Boundary Layer Control Methods Research Articles

Current state and future trends in boundary layer control on lifting surfaces

Successful flow control may bring numerous benefits, such as flow stabilization, flow reattachment, separation delay, drag reduction, lift increase, aerodynamic performance improvement, energy efficiency increase, shock delay or weakening, noise reduction, etc. For these purposes, many different flow control devices, which can be classified as passive, semi-active and active, have been designed and tested. This review paper aims to highlight the most promising and commonly employed boundary layer control methods as well as outline their potential in specific applications in aerospace and energy engineering. Referenced studies, performed on various geometries (flat plates, channels, airfoils, wings, blades, cylinders), are primarily numerical or experimental. Although enhanced aerodynamic performance is achieved in many cases, further research is required to draw general conclusions. This paper aims to demonstrate that, in the future, we may expect further developments of flow control actuators, as well as their increased application.

Моделювання течії в співвісному гвинтовентиляторі з управлінням примежовим шаром

The development and improvement of turboprop engines are one of the important tasks of modern aircraft engine building. Propeller performance significantly affects the overall efficiency of turboprop engines. An important issue is to increase the trust of the propeller or propfan. In this matter, promising energy methods for increasing lift deserve special attention. Energy methods for increasing the lift force are based on the use of additional energy from the power plant to improve the flow around the blade and increase its bearing properties. The purpose of this work is to assess the influence of the boundary layer control on the blades of a coaxial propfan on the thrust. A coaxial propfan was chosen as the object of research. The rotor fan consists of two rows of blades, the first row has eight blades, the second - six. The peripheral diameter of the blades of the propfan is the same and amounts to 4.5 m. The cruise mode of operation was selected for the study. Modeling the flow in a coaxial propfan was based on the solution of the Navier-Stokes system of equations, which was closed by the SST Gamma Theta Transition model of turbulent viscosity. The computational grid consisted of 20 million cells, type-block, structured and unstructured with an adaptation of the boundary layer. In this study, an active boundary layer control method was chosen. The boundary layer was controlled only on the blades of the first row of the propfan. In the peripheral region of the blade, an additional mass of air was blown out through the slot, at a distance of 70 % of the profile chord. Blowing out a thin jet near the blade wall to increase the flow energy serves as an effective means of controlling the flow separation and increasing the bearing capacity of the propfan blade. Analysis of the simulation of the flow in a propfan with control of the boundary layer showed that the addition of energy to the boundary layer contributes to the filling of the velocity profile in the boundary layer, leads to a decrease in resistance and an increase in the thrust of the propfan. The results of the study showed that for the studied scheme of blowing out an additional mass of air on the propeller blades, it is possible to increase the thrust force up to 100 N. In the future, it is planned to investigate other schemes for controlling the boundary layer to increase the thrust of the coaxial propfan.

Effects of the boundary layer control methods on stability and separation point

This paper concerns the benefits of the active boundary layer control methods. The main focus was studying the effectiveness of suction control for a laminar flow over an airfoil. However, injection normal to or along the wall was also approached using two numerical methods. For different values and distributions of the velocity control magnitude, a systematic comparison was done. Having the results of the laminar flow, a linear stability analysis based on the small disturbance theory was carried out obtaining both the neutral stability curves and the transition point. In the end, for each case, results were presented with the corresponding observations. Additionally, a study on the dependency of the separation point with respect to the injection velocity magnitude was done.

Advances in drag-reduction methods related with boundary layer control – A review

In our day to day life we see the phenomenon of turbulence everywhere, and it is one of the main reasons in loss of energy. We all know about the energy crisis our world is facing and the global warming problem planet earth is facing, so there is an urgent need to decrease our energy consumption and for that increasing efficiency is one of a key factor. One of the major part in turbulence is the viscous force that occurs between any two boundaries be it solid–liquid or solid–gas boundary. The friction force which occurs in turbulence greatly decreases the efficiency, so decreasing the friction forces can significantly improves the efficiency. In his paper boundary layer control methods which can help in drag reduction are reviewed. Methods such as polymer additives, super hydrophobic surfaces, air bubbles drag reduction, morphology drag reductions composite drag reductions were reviewed along with their applications in various fields is discussed. Finally some new ideas are presented to improve the current drag reduction techniques.

