Top PDF Energization of Boundary Layer Over Wing Surface By Vortex Generators

[3] B. Raghava Rao, Rangineni Sahitya [3]: Focuses on the effect of stall angle on the performance of the wing .here performance parameters include lift, drag co-efficient and pressure distribution of two dimensional subsonic stream over a symmetric airfoil at different angle of attacks and at low and high Reynolds number. So, in order to perform this experimental test was conducted in low speed wind tunnel, and the computational analysis was performed using ANSYS- 15(FLUENT) software

(or airfoil, such as an aircraft wing) or a rotor blade of a wind turbine. VGs may also be attached to some part of an aerodynamic vehicle such as an aircraft fuselage or a car. When the airfoil or the body is in motion relative to the air, the VG creates a vortex, which, by removing some part of the slow-moving boundary layer in contact with the airfoil surface, delays local flow separation and aerodynamic stalling, thereby improving the effectiveness of wings and control surfaces, such as flaps, elevators, ailerons, and rudders.

suppress/enhance turbulence or prevent/provoke separation, drag reduction, lift enhancement. It also increases the angle of stall by delaying the flow separation. Stalling is the strong phenomena during landing because at the time of landing aircraft high angle of attack leads to stalling of aircraft. This stall makes uncontrolled, leads to accident. To avoid this kind of situation we need to increase the stalling angle. Hence improved stalling characteristic is the best way to ease landing complexity. After passing the critical angle of attack, wing is unable to produce sufficient lift to balance weight, if this angle exceeds it leads to flow separation, thereby increase in drag, which reduces the L/D ratio. Modifying the aircraft wing structure by means of placing dimple will reduce the drag to considerable amount and helps to stabilize the aircraft during stall. For example, a golf ball with a dimpled surface can travel higher and further than a smooth surfaced golf ball when subjected to identical force. The dimples on golf balls induce turbulence at lower Reynolds number, providing extra momentum or energy to the boundary layer and causing delay in flow separation. This phenomenon causes smaller wake areas or swirling flow regions behind the ball, thus reducing the total drag. In deep, dimples delay the flow separation point by creating turbulent boundary layer by reenergizing potential energy in to kinetic energy.

Eibeck and Eaton [4] studied the structure of the longitude vortex created by the delta winglet at different downstream locations in 1987. Their work showed that the longitude vortex can thicken the otherwise flat surface boundary layer. The typical detailed structure of the longitude vortex caused by the delta winglet on the flat surface boundary layer has been detected by Wu et al. [5]. According to their study, the longitudinal main vortex and the induced vortex can be observed downstream of the winglet. The flow can be divided into two regions, inflow and outflow. They then discovered that an increase in aspect ratio can move the vortex toward to the surface and decrease the turbulent intensity of the flow downstream [6]. The escalation of turbulence fluctuation seems to revert more when the attack angle of the delta winglet increases [7]. The increase of attack angle of the delta winglet can also strengthen the intensity of the swirling motion in a circular tube [8], though it can decrease the vorticity of the longitude vortex for the flat surface case [7].

Abstract: The aerodynamic efficiency of a NACA 0012 AR 4 wing was affected through periodic contours aligned in the flow direction resembling a “wrinkled” texture. Streamwise and cross-stream Particle Image Velocimetry (PIV) were conducted at the University of Dayton Low Speed Wind Tunnel (UD-LSWT) around Reynolds number of 135,000 on the NACA 0012 AR 4 wing with and without surface contours. Wings with 6 contour sections was designed by spline fitting two NACA 0012 airfoil profiles in the spanwise direction. Both 2D (wall-to-wall model) configuration and 3D configuration of the wings were tested to determine the effects of surface contours on the parasite and induced drag of the wing. Streamwise PIV results indicated an increase in momentum deficit in the wake of the mid-contour region due to enhanced boundary layer separation from the upper surface of the mid-contour region. The cross-stream PIV results indicated a decrease in the magnitude of azimuthal velocity, circulation and RMS quantities in the wingtip vortex with the surface contours. The reduction in the wingtip vortex properties indicates that the contours were effective in blocking the spanwise flow feeding into the wingtip vortex on the surface of the wing. Keywords: Aerodynamic Efficiency; Wrinkled/Contoured Surface; Surface Flow

