Download pdf viscous drag reduction in boundary layers free. Solve problems involving laminar and turbulent boundary layers. At lower reynolds numbers, socalled secondorder effects vorticity inter. Viscous drag reduction in turbulent boundary layers has been an exceptionally interesting topic within fluid dynamics for several decades. Riblets are one of the methods used to reduce aircraft surface drag 14. The common mechanism of turbulent skinfriction drag. From boundary layers to the renormalization group john veysey ii and nigel goldenfeld department of physics, university of illinois at urbanachampaign, 1110 w. Reduction of turbulent boundary layer drag through dielectric. Your task will be to compare a set of di erent active drag reduction techniques in turbulent boundary layer. The field itself is rich with studies, efforts, failures and successes starting back from the 1950s. Boundary layers develop along the aerofoil shown above. Notably, the characteristic of the partial differential equations pde becomes parabolic, rather than.
This result suggests that the viscous effects are at play in the drag reduction for a turbulent boundary layer, in the sense that they compensate for the increase in wetted area. Green street, urbana, illinios 61801, usa published july 2007 the seemingly simple problem of determining the drag on a body moving through a very viscous. An examination of trapped bubbles for viscous drag reduction. The topics covered are laminar boundary layers, turbulent flows, nonplanar geometries, blowing and suction, polymer additives, and compliant surfaces. This volume authoritatively treats viscous drag reduction in four major categorieslaminar flow control, passive turbulent drag reduction, active turbulent drag reduction, and interactive turbulent drag reduction and presents emerging technologies, such as the use of surfactants, as an alternative to polymers. Of the various types of drag forces which arise, viscous, or skin friction, drag is one of the most important. Effect of drag reducing riblet surface on coherent structure. Click download or read online button to viscous drag reduction in boundary layers book pdf for free now. Pdf turbulent drag reduction by spanwise wall oscillations. The section on active turbulent drag reduction treats mhd flow drag reduction, drag reduction by polymers and surfactants, drag reduction by particle addition, and viscous drag reduction via surface mass injection. The mechanism of drag reduction seems to strongly relate to the spanwise vorticity generated by the periodic stokes layer over the oscillating wall, which affects the boundarylayer profile by.
Drag reduction, riblets, boundary layers, laminar, openfoam i. Reduction of the viscous shocklayer equations to boundarylayer equations i. Drag reduction schemes involving microbubble injection into turbulent boundary layers by madavan et al. It is shown that in the laminar boundary layer regime, the riblets are able to retard the viscous flow inside the grooves creating a cushion of stagnant fluid that the highspeed fluid above can partially slide over, thus reducing the shear stress inside the grooves and the total integrated viscous drag force on the plate. The paper deals with changes in the turbulent boundary layer resulting in frictional drag reduction. Drag reduction via turbulent boundary layer ow control. Reduction of the viscous shocklayer equations to boundary layer equations i. Reduction of viscous shocklayer equations to boundary layer. The surface texture, including riblets, dimples and roughness, has been actively investigated since 1980s due to their viscous drag reduction effect. The extent to which this condition modi es the general character of the. Evaluation of skin friction drag reduction in the turbulent. Drag reduction of turbulent boundary layers by means of grooved surfaces.
At various levels of modeling the featuring physical phenomena will be described. Introduction the classical boundarylayer theory applies only if the reynolds number is sufficiently high. The skin friction drag originating from fluid viscosity on surfaces of vehicles has a. Drag reduction of turbulent boundary layers by means of grooved surfaces citation for published version apa. Boundary layers and separation applied computational fluid. Twodimensional laminar boundary layers 1 introduction. Reduction of viscous drag has therefore been the object of many recent studies. Turbulent boundarylayer control with plasma actuators. For example, it can comprise up to 50% of the total drag on an aircraft in the cruise condition. Pdf viscous drag reduction in boundary layers download. Reduction of turbulent boundary layer drag through. A model for large eddy contributions in incompressible turbulent boundary layers. Exact equations for the velocity profile in the viscous boundary layer were derived by stokes in. Introduction the concept of achieving frictional drag reduction at high reynolds numbers using riblets.
A cross sectional view shows the layer at the top and the bottom creating a symmetrical profile. Boundary layers develop along the walls in pipe flow. Viscous drag reduction in boundary layers progress in. This volume authoritatively treats viscous drag reduction in four major categorieslaminar flow control, passive turbulent drag reduction, active. In aerodynamics, separation is usually undesirable because it increases drag, as we will see in chapter 8. Drag reduction of a turbulent boundary layer using plasma. The present volume discusses the development status of stability theory for laminar flow control design, applied aspects of laminarflow technology, transition.