Boundary layer instability control in the unsteady cloud cavitating flow

In this article, we propose a passive boundary layer control method to control the vortex structure of the cavity on the suction side and wake region of the CAV2003 benchmark hydrofoil. This method may be used in different applications such as marine, turbomachinery and hydraulic machinery. First, we used a hybrid URANS model for turbulence to simulate the 3D unsteady cloud cavitating flow and validated it based on experimental data. We performed the numerical simulations using open source code OpenFOAM and an Euler-Euler cavitation model. Second, we studied the effect of passive boundary layer control method on vortex structure on the suction side of the hydrofoil and in wake region. We showed that this control method may influence the boundary layer structure on the hydrofoil surface and also near the trailing edge. Using this technique the pressure distribution and the fluctuating part of the velocity field on the hydrofoil surface were modified over the chord length. This method induced a stabilization of the boundary layer and delay its separation. Therefore a significant reduction in cavitation-induced vibration may be expected.

Testing a Special Shaped Body of Revolution Similar to Dolphins Trunk

Background. The high swimming velocities of some aquatic animals such as dolphins continue to attract great interest of researchers. The friction drag of the dolphin, estimated with the use of turbulent friction coefficient of the flat plate, was so high to declare that the dolphin should not be able to swim as fast as it does with the muscle power it possesses. Some previous tests of the rigid bodies, similar to the animal shapes, and gliding dolphins revealed the attached flow patterns. Nevertheless, the researchers connected with industrial applications believe that separation is inevitable on every smooth shape, provided no active boundary-layer control methods (e.g., suction) are applied.Objective. The aim of the paper is to test a special shaped rigid body of revolution in the wind tunnel in order to show that the boundary-layer separation can be removed without any active flow control methods.Methods. Wind tunnel tests were carried out at velocities 15, 35, and 55 m/s. Static pressure measurements and the oil-flow visualization were used. For this study, we take the UA-2 special shaped model of 200 mm length and 56.78 mm of the maximum diameter. The closed version of the UA-2c model is similar to the dolphin body. The tests were carried out in the subsonic wind tunnel MUB of the Institut für Strömungsmechanik (ISM) at Technische Universität Braunschweig, Germany. The wind tunnel MUB of ISM is an actively cooled Goettingen type tunnel with a square section of 1.3 m and the turbulence level of about 0.2 %. The technique of oil-flow visualization was used to deliver information of the surface near flow. The color used is a mixture of thin mineral oil and petrol, in an optimized ratio. The very fine titan-dioxide particles and UV-light reactive polymer particles in the color deliver a high contrast picture of the flow directions with a high spatial resolution.Results. The distribution of the static pressure and the oil-flow visualization are presented at three angles of attack. The flow pattern at zero angle of attack is probably attached and laminar.Conclusions. Pressure measurements and the flow visualization on the special shaped body of revolution showed that it is probably possible to avoid separation in rather large range of the Reynolds numbers. Further experiments are necessary with the use of a visualization of the flow volume and hot-wire velocity probes to clarify the behavior of the boundary layer, its separation and laminar-to-turbulent transition characteristics.

Effects of Boundary Layer Control Method on Hydrodynamic Characteristics and Tip Vortex Creation of a Hydrofoil

Abstract There is currently a significant focus on using boundary layer control (BLC) approach for controlling the flow around bodies, especially the foil sections. In marine engineering this is done with the hope of increasing the lift - to - drag ratio and efficiency of the hydrofoils. In this paper, effects of the method on hydrodynamic characteristics and tip vortex formation of a hydrofoil are studied. Steady water injection at the tip of the hydrofoil is simulated in different conditions by using ANSYS-CFX commercial software. Validity of the proposed simulations is verified by comparing the obtained results against available experimental data. Effects of the injection on the lift, drag, and lift - to - drag ratio are studied and the ranges within which the injection has the most positive or negative effects, are determined. Furthermore, flow pattern and pressure variation are studied upon the water injection to determine the most positive and negative case and to ascertain the main reasons triggering these phenomena.

AIRPLANE FRICTION DRAG REDUCTION BY MEANS OF MICROBLOWING THROUGH PERMEABLE WING SURFACE SECTIONS

The last 45 years have been characterized by escalation of the problem of energy saving and, accordingly, the search and implementation of various resource-saving technologies in various spheres of human activity and, first of all, in the energy and transport sectors. In particular, this problem became urgent for aviation transport and it is not difficult to assume that in the future this process will only increase. Gradual optimization of power plants and aerodynamic design of aircraft in the process of steady improvement of aircraft characteristics and development of the appropriate technological base led to the fact that the traditional methods of fuel consumption reducing are almost exhausted. Aircraft drag consists of several components: inductive, wave, pressure and frictional. The first three components are studied well enough and methods of their reduction are widely used on airplanes. Nevertheless, friction drag can be effectively reduced by boundary layer control methods. Among them there are wellknown and deeply studied ones but for some reasons they were not applied earlier because of the inability or ineffectiveness of their technological implementation. There are methods that are still awaiting for their detailed studies. Determining the optimal, in terms of the frictional drag reduction and the technological considerations, placement and length of the blowing section (or several sections) along the airplane wing chord are practically unexplored. This set of problems is the subject of authors consideration and research presented in this article. On the basis of An-124 aircraft wing the advantages and phenomena of the influence of micro-blowing through the porous section of streamlined surface have been investigated. Parametric analysis of the effect of blowing speed, location and length of the blowing section along the wing has been performed and the conditions and ratios of the parameters, which provide the best effect for the case of maintaining flow without separation, have been determined.

The effect of variable stator on performance of a highly loaded tandem axial flow compressor stage

Increasing the aerodynamic load on compressor blades helps to obtain a higher pressure ratio in lower rotational speeds. Considering the high aerodynamic load effects and structural concerns in the design process, it is possible to obtain higher pressure ratios compared to conventional compressors. However, it must be noted that imposing higher aerodynamic loads results in higher loss coefficients and deteriorates the overall performance. To avoid the loss increase, the boundary layer quality must be studied carefully over the blade suction surface. Employment of advanced shaped airfoils (like CDAs), slotted blades or other boundary layer control methods has helped the designers to use higher aerodynamic loads on compressor blades. Tandem cascade is a passive boundary layer control method, which is based on using the flow momentum to control the boundary layer on the suction surface and also to avoid the probable separation caused by higher aerodynamic loads. In fact, the front pressure side flow momentum helps to compensate the positive pressure gradient over the aft blade’s suction side. Also, in comparison to the single blade stators, tandem variable stators have more degrees of freedom, and this issue increases the possibility of finding enhanced conditions in the compressor off-design performance. In the current study, a 3D design procedure for an axial flow tandem compressor stage has been applied to design a highly loaded stage. Following, this design is numerically investigated using a CFD code and the stage characteristic map is reported. Also, the effect of various stator stagger angles on the compressor performance and especially on the compressor surge margin has been discussed. To validate the CFD method, another known compressor stage is presented and its performance is numerically investigated and the results are compared with available experimental results.

Boundary layer control in transonic compressor flows

This article presents a novel concept for coupled boundary layer control in transonic axial compressors. Proposed control scheme utilizes two steady active methods and couples them creating compact and in principle passive boundary layer control method. Both presented methods (steady suction and steady tangential blowing) are known since many years. In this article they are presented in the context of coupling them on two neighbouring stages. Presented analysis shows that the proposed solution allows for very high stage loadings and pressure ratios. The concept is presented on the set of transonic cascades, where it shows to prevent separation in regions of high adverse pressure gradients (associated both with occurrence of shockwaves and high aerodynamic loading).

고효율 LCD 감광막 제거기술 구현 연구

The realization of the photoresist(PR) removal method with vaporized water and ozone gas mixture has been studied for the LCD TFT array manufacturing. The developed PR stripper uses the water boundary layer control method based on the high concentration ozone production technology. We develop the prototype of PR stripper and experiment to find the optimal process parameter condition like as the ozone gas flow/concentration, process reaction time and thin boundary layer formation. As a results, we realize the LCD PR strip rate over the 0.4 <TEX>${\mu}m/min$</TEX> and this PR removal rate is more than 5 times higher than the conventional immersion type ozonized water process.

Passive Control of Plume Interference on Slender Axisymmetric Bodies

The physics of the plume-induced shock and separation, particularly at high plume to exit pressure ratios with and without shock-turbulent boundary-layer control methods, were studied using computational techniques. Mass-averaged Navier-Stokes equations with a two-equation turbulence model were solved by using a fully implicit finite volume scheme and time.marching algorithm. The control methodologies for shock interactions included a porous tail and a porous extension attached at the nozzle exit or trailing edge. The porous tail produced a weaker shock and fixed the shock position on the control surface. The effect of the porous extension on shock interactions was mainly to restrain the plume from strongly underexpanding during a change in flight conditions. These techniques could give an additional dimension to the design and control of supersonic missiles.

Control of plume interference effects on axisymmetric afterbodies

Plume interference effects on the axisymmetric flowfields around powered missiles are investigated using computational techniques. The study is mainly to understand the physics of the plume-induced shock and separation particularly at high plume to exit pressure ratios with and without shock-turbulent boundary layer control methods. Mass-averaged Navier-Stokes equations with the RNG k-ε turbulence model are solved using a fully implicit finite volume scheme and time-marching algorithm. The shock position and extent of separation was found to be dependent on the freestream Mach number and plume pressure ratio. Rounding the tail or a groove on the surface near the tail moved the shockwave downstream of the tail fin which should enhance the control of the missile.