VII. G EOMETRY OF V ORTEX G ENERATOR In connection with the size, the thickness of the boundary layer is measured based on the assumption that the optimum height of the VG would be almost equal to the boundary layer thickness. The boundary layer thickness at the roof end immediately in front of the separation point is about 30 mm. As to the location of VGs, a point immediately upstream of the flow separation point was assumed to be optimum. The effects of half-delta wing VGs mounted at this point are presented. Consequently, the optimum height for the VG is estimated to be up to approximately 3ated to be up to approximately 20 mm. As to the shape, a bump-shaped piece with a rear slope angle of 10°-20° is selected.

depicted in figure(12). It can be seen that the thermal enhancement ratio significantly increases with presence of vortex generators as compared with plane channel. This increase is noticed for any specified Reynolds number. For each vortex generator, it is decreased as Reynolds number increase . The introduction of VGs generates the longitudinal vortices and secondary flow, which breaks the boundary layer development. The boundary layer is thinner and the heat transfer is enhanced.As fact, the disturbing and mixing of flow would change the original field of flow and temperature and the flow separation point and the recirculation zone are delayed for the streamlined configuration. The higher area ratio of the winglet vortex generators greats more disturbance of the boundary layer and provides a better air flow mixing. Hence, the heat transfer is enhanced. The heat transfer enhancement from the rectangular vortex generator was significant more than those of other shapes vortex generators. The optimum increase is formed at an angle of attack (ß=45°). The thermal enhancement ratio varied from 1.6 to 2.8 with Re increasing. The reason of the above difference is described as follows. The winglet vortex generators make a hindrance in the main flow stream with a pressure difference in upstream and downstream of the vortex generators. This mechanism creates a strong longitudinal vortices. These vortices extend for a large distance behind the winglet vortex generators and vanish slowly in stream wise flow direction .This flow interaction accelerating the mixing process between the cold and hot fluid and thus increasing the thermal enhancement ratio. The optimum enhancement ratio is pointed at the rectangular vortex generators while the minimum at parabolic vortex generators. This trend is founded for all tested sizes of vortex generators, however increasing the vortex generator size (represented here by A r ) leads to increase the

The second objective is to identify boundary layer thickness over the flat plate. The purpose is having MVGs placed within the boundary layer otherwise it would be ineffective. In order to measure the boundary layer thickness, it is required to measure the dynamic pressure from the surface upwards, either by using a transverse method or using wake rake. By applying the Bernoulli theory [1], the velocity change moving from the surface upwards can be measured. Starting from zero velocity on the surface (no slip condition theory) the velocity gradually increases up till reaching the free stream velocity. By measuring the point from zero velocity (surface) to the point after which velocity reaches freestream velocity the boundary layer thickness is measured.

The separated case of ISWBLI has been widely adopted to test the separation control effects of MVG. Babinsky et al. [4] performed an important experimental study, which later becomes the datum for subsequent numerical studies. The experiment was carried out in the supersonic wind tunnel operating at Ma=2.5. The boundary layer (δ≈6 mm) that develops over the wind tunnel floor was used to interact with the shock wave generated by a 7° wedge. Two geometrically similar micro ramps with heights of 3 mm and 6 mm (h/δ=0.5, 1.0) were installed and they were placed in both single and array arrangements respectively. The control effects were evaluated through oil flow visualization (see figure 24(a)) and surface static pressure variation across the interaction region. Velocity profiles were also studied at various streamwise and spanwise positions such that the three dimensional effects could be evaluated.

161 Effects of Boundary Layer and Tip Geometry Vortex lines of opposite sign annihilate each other Vortex lines coming from the wing surface boundary layer Rectangular Tip Case Vortex li[r]

A theoretical study is presented of three-dimensional turbulent flow provoked in a boundary layer by an array of low-profile vortex generators (VGs) on the surface.. The typ[r]

Abstract: The present investigation provides an insight in the steady, incompressible and electrically conducting boundary layer flow of viscoelastic nanofluid flowing due to a moving, linearly stretched surface. The governing system of nonlinear partial differential equations is simplified by considering Boussinesq and boundary layer approximations. An analytical solution of the resulting nonlinear ordinary differential equations for momentum, energy and concentration profiles is obtained using the homotopy analysis method (HAM).

