Experience of the Using of Cascade Method for Turbulent Boundary-Layer Control Through Air Blowing

2014 ◽  
Vol 9 (1) ◽  
pp. 49-61
Author(s):  
Vladimir Kornilov ◽  
Ivan Kavun ◽  
Anatoliy Popkov
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Wind Tunnel Test ◽  
Barometric Pressure ◽  
Local Skin ◽  
Air Blowing ◽  
Ground Conditions ◽  
Local Skin Friction ◽  
The Difference ◽  
Cascade Method

The possibilities of turbulent drag reduction in an incompressible turbulent boundary layer of a flat plate with air blowing through a microperforated surface which consists of sequentially arranged one behind the other self-contained permeable areas were studied. Mass flow rate of air blowing per unit area Q was increased with increasing distance downstream, but in total was not more than 0.0768 kg/s/m2 . A consistent reduction of the local skin friction values along the length of the model, up to 70% at the end of the last active blowing area was shown. The experimental data characterizing the ability to manage a turbulent boundary layer in the ground conditions by passive air overflow generated by the difference between the barometric pressure and the pressure in the wind tunnel test section were obtained

scholarly journals Global effect of local skin friction drag reduction in spatially developing turbulent boundary layer

2016 ◽  
Vol 805 ◽  
pp. 303-321 ◽  
Author(s):  
A. Stroh ◽  
Y. Hasegawa ◽  
P. Schlatter ◽  
B. Frohnapfel
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Drag Reduction ◽  
Control Region ◽  
Reduction Rate ◽  
Wall Turbulence ◽  
Local Skin ◽  
Control Schemes ◽  
Local Skin Friction ◽  
Friction Drag Reduction

A numerical investigation of two locally applied drag-reducing control schemes is carried out in the configuration of a spatially developing turbulent boundary layer (TBL). One control is designed to damp near-wall turbulence and the other induces constant mass flux in the wall-normal direction. Both control schemes yield similar local drag reduction rates within the control region. However, the flow development downstream of the control significantly differs: persistent drag reduction is found for the uniform blowing case, whereas drag increase is found for the turbulence damping case. In order to account for this difference, the formulation of a global drag reduction rate is suggested. It represents the reduction of the streamwise force exerted by the fluid on a plate of finite length. Furthermore, it is shown that the far-downstream development of the TBL after the control region can be described by a single quantity, namely a streamwise shift of the uncontrolled boundary layer, i.e. a changed virtual origin. Based on this result, a simple model is developed that allows the local drag reduction rate to be related to the global one without the need to conduct expensive simulations or measurements far downstream of the control region.

Flat-Plate Skin Friction Under The Conditions Of Air Blowing Through A Wall With Intermittent In Length Permeability

2015 ◽  
Vol 10 (3) ◽  
pp. 48-62
Author(s):  
Vladimir Kornilov ◽  
Andrey Boiko ◽  
Ivan Kavun
Keyword(s):  
Boundary Layer ◽  
Flat Plate ◽  
Skin Friction ◽  
Unit Area ◽  
Friction Reduction ◽  
Local Skin ◽  
Air Blowing ◽  
Local Skin Friction ◽  
Incompressible Boundary ◽  
Skin Friction Reduction

Possibility of turbulent skin-friction reduction in an incompressible boundary layer of a flat plate with air blowing through a microperforated surface consisting of alternating permeable and impermeable sections was studied experimentally and computationally. The mass flow rate of the air per unit area was varied in the range from 0 to 0.0709 kg/s/m2 , which corresponds to the maximum blowing coefficient equal to 0.00344. A consistent reduction of the local skin-friction values along the chord of the microperforated insert was found, the reduction achieving nearly 70 % at the end of the last active blowing sections, except the impermeable surface sections demonstrating, on the contrary, the skin friction increase: the longer section, the higher skin friction.

Wind Tunnel Tests of Two Lucy Ashton Reflex Geosims

1970 ◽  
Vol 14 (04) ◽  
pp. 241-276
Author(s):  
P. N. Joubert ◽  
N. Matheson
Keyword(s):  
Boundary Layer ◽  
Wind Tunnel ◽  
Turbulent Boundary Layer ◽  
Flat Plate ◽  
Skin Friction ◽  
Viscous Drag ◽  
Two Dimensional ◽  
Local Skin ◽  
Wind Tunnel Tests ◽  
Local Skin Friction

A 9-ft and a 4½-ft reflex model of the Lucy Ashton were tested in a wind tunnel. Both pins and wires were used as stimulators to promote a turbulent boundary layer. The effects of the stimulators could be taken into account by considering the virtual origin of the turbulent boundary layer. Slightly different viscous drag curves were found for each model, both with a slope much steeper than previously anticipated. The skin friction was determined using two independent methods. Large increases and deficits in local skin friction coefficients were found at the bow and stern of the models respectively as compared with those for a two-dimensional flat plate.

Predicting Turbulent Boundary Layer Wall Pressure Fluctuations in Adverse Pressure Gradients

2005 ◽  
Author(s):  
Frank J. Aldrich
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Pressure Gradient ◽  
Pressure Fluctuations ◽  
Adverse Pressure Gradient ◽  
Wall Pressure ◽  
Prediction Tool ◽  
Pressure Gradients ◽  
Wall Pressure Fluctuations ◽  
The Difference

A physics-based approach is employed and a new prediction tool is developed to predict the wavevector-frequency spectrum of the turbulent boundary layer wall pressure fluctuations for subsonic airfoils under the influence of adverse pressure gradients. The prediction tool uses an explicit relationship developed by D. M. Chase, which is based on a fit to zero pressure gradient data. The tool takes into account the boundary layer edge velocity distribution and geometry of the airfoil, including the blade chord and thickness. Comparison to experimental adverse pressure gradient data shows a need for an update to the modeling constants of the Chase model. To optimize the correlation between the predicted turbulent boundary layer wall pressure spectrum and the experimental data, an optimization code (iSIGHT) is employed. This optimization module is used to minimize the absolute value of the difference (in dB) between the predicted values and those measured across the analysis frequency range. An optimized set of modeling constants is derived that provides reasonable agreement with the measurements.

The turbulent boundary layer over transverse square cavities

1999 ◽  
Vol 395 ◽  
pp. 271-294 ◽  
Author(s):  
L. DJENIDI ◽  
R. ELAVARASAN ◽  
R. A. ANTONIA
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Flow Direction ◽  
Reynolds Shear Stress ◽  
Local Maximum ◽  
Turbulent Energy ◽  
Skin Friction Coefficient ◽  
Reynolds Stresses ◽  
Smooth Wall ◽  
Local Skin

Laser-induced uorescence (LIF) and laser Doppler velocimetry (LDV) are used to explore the structure of a turbulent boundary layer over a wall made up of two-dimensional square cavities placed transversely to the flow direction. There is strong evidence of occurrence of outflows of fluid from the cavities as well as inflows into the cavities. These events occur in a pseudo-random manner and are closely associated with the passage of near-wall quasi-streamwise vortices. These vortices and the associated low-speed streaks are similar to those found in a turbulent boundary layer over a smooth wall. It is conjectured that outflows play an important role in maintaining the level of turbulent energy in the layer and enhancing the approach towards self-preservation. Relative to a smooth wall layer, there is a discernible increase in the magnitudes of all the Reynolds stresses and a smaller streamwise variation of the local skin friction coefficient. A local maximum in the Reynolds shear stress is observed in the shear layers over the cavities.

Sign in / Sign up

Export Citation Format

Share Document