Viscous drag reduction proceedings of the symposium on. Using an order of magnitude analysis, the wellknown governing navierstokes equations of viscous fluid flow can be greatly simplified within the boundary layer. Drag reduction by riblets philosophical transactions of. Viscous drag reduction proceedings of the symposium on viscous drag reduction held at the ltv research center, dallas, texas, september 24 and 25, 1968.
In the general case of particles immersed in a viscous fluid, forces do not cause acceleration but lead to a final velocity v so that the intensity of the force f is balanced by the resistance r vd i. The drag force is due to the pressure and shear forces acting on the surface of the object. Boundary layer combustion for viscous drag reduction in. Structure of turbulent boundary layers at maximum drag. Viscous drag reduction in boundary layersedited by dennis m. In recent years, turbulent boundary layer drag reduction has become an important area of fluid dynamics research.
Reduction of ship resistance through induced turbulent boundary layers by kevin joseph donnelly bachelors of science ocean engineering florida institute of technology 2009 a thesis submitted to the florida institute of technology in partial fulfillment of the requirements of the degree of master of science in ocean engineering melbourne, florida. Boundary layers are caused by diffusion of momentum. Viscous drag reduction in boundary layers aiaa arc. Explain the concept of momentum thickness and displacement thickness. Skin friction reduction in hypersonic turbulent flow by. The ow conditions and numerical methods are outlined in section ii. Viscous drag reduction in boundary layers download viscous drag reduction in boundary layers ebook pdf or read online books in pdf, epub, and mobi format. Viswanath experimental aerodynamics division, national aerospace laboratories, bangalore 560 017, india abstract the last two decades have seen considerable research activity on the use of riblets for viscous drag reduction. Drag reduction by riblets philosophical transactions of the.
Library of congress cataloging in publication data. Introduction fluid viscous drag includes two parts. Specifically, rising fuel costs greatly emphasized the usefulness and necessity of developing efficient viscous drag reduction methods. An examination of trapped bubbles for viscous drag.
The flow in the middle is fastest since it has not been slowed by the momentum transfer in the boundary layers. A brief overview of each area is provided by a recognized authority to highlight both relevant prior work and. Download pdf viscous drag reduction in boundary layers book full free. Drag reduction using wrinkled surfaces in high reynolds. Many of these techniques have been considered in the literature, but often only for turbulent channel ow. Structure of turbulent boundary layers at maximum drag reduction. Drag reduction by means of dimpled surfaces in turbulent. The mechanism of drag reduction seems to strongly relate to the spanwise vorticity generated by the periodic stokes layer over the oscillating wall, which affects the boundary layer profile by. Introduction the classical boundary layer theory applies only if the reynolds number is sufficiently high. Concerning aircraft efficiency relevant to the present research a reduction in aircraft drag of 10%, a reduction in aircraft fuel consumption of 30%, and a reduction in airframe, engine and system weight of 20% are envisaged. Friction drag is dominant in flow past a flat plate and is given by the surface shear stress times the area. M system for viscous drag reduction caltech thesis. Thus, viscous drag reduction of turbulent boundary layer has received widespread attention.
Two model boats were created, a control an unmodified model and the experiment hull one. Streamwise variations of turbulence statistics up to maximum drag reduction state in turbulent boundary layer flow due to surfactant injection. The tangential shear stresses acting on the object produce friction drag or viscous drag. Riblets only lead to a drag reduction within the turbulent boundary layer while there height is within the viscous sublayer. Turbulence, drag reduction, riblets, boundary layers, skin friction. Discuss the drag on bluff objects including long cylinders and spheres. Aug 20, 2016 direct force measurements and particle image velocimetry piv were used to investigate the drag and flow structure caused by surfaces with patterns of shallow spherical dimples with rounded edges subject to turbulent boundary layers. Skin friction drag is the frictional shear force exerted on a body aligned parallel to the flow, and therefore a direct result of the viscous boundary layer. It is shown that, for a given geometry and size of the surface microtexture in wall units, the drag reduction performance of microtextured surfaces degrades with increasing bulk reynolds number of the flow. Boundary layers, separation, and drag advanced fluid.
