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.

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.

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.

Application of Air Microblowing Through a Porous Wall for Skin Friction Reduction on a Flat Plate

2010 ◽  
Vol 5 (3) ◽  
pp. 38-46
Author(s):  
Vladimir I. Kornilov ◽  
Andrey V. Boiko
Keyword(s):  
Boundary Layer ◽  
Flat Plate ◽  
Skin Friction ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Porous Wall ◽  
Friction Reduction ◽  
Local Skin ◽  
Skin Friction Reduction

The effect of air microblowing through a porous wall on the properties of a turbulent boundary layer formed on a flat plate in an incompressible flow is studied experimentally. The Reynolds number based on the momentum thickness of the boundary layer in front of the porous insert is 3 900. The mass flow rate of the blowing air per unit area was varied within Q = 0−0.0488 кg/s/m2 . A consistent decrease in local skin friction, reaching up to 45−47 %, is observed to occur at the maximal blowing air mass flow rate studied.

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

Influence of large-scale motions on the frictional drag in a turbulent boundary layer

2017 ◽  
Vol 829 ◽  
pp. 751-779 ◽  
Author(s):  
Jinyul Hwang ◽  
Hyung Jin Sung
Keyword(s):  
Boundary Layer ◽  
Skin Friction ◽  
Large Scale ◽  
Wall Region ◽  
Local Skin ◽  
Velocity Fluctuations ◽  
Vortical Structures ◽  
Change Of Scale ◽  
Local Skin Friction ◽  
Near Wall

Direct numerical simulation data of a turbulent boundary layer ($Re_{\unicode[STIX]{x1D70F}}=1000$) were used to investigate the large-scale influences on the vortical structures that contribute to the local skin friction. The amplitudes of the streamwise and wall-normal swirling strengths ($\unicode[STIX]{x1D706}_{x}$and$\unicode[STIX]{x1D706}_{y}$) were conditionally sampled by measuring the large-scale streamwise velocity fluctuations ($u_{l}$). In the near-wall region, the amplitudes of$\unicode[STIX]{x1D706}_{x}$and$\unicode[STIX]{x1D706}_{y}$decreased under negative$u_{l}$rather than under positive$u_{l}$. This behaviour arose from the spanwise motions within the footprints of the large-scale low-speed ($u_{l}<0$) and high-speed structures ($u_{l}>0$). The intense spanwise motions under the footprint of positive$u_{l}$noticeably strengthened the small-scale spanwise velocity fluctuations ($w_{s}$) below the centre of the near-wall vortical structures as compared to$w_{s}$within the footprint of negative$u_{l}$. The streamwise and wall-normal components were attenuated or amplified around the modulated vortical motions, which in turn led to the dependence of the swirling strength on the$u_{l}$event. We quantified the contribution of the modulated vortical motions$\langle -w\unicode[STIX]{x1D714}_{y}\rangle$, which were related to a change-of-scale effect due to the vortex-stretching force, to the local skin friction. In the near-wall region, intense values of$\langle -w\unicode[STIX]{x1D714}_{y}\rangle$were observed for positive$u_{l}$. By contrast, these values were low for negative$u_{l}$, in connection with the amplification of$w_{s}$and$\unicode[STIX]{x1D706}_{y}$by the strong spanwise motions of the positive$u_{l}$. The resultant skin friction induced by the amplified vortical motions within$u_{l}^{+}>2$was responsible for 15 % of the total skin friction generated by the change-of-scale effect. Finally, we applied this analysis to a drag-reduced flow and found that the amplified vortical motions within the footprint of positive$u_{l}$were markedly diminished, which ultimately contributed to the total drag reduction.

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