Experimental Study on Skin Friction Reduction With Micro-Blowing

Volume 4 ◽  
2004 ◽  
Author(s):  
Song Liu ◽  
Hongmin Li ◽  
Minel J. Braun
Keyword(s):  
Boundary Layer ◽  
Shear Stress ◽  
Skin Friction ◽  
Full Range ◽  
Experimental System ◽  
Main Flow ◽  
Friction Reduction ◽  
Long Distance ◽  
Full Field ◽  
Set Up

Reducing skin friction, such as friction on a car hood or a plane wing, can significantly reduce the drag force and decrease specific fuel consumption. Many techniques and methods have been tried. The Micro-blowing Technique (MBT) is an innovative way to reduce skin friction. Suggested by early research in boundary layer injection in 1950s, MBT was actually brought to effective use in 1994 by Hwang [1]. The basic idea is that by blowing fluid, same as or different from the mainstream flow, at an angle with that of the main flow, a decrease in the velocity gradient at the wall can be achieved, and thus the shear stress on the surface is reduced. Although the experimental data on boundary layer with micro blowing show a significant friction reduction, the mechanism of MBT is still not well understood and thus its full range of application is not yet established. In this paper, we further the understanding of the MBT mechanism. An experimental system is set up to visualize the flow structure on a plate with and without micro blowing in a tunnel. A long distance microscope is combined with a Full Field Flow Tracking visualization method in order to elucidate the nature of the flow interaction and mixing between the blowing flow and the main flow. The flow above the porous plates is visualized and velocities both in the blowing layer immediately adjacent to the plate and in the main flow are quantified using the PIV procedure. The flow and shear stress analysis shows that MTB has significantly different effects on a flow with a boundary layer and fully developed internal flows.

scholarly journals Research on Skin-Friction Drag Reduction by Hydrogen Injection in Supersonic Boundary Layer

2019 ◽  
Vol 37 (3) ◽  
pp. 449-456
Author(s):  
Shuai Wang ◽  
Guoqiang He ◽  
Fei Qin
Keyword(s):  
Boundary Layer ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Drag Reduction ◽  
Skin Friction ◽  
Friction Reduction ◽  
Confined Space ◽  
Friction Drag ◽  
Wall Shear ◽  
Friction Drag Reduction

In order to investigate the applicability of the skin-friction reduction technique using hydrogen injecting into turbulent boundary layer, three-dimensional numerical simulation was carried out for a constant-cross-confined-space with rearward facing steps. The flow characteristics near wall surface and development of wall shear stress were analyzed and compared under different coming flow and injection conditions. The simulation results show that the hydrogen injection can achieve around 13.5% skin-friction drag reduction under the coming flow Mach number of 2.3Ma or 2.8Ma. At 2.8Ma, the optimal reduction profit is 13.5% which is obtained when the equivalent ratio is 0.06. The gases mixings are gradually enhanced along the flow path. At the positions of shock wave-boundary-layer interactions, the mixings are first strengthened and then suppressed, and meanwhile, the wall shear stress and density changes with similar law that first decreases and then rebounds at the positions. The declines of skin-friction drag decrease along the flow direction, the best reduction area can profit nearly 60%.

The accelerated fully rough turbulent boundary layer

1977 ◽  
Vol 82 (3) ◽  
pp. 507-528 ◽  
Author(s):  
Hugh W. Coleman ◽  
Robert J. Moffat ◽  
William M. Kays
Keyword(s):  
Boundary Layer ◽  
Shear Stress ◽  
Turbulent Boundary Layer ◽  
Pressure Gradient ◽  
Stress Tensor ◽  
Skin Friction ◽  
Shape Factor ◽  
Reynolds Shear Stress ◽  
Smooth Wall ◽  
Mean Velocity

The behaviour of a fully rough turbulent boundary layer subjected to favourable pressure gradients both with and without blowing was investigated experimentally using a porous test surface composed of densely packed spheres of uniform size. Measurements of profiles of mean velocity and the components of the Reynolds-stress tensor are reported for both unblown and blown layers. Skin-friction coefficients were determined from measurements of the Reynolds shear stress and mean velocity.An appropriate acceleration parameterKrfor fully rough layers is defined which is dependent on a characteristic roughness dimension but independent of molecular viscosity. For a constant blowing fractionFgreater than or equal to zero, the fully rough turbulent boundary layer reaches an equilibrium state whenKris held constant. Profiles of the mean velocity and the components of the Reynolds-stress tensor are then similar in the flow direction and the skin-friction coefficient, momentum thickness, boundary-layer shape factor and the Clauser shape factor and pressure-gradient parameter all become constant.Acceleration of a fully rough layer decreases the normalized turbulent kinetic energy and makes the turbulence field much less isotropic in the inner region (forFequal to zero) compared with zero-pressure-gradient fully rough layers. The values of the Reynolds-shear-stress correlation coefficients, however, are unaffected by acceleration or blowing and are identical with values previously reported for smooth-wall and zero-pressure-gradient rough-wall flows. Increasing values of the roughness Reynolds number with acceleration indicate that the fully rough layer does not tend towards the transitionally rough or smooth-wall state when accelerated.

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.

Proposal of control laws for turbulent skin friction reduction based on resolvent analysis

2019 ◽  
Vol 866 ◽  
pp. 810-840 ◽  
Author(s):  
Aika Kawagoe ◽  
Satoshi Nakashima ◽  
Mitul Luhar ◽  
Koji Fukagata
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Drag Reduction ◽  
Skin Friction ◽  
Friction Reduction ◽  
Suboptimal Control ◽  
Spectral Space ◽  
Control Laws ◽  
Wall Shear ◽  
Skin Friction Reduction

This paper evaluates and modifies the so-called suboptimal control technique for turbulent skin friction reduction through a combination of low-order modelling and direct numerical simulation (DNS). In a previous study, Nakashima et al. (J. Fluid Mech., vol. 828, 2017, pp. 496–526) employed resolvent analysis to show that the efficacy of suboptimal control was mixed across spectral space when the streamwise wall shear stress (case ST) was used as a sensor signal, i.e. specific regions of spectral space showed drag increment. This observation suggests that drag reduction may be attained if control is applied selectively in spectral space. DNS results presented in the present study, however, do not show a significant effect on the flow with selective control. A posteriori analyses attribute this lack of efficacy to a much lower actuation amplitude in the simulations compared to model assumptions. Building on these observations, resolvent analysis is used to design and provide a preliminary assessment of modified control laws that also rely on sensing the streamwise wall shear stress. Control performance is then assessed by means of DNS. The proposed control laws generate as much as $10\,\%$ drag reduction, and these results are broadly consistent with resolvent-based predictions. The physical mechanisms leading to drag reduction are assessed via conditional sampling. It is shown that the new control laws effectively suppress the near-wall quasi-streamwise vortices. A physically intuitive explanation is proposed based on a separate evaluation of clockwise and anticlockwise vortices.

Numerical Simulation of Coaxial Evaporating Spray in Nozzle Region of Circulating Fluidized Reactor

2002 ◽  
Author(s):  
Chao Zhu ◽  
Xiaohua Wang ◽  
Guangliang Liu
Keyword(s):  
Circulating Fluidized Bed ◽  
Experimental System ◽  
Droplet Size Distribution ◽  
Numerical Code ◽  
Solid Flow ◽  
Full Field ◽  
Lagrangian Simulation ◽  
Solids Loading ◽  
Set Up ◽  
Evaporating Spray