Sep 21, 2017 it is shown that in the laminar boundary layer regime, the riblets are able to retard the viscous flow inside the grooves creating a cushion of stagnant fluid that the highspeed fluid above can partially slide over, thus reducing the shear stress inside the grooves and the total integrated viscous drag force on the plate. Skinfriction drag reduction of up to 25 per cent was obtained from this technique. A brief overview of each area is provided by a recognized authority to highlight both relevant prior work and the importance of the paper to the drag reduction field. Reduction of viscous shocklayer equations to boundary. The deduction of the boundary layer equations was one of the most important advances in fluid dynamics.
In many situations involving flows of high reynolds number where inertial forces dominate over viscous forces, such as aircraft flight and the pipeline transportation of. In a boundary layer, however, viscous forces dominate over inertial forces. Due to the greater shear stress at the wall, the skin friction drag is greater for turbulent boundary layers than for laminar ones. Since the riblets have to be in the inner layer sublayer of the boundary layer in order to for the. As the lamina r boundary layer increases in thickness, it becomes unstable and.
In addition, a somewhat surprising experimental result was that heat transfer, rather than being increased, was slightly reduced by boundary layer combustion. Direct numerical simulations of highspeed turbulent. Drag reduction in turbulent boundary layer via flow control. Extrapolation of drag reduction data from dns to high reynolds number flows of practical interest is discussed. The largest drag reduction was found at the highest tested reynolds number of 40,000 based. This volume authoritatively treats viscous drag reduction in four major categorieslaminar flow control, passive turbulent drag reduction, active turbulent drag reduction, and interactive turbulent drag reductionand presents emerging technologies, such. Pdf turbulent boundary layer control tblc for skinfriction drag reduction is a. Also treated are such active turbulent dragreduction technique applications as those pertinent to mhd flow drag reduction, as well as drag reduction in liquid boundary layers by gas injection, drag reduction by means of polymers and surfactants, drag reduction by particle addition, viscous drag reduction via surface mass injection, and interactive wallturbulence control. Pdf viscous drag reduction in boundary layers download full.
Viscous boundary layer an originally laminar flow is affected by. Drag reduction in turbulent boundary layers by inplane. Pdf drag reduction via turbulent boundary layer flow control. Drag reduction of turbulent boundary layers by means of. Separation of the boundary layers occurs whenever the flow tries to decelerate quickly, that is. Numerical supported design of continuously adapted riblets. Drag reduction of up to 4 % is found compared to a flat surface. At lower reynolds numbers, socalled secondorder effects vorticity inter action, displacement, curvature, slip, and temperature. The proposed project drag reduction via turbulent boundary layer flow control dragy will approach the problem of turbulent drag reduction through the investigation of activepassive flowcontrol techniques to manipulate the drag produced by the flow structures in turbulent boundary layers. Boundary layer concepts henryk kudela contents 1 introduction. Download pdf viscous drag reduction in boundary layers. The parameters that determine the optimum performance of a given riblet are its optimum size and the slope of the drag curve in the viscous. Viscous drag reduction in boundary layers available for download and read online in other formats.
Direct force measurements and particle image velocimetry piv were used to investigate the drag and flow structure caused by surfaces with patterns of shallow spherical dimples with rounded edges subject to turbulent boundary layers. It is shown that in the laminar boundary layer regime the riblets are able to retard the viscous flow inside the grooves creating a cushion of stagnant fluid which the. Overall, this drag reduction technique has demonstrated a reduction in the vehicles net power requirement. Experimental findings around coherent vortical structures cvs in turbulent boundary layers and methods of controlling them static and dynamic mechanical characteristics of elastic composite coatings, as well as new techniques and devices developed for their measurement combined methods of flow control and drag reduction, including the effect of injection of polymer solutions, elastic coatings and generated longitudinal vortical structures on hydrodynamic resistance. The application of riblets within a laminar boundary layer would have a comparable impact as the application of a surface roughness increasing the overall viscous drag indinger 1999. Experiments are described, showing a remarkable decrease in friction coefficients for dilute. Find materials for this course in the pages linked along the left.
Viscous flow drag reduction progress in astronautics and. Also, numerical methods to solve the equations of motion in the boundary layer are discussed. Effect of drag reducing riblet surface on coherent. Experiments were conducted in the t4 stalker tube to study the effects of these. When a viscous uid ows along a xed impermeable wall, or past the rigid surface of an immersed body, an essential condition is that the velocity at any point on the wall or other xed surface is zero.
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