Mohammad Mashud, Associate Professor, Department of Mechanical Engineering, Khulna University of Engineering and Technology (KUET). 37 Figure 5.1(b) Flow around a symmetrical airfoil mounted in a steady flow 38 Figure 5.1(c) Flow around a circular arc airfoil mounted in a steady flow 38 Figure 5.1(d) Flow around a mounted airfoil General Joukowsky.
General
The purpose of this investigation is to study the effect of surface suction and injection on flow control over a specific airfoil. The case studied is the flow field over a subsonic airfoil with suction and injection slots.
Objectives of the Research Work
Motion of the solid wall
Slit Suction
Tangential blowing and suction
Continuous suction and blowing
The stability of the boundary layer and the transition to turbulence are also significantly influenced by continuous sucking and blowing.
Using Vodei Generator Jets
Pulse Jet
Acoustically Active Surfaces
To develop a mechanically simple and robust actuator for active flow separation control on axial compressor vanes, three different types of acoustic transducers were tested in a wind tunnel. Since it could not focus the disturbances over a small area, the acoustosurf was developed next.
Synthetic jet
It consisted of an array of flush-mounted narrow strip acoustic transducers that could detect surface pressure fluctuations prior to separation. The acoustosurf is believed to produce a synergistic interaction between roughness, surface flexibility and acoustic radiation to redirect the kinetic energy of the flow by exploiting flow instabilities.
LITERATURE REVIEW
Flow Phenomena
- Laminar flow
On an aircraft wing, the boundary layer is the part of the flow near the wing. The boundary layer is a very thin sheet of air that extends over the surface of the wing (and all other surfaces of the airplane).
Turbulent flow
- Compressible Flow
- Incompressible Flow
- Couette Flow
- Secondary Flow
- Active Control
- Reactive Feedback Control
However, by making the 'incompressible' assumption, one can greatly simplify the equations governing the flow of the material. These regions are usually in the vicinity of the boundary of the liquid adjacent to solid surfaces where viscous forces are at work, such as in the boundary layer. Heating and cooling of the surface can affect the flow through the resulting viscosity and density gradients.
Predetermined control includes the use of constant or unsteady energy input without regard to the particular state of the flow. For example, the presence of friction in the flow causes a shear stress at the surface of the body, which in turn contributes to. Adaptive schemes attempt to develop models and controllers via some learning algorithm without regard to the details of the flow physics.
The identification of the system is carried out independently of the flow dynamics or the Navier-Stokes equations governing these dynamics. Finally, optimal control theory applied directly to the Navier-Stokes equations can be used to minimize a cost function in the control space. The subsequent application of sub-optimal control theory to a numerically simulated turbulent channel flow is reported by Moin and Bewley [8].
Wall-Bounded and Free-Shear Flows
- Inviscid and Viscous Instabilities
- Regimes of Reynolds and Mach Numbers
- Convective and Absolute Instabilities
- Classical Control Tools
Examples of such control include changing the exit geometry of the jet from circular to elliptical [17], using periodic suction/injection on the underside of an open body to influence its wake (Williams and Amato, 1989 ) and the vibration of the separator plate. of a mixing layer [18]. Due to their unsteady nature, free shear flows undergo transition at extremely low Reynolds numbers compared to wall-bounded flows. These are usually velocity profile modifiers, for example back pressure gradient, injection, cooling (in water) and heating (in air), which reduce the completeness of the profile with increased risk of transition and premature separation.
The goal is of course to keep this fine below the potential savings; that is, the net drag will be higher than that of the flat-plate laminar boundary layer, but probably well below the viscous drag in the flat-plate turbulent flow. If any of the growing disturbances has a group velocity of zero, the flow is absolutely unstable. In this case, some of the growing disturbances can travel upstream and continuously disrupt the flow even after the initial disturbance has been neutralized.
Although well established in the laboratory and successfully tested in the field, the routine application in the field of the variety of available LFC strategies is awaiting the removal of several technological obstacles related mainly to cost, maintenance and reliability issues [24, 25, and 261 .The first two give only a modest reduction in drag of the order of 10%, while the polymer additives result in a significant reduction of up to 80%. In fact, many of the remaining gains to be made in aerodynamics appear to involve various types of flow control, including split flow control.
Conclusions
Future possibilities for the application of flow separation control in aviation include providing structurally efficient alternatives to flaps or slats; using cruise on conventional aircraft to take off and land on thick-span loader wings; as well as the use of cruise in high-speed civilian transport for beneficial reduction in wave disturbance drag, increased leading edge thrust, and improved hull and upper surface lift. Typical, and in some cases serious, problems associated with current separation control include parasitic device resistance or power consumption; weight, volume, complexity, reliability or cost of the system; sensitivity of the action to the posture or orientation of the body;.
METHODOLOGY
Wind Tunnel
Closed loop wind tunnels are advantageous over open loop wind tunnels for the following reasons: Flow quality can be easily controlled with screens and corner bends; less energy is required to create an air flow of a given size and velocity; the wind tunnel runs more quietly. By changing the drive motor's power supply, the tunnel speed can be varied. The tunnel-free flow rate is achieved by a pitot tube mounted in the middle of the wind tunnel, which is connected to the digital electronic manometer model METRAVI PM-01 NEDA 1604 IEC 6F22 that would give a reading of the static pressure.
The electronic pressure gauge has a range of 0-100 bar with an accuracy of 0.05% of the pressure reading and a full scale resolution of 0.001%. This difference in speed results in a pressure difference between the top and bottom of the wing, which exerts a net upward force on the wing. The amount of lift obtained by a wing depends on the shape of its airfoil and its angle of attack.
There is usually a relationship between the angle at which the wing is permanently inclined to the aircraft's longitudinal axis and the amount of lift generated. The secondary liquid injected and sucked through a tube connects buster head and head pipe of the four slots or holes. The width of each slot is 1 mm and diameter of the holes is 1 mm and the slots and holes are 30 mm apart.
Experimental Setup
- Pressure Measurement
For pressure measurement, a digital manometer was placed outside the wind tunnel test section. At every 10 mm distance of the model, holes were drilled vertically and vinyl tubes were placed in these holes. The surface pressure values of the model were measured in accordance with different values of wind tunnel speed, angle of attack and frequency.
During the experiment, the test airfoil was installed in the middle of the test section. The reason for this state of affairs is that the flow field around a wing is extremely complicated. When studying the flow around an airfoil, it is best to start with the simplest case, a flat plate.
After understanding this case, it is possible to slowly work up the shape resembling a general airfoil by gradually changing the shape of the flat plate and examining the flow around the body at each step of the change. However, this theoretical prediction is not observed experimentally, probably due to the viscous effects neglected in the inviscid theory. The effect of introducing circular bow camber into the airfoil of the flat plate is to decrease the angle of zero lift, i.e. L = 0 for a = -2k/c.
Results and Discussion .1 Pressure Distribution
The experiment was conducted to observe the change in the pressure coefficient of the upper surface of the airfoil in different angles of attack (a) and frequency (F) of suction and injection. And the pressure coefficient (Cr) remained almost constant up to the trailing edge of the airfoil as the x/c progressed. Here the maximum absolute value of the pressure coefficient on the upper surface of the airfoil increases to 1.5.
The angle of attack increasing to 12 degrees, the measured surface pressure coefