at ±21.3° from the stagnation line. The coolant is injected at 45° to the vane surface with 90° compound angle injection. The coolant to mainstream density ratio is set to unity and the freestream Reynolds number based on leading edge diameter is 32000. Blowing ratios (B.R.) of 0.5, 1.0, 1.5, and 2.0 are investigated. It is found that the stagnation cooling jets penetrate much further into the mainstream, both in the normal and lateral directions, than the off-stagnation jets for all blowing ratios. Jet dilution is characterized by turbulent diffusion and entrainment. The strength of both mechanisms increases with blowing ratio. The adiabatic effectiveness in the stagnation region initially increases with blowing ratio but then generally decreases as the blowing ratio increases further. Immediately downstream of off-stagnation injection, the adiabatic effectiveness is highest at B.R. = 0.5. However, further downstream the larger mass of coolant injected at higher blowing ratios, in spite of the larger jet penetration and dilution, increases the effectiveness with blowing ratio.

scholarly journals Resolvent-analysis-based design of airfoil separation control

2019 ◽  
Vol 867 ◽  
pp. 572-610 ◽  
Author(s):  
Chi-An Yeh ◽  
Kunihiko Taira
Keyword(s):  
Leading Edge ◽  
Open Loop ◽  
Large Eddy Simulations ◽  
Control Input ◽  
Mean Flow ◽  
Actuation Frequency ◽  
Flow Modification ◽  
Large Perturbation ◽  
Large Eddy ◽  
Energy Amplification

We use resolvent analysis to design active control techniques for separated flows over a NACA 0012 airfoil. Spanwise-periodic flows over the airfoil at a chord-based Reynolds number of$23\,000$and a free-stream Mach number of$0.3$are considered at two post-stall angles of attack of$6^{\circ }$and$9^{\circ }$. Near the leading edge, localized unsteady thermal actuation is introduced in an open-loop manner with two tunable parameters of actuation frequency and spanwise wavelength. To provide physics-based guidance for the effective choice of these control input parameters, we conduct global resolvent analysis on the baseline turbulent mean flows to identify the actuation frequency and wavenumber that provide large perturbation energy amplification. The present analysis also considers the use of a temporal filter to limit the time horizon for assessing the energy amplification to extend resolvent analysis to unstable base flows. We incorporate the amplification and response mode from resolvent analysis to provide a metric that quantifies momentum mixing associated with the modal structure. This metric is compared to the results from a large number of three-dimensional large-eddy simulations of open-loop controlled flows. With the agreement between the resolvent-based metric and the enhancement of aerodynamic performance found through large-eddy simulations, we demonstrate that resolvent analysis can predict the effective range of actuation frequency as well as the global response to the actuation input. We believe that the present resolvent-based approach provides a promising path towards mean flow modification by capitalizing on the dominant modal mixing.

Flow Control of a Retreating Airfoil via NS-DBD Actuators Using Large Eddy Simulations

2014 ◽  
Author(s):  
Kelsey Shaler ◽  
Datta V. Gaitonde
Keyword(s):  
Flow Control ◽  
Shear Layer ◽  
Static Pressure ◽  
Leading Edge ◽  
Large Eddy Simulations ◽  
Surface Heating ◽  
Trailing Edge ◽  
Volumetric Heating ◽  
Large Eddy ◽  
Heating Model

The capability of Large Eddy Simulations (LES) to accurately model Nano-Second Pulsed Dielectric-Barrier Discharge (NS-DBD) plasma actuators for use as a flow control devise is demonstrated by comparing the newly-developed volumetric heating model to experimental results as well as a previously established surface heating model. The purpose of these models and corresponding experiments is to show that use of NS-DBD actuators can mitigate the presence of stall on a NACA0015 airfoil at a Reynolds number of 100,000 and 15° angle of attack in reversed-flow conditions. Actuators are placed at both the aerodynamic leading and trailing edge — the effects of which are analyzed separately — and forced at several Strouhal numbers StF=fc′U∞. The model validation is carried out by comparing the actuator pulse structure, mean value contours of various parameters, static pressure distribution (Cp) along the airfoil surface, and FFT plots of sound pressure level (SPL). The model results are then compared to the no-control simulations to provide evidence that actuation delays the onset of stall. This process is explored for both unsteady and steady quantities, including FFT plots, intantaneous flow field response, static pressure recovery, and mean quanitites, including a boundary layer analysis. It is concluded that at low Reynolds numbers reattachment occurs through enhanced turbulence of a separated, laminar shear layer; the reattachment processes is shown to take place over approximately 8 characteristic times for both actuator locations, although leading edge actuation only results in reattachment in the mean sense. Under similar situations, the volumetric and surfaec heating models showed similar recovery characteristics; however, since the volumetric model is less empirical than surface heating, it is recommended that volumetric heating be used in the future. Both heating models indicate that actuation at the aerodynamic leading edge has the greatest affect on the flow due to the laminar nature of the corresponding shear layer, as opposed to the turbulent shear layer on the trailing edge. It addition, a change in duty cycle was shown to have little effect on the results whereas an incerase in StF had a large negative effect on reattachment.

Large Eddy Simulations of a Three-Row Leading Edge Film Cooling Geometry

2008 ◽  
Author(s):  
Sai Shrinivas Sreedharan ◽  
Danesh K. Tafti
Keyword(s):  
Film Cooling ◽  
Lateral Displacement ◽  
Vortex Pair ◽  
Leading Edge ◽  
Large Eddy Simulations ◽  
Cylinder Surface ◽  
Stagnation Region ◽  
Single Vortex ◽  
Blowing Ratio ◽  
Large Eddy

A three-row leading edge film cooling geometry is investigated using Large-Eddy Simulations (LES) at a freestream Reynolds number of 32,000 and blowing ratio of 0.5 with lateral injection of 45° to the surface and 90° compound injection. The stagnation jet interacts with the mainstream through the generation of ring vortices which quickly breakdown and convect along the cylinder surface. The coolant penetrates the mainstream both laterally and normal to the surface resulting in increased mixing and turbulence generation. As the coolant loses transverse and lateral momentum it is pushed back to the surface in the stagnation region after which it convects downstream along the blade surface. Surface coverage is uniform but weak with spanwise-averaged effectiveness ranging from 0.1 to 0.3 in the stagnation region. The primary off-stagnation coolant and mainstream interaction is through the generation of a counter-rotating vortex pair in the immediate wake, but which quickly degenerates to a single vortex which entrains free-stream fluid near the surface at the aft-end of the jet. In contrast to the stagnation row, the coolant stays in close proximity to the surface and does not undergo a large lateral displacement along the spanwise pitch. As a consequence it provides good local coverage along its trajectory but barely covers half the lateral pitch. Hence, spanwise-averaged effectiveness is of the same order as at stagnation starting at 0.3 downstream of injection to 0.1 about 6d downstream.

Automotive Flow and Acoustic Predictions using Large Eddy Simulations

2012 ◽  
Vol 39 (3) ◽  
pp. 272-289 ◽  
Author(s):  
Bahram Khalighi ◽  
Gianluca Iaccarino ◽  
Yaser Khalighi
Keyword(s):  
Large Eddy Simulations ◽  
Large Eddy
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