The flow field was measured for various free-stream wind speeds for all setups and both measurement methods. Seven investigated free-stream velocities was in the range from 5 m/s to 23 m/s which corresponds to Reynolds number Re from 18 000 to 180 000 (based on the boundary layer depth δ and the free stream velocity U δ ), or Re* from 1 to 276 (based on roughness length z 0

over moving or stretching surfaces included the work of Abdelhafez [7] and Chappidi and Gunnerson [8] who independently considered flows over moving surfaces in which both the surface and the free stream moved in the same direction. In their studies, they formulated two sets of boundary value problems for the cases U   U  and

buoyancy effects caused by diffusion of heat and chemical species. The study of such processes is useful for improving a number of chemical technologies, such as polymer production and food processing. In nature the presence of pure air or water is impossible. Some foreign mass may be present either naturally or mixed with air or water. The present trend in the field of chemical reaction with viscosity analysis is to give a mathematical model for the system to predict the reactor performance. A large amount of research work has been reported in this field. In particular, the study of chemical reaction, heat and mass transfer with heat radiation is of considerable importance in chemical and hydrometallurgical industries. Chemical reaction can be codified as either heterogeneous or homogeneous processes. This depends on whether they occur at an interface or as a single phase volume reaction. Anjalidevi and Kandasamy (1999) considered the chemical reaction between species A and B to be of first order, homogenous and with a constant rate. Ibrahim and Makind (2011) examined chemically reacting MHD boundary layer flow of heat and mass transfer past a low- heat-resistant sheet moving vertically downwards in a viscous electrically conducting fluid permeated by a uniform transverse magnetic field. Adeniyan and Adigun (2012) examined the effects of a chemical reaction on stagnation point MHD flow over a vertical plate with convective boundary conditions but neglected the energy due to pressure force. Muthucumaraswamy et al. (2006) studied study of chemical reaction effects on vertical plate with variable temperature. Unsteady free convection flow past a vertical plate with chemical reaction under different temperature condition on the plate is elucidated by Bhaben Ch

Vortex/wave interaction, for the flow in a boundary layer, pipe or channel, for example, concerns the nonlinear interplay between the mean vortex part, comprising longitudinal or streamw[r]

, 10 4 and 10 5 , and three values of vortex circulation, in negative and positive cases. The pressure gradient induced by the vortex convection generates, through the Lighthill’s mechanism, a vorticity flux at the wall during the interaction. Inside the boundary layer, according to the sign of the vortex, a rolling phenomenon is observed, with an effect of wave upstream or downstream. The vortex has upward or downward trajectory depending on its sign. For a strong negative vortex, a recirculation zone and a bubble of vorticity are created. A secondary structure is then generated, with opposite vorticity, and ejected out of the boundary layer. The vortex then bounds.

The second configuration of delta wings also produced a 14% increase in the mean air turbulence intensity measure of the time-variability in air speed and reduced the variability of evap[r]

The obtained third-order, nonlinear, ordinary differential equation cannot be solved analytically and has to be solved numerically. A technique that can be used is the Runge-Kutta method. The method integrates in small steps along the y-direction, starting from the wall. However, because we only have two of the boundary conditions at y=0 (the boundary condition for f 00 (0) is missing), we have to assume a value for this boundary condition and check if at large η, the condition f 0 (∞) = 1 is satisfied. This process is repeated until the solution is congruent. This method is also called the ’shooting-method’ and Matlab will provide the help needed to find the solution.

At higher operating temperature, the effects of thermal radiation and heat transfer play a pivotal role on the fluid flow problem of boundary layer. The application of controlled heat transfer in polymer industries is very important to get final product of desired parameters. The modern system of electric power generation, plasma, space vehicles, astrophysical flows and cooling of nuclear reactors are governed by applications of thermal radi- ation and heat transfer of fluid flow. Elbashbeshy [21] determined the effect of radiation on flow of an incom- pressible fluid along a heated horizontal stretching sheet. Sajid and Hayat [22] extended this concept by investi- gating the influence of thermal radiation on the boundary layer flow over an exponentially stretching sheet and solved the problem analytically. Recently, Bidin and Nazar [23], Jat and Chaudhary [24], Nadeem et al. [25] and Mukhopadhyay and Gorla [26] investigated various aspects of such problem either analytically or numerically.