Control of flow separation from leading edge of a shallow rectangular cylinder through momentum injection

Finding a method to suppress aeroelastic vibrations of a bridge deck is an important research to construct a superlong suspension bridge with the main span longer than 2000 m. For this end, the boundary-layer control method was proposed and a fundamental experimental research was conducted. This method was applied to the suppression of torsional flutter of a shallow rectangular prism which was one of typical fundamental configurations of a bridge deck section. The results obtained from measurements of surface pressure distributions and aeroelastic vibration responses showed that the proposed boundary-layer control method through momentum injection was effective for suppressing the torsional flutter of a shallow rectangular prism.

Study on the Prevension of the Intrusion of Saline Wedge

From engineering aspects, the techniques for the prevention of the intrusion of salhie wedge are quite important. This paper proposed boundary layer control method using barrier settled on the river bed to reduce the length of the saline wedge. Various type of barriers were tested their effectiveness.Theoretical and experimental study were conducted on the critical intrusion length of the saline wedge due to the barrier. Both results were compared and revealed good comparison. Eaves effect which attached downstream side of the barrier to control the motion of lower layer was also studied and found its effectiveness.

急速非定常熱伝達と伝熱制御

Rapid transient heat transfer of milli- or micro-second order has come to play an important role in advanced engineering, and the demand for active and direct control technology of heat transfer is growing. In this article, the recent needs for rapid transient heat transfer and its control are considered, and the conceptual differences between heat-transfer control and conventional temperature or thermal control is discussed. Then, the methods of heat-tranfer control are divided into passive and active methods. Active methods such as the variable physical property method, external-force method, boundary-layer control method, and phase change method are reviewed.

Active control of super-tall structure vibrations under wind action by a boundary-layer control method

The authors have been developing active control methods for suppressing the aerodynamic vibrations of super-tall structures, like pylons of super-long bridges and super-tall buildings, which will be constructed in the next century. Boundary-layer control by rotating cylinders at the leading edge is treated as an active control method for suppressing aerodynamic vibrations. Previous wind tunnel tests conducted by using a two-dimensional square prism gave good results for suppression of the aerodynamic response due to vortex-excited vibration and galloping. On the basis of the two-dimensional wind tunnel test results, three dimensional wind tunnel tests were conducted. The experimental results had a relatively good agreement between two and three dimensional tests.

急速非定常伝熱と伝熱制御

Rapid transient heat transfer of milli- or micro-second order has come to play an important role in advanced engineering, and the demand for active and direct control technology of heat transfer is growing. In this article, the recent needs for rapid transient heat transfer and its control are considered, and the conceptual differences between heat-transfer control and conventional temperature or thermal control is discussed. Then, the methods of heat-tranfer control are divided into passive and active methods. Active methods such as the variable physical property method, external-force method, boundary-layer control method, and phase change method are reviewed.

Heat-Transfer Control: Principal Focus on Japanese Research

Rapid transient heat transfer of milli- or micro-second order has come to play an important role in advanced engineering and technology, and the demand for active and direct control of heat transfer is growing. In this article, first, the recent needs for heat-transfer control are considered in detail. Then, the difference in concept between heat-transfer control and conventional temperature or thermal control is discussed. In the following sections, the methods of heat-transfer control are divided into passive and active methods, and the active control methods are classified into eight categories: transient heat-transfer method, molecular dynamics method, variable physical property method, external-force control method, boundary-layer control method, phase change method, multiphase media method, and porous media method. With respect to each of them, the controllability of heat transfer and its feasibility are discussed, quoting principally the recent Japanese literature. In the concluding remarks, the future trends of heat-transfer control are described.

The Effect of a Slat on Boundary Layer Characteristics and Cavitation of the Main Foil

It is known that the cavitation is dependent upon the boundary layer characteristics. Therefore, it is considered that cavitation can be controlled by controlling the boundary layer.This paper deals with a SLAT-FOIL combination, main foil and upstream slat. The slat is one of the boundary layer control methods for foil sections.Firstly, the authors designed the SLAT-FOILs to increase the pressure at the laminar separation point as high as possible, and verified the cavitation suppression effect by cavitation tunnel tests.Secondly, the authors studied the interaction between the wake of the slat and the boundary layer on the main foil, and found that when the wake of the slat merged into the boundary layer on the main foil, it accelerated turbulent transition. If the pressure of the turbulent transition point was high enough, the cavitation was remarkably suppressed.In conclusion, two methods of the cavitation control (suppression) can be suggested, those are as follows.1. A slat can change the pressure distribution on the foil. As the result of increase of the pressure at the laminar separation point, the incipient cavitation number of sheet type cavitation can be decreased.2. When a slat is near the foil, the wake of the slat is mixed into the boundary layer on the main foil, which accelerates turbulent transition. If the pressure on the transition point is high enough, the incipient cavitation number is remarkably decreased.