Full field hydrodynamic mixing of a coaxial evaporating spray in the nozzle region of a circulating fluidized reactor was numerically investigated. An Eulerian-Lagrangian numerical code was developed for the field description of evaporating spray characteristics with strong phase interactions among evaporating droplets, solids and gas. The gas-solid flow is simulated using multi-fluid method coupled with kinetic theory modeling for inter-particle collisions while the spray is treated as the discrete droplets in a pseudo-continuum gas-solid flow. The Lagrangian simulation of the spray provides the needed coupling terms for the Eulerian simulation of gas-solid flows, such as droplet evaporation rate and interactions among phase of droplets, gas and solids. Phase distributions of temperature, velocity and concentration were achieved to explain the mixing process of evaporating spray in gas-solid flows. Effects of inlet solids loading and droplet size distribution on both spray structure and spray penetration depth were illustrated. An experimental system of liquid nitrogen spray into a circulating fluidized bed of fluid catalytic cracking particles is set up to provide experimental validation of our model. Good comparisons of the simulation and measurements are illustrated.

Cooling-Induced Depressurization of a Steam-Filled Chamber

2011 ◽  
Author(s):  
Pengfei He ◽  
Rajesh Patel ◽  
Chao Zhu ◽  
Chao-Hsin Lin
Keyword(s):  
Boundary Conditions ◽  
Saturated Vapor ◽  
Mechanistic Model ◽  
Experimental System ◽  
Pure Substance ◽  
Dynamics Modeling ◽  
Full Field ◽  
Parametric Effects ◽  
Coupled Boundary Conditions ◽  
Set Up

Depressurization can be realized by condensing saturated vapor of a pure substance inside a confined chamber. The depressurization rate depends directly upon the effectiveness of cooling to the condensing vapor. The objective of this study is to develop modeling approaches for cooling-controlled depressurization, which will assist the optimization of process design and operation. To this end, an experimental system is set up to provide sets of data for model validations. A simple mechanistic model based on assumption of thermodynamic-equilibrium inside the system has been developed to show the limiting depressurization characteristics with instant heat balance. This simplified model has a merit of quick evaluation on comparisons among various parametric effects. Yet the model is inadequate for real-time quantification in depressurization. The gaps between the measurements and model predictions indicate the importance of local non-uniform heat transfer and condensation. To close the gaps, a complicated full-field computational fluid dynamics modeling and simulation (CFD) is needed, in which the local condensations (especially surface condensation) must be fully account for. The difficulty in CFD approach is the unavailability of condensation-coupled boundary conditions in most commercial CFD codes. Hence, in this paper, we have also proposed the modeling of condensation-based boundary conditions that will be used for CFD simulations.

Active Control of Near-Wall Coherent Structures

2002 ◽  
Author(s):  
P. Konieczny ◽  
A. Bottaro ◽  
V. Monturet ◽  
B. Nogarede
Keyword(s):  
Boundary Layer ◽  
Skin Friction ◽  
Coherent Structures ◽  
Large Scale ◽  
Travelling Wave ◽  
Friction Reduction ◽  
Wall Turbulence ◽  
Integral Control ◽  
Macroscopic Simulation ◽  
Near Wall

This work aims at finding efficient means to reduce skin friction drag in a turbulent boundary layer. The argument on which the study is based is that turbulence exists near a wall because of the presence of an autonomous cycle which is maintained even in the absence of forcing from the free-stream. The central elements of this cycle are the near-wall coherent structures whose dynamics control the turbulence production. It is postulated that an action at the wall capable of disrupting the turbulent wall-cycle can yield a significant skin friction reduction. A model cycle is produced by embedding artificial, large scale streamwise vortices and streaks in a Blasius boundary layer. A control is then conceived, meant to produce an agglomeration of the streaks to hamper the cycle. The action envisaged consists in a movement of the wall, in the form of a spanwise standing or travelling wave of sufficiently long wavelength. The controllers in the present macroscopic simulation are simply cantilever beams whose movement is driven by ceramic piezo-actuators. Piezoelectric fibers realizing the same action (properly rescaled) provide, possibly, the answer to the technological challenge of the integral control of near-wall turbulence.

Sign in / Sign up

Export Citation Format

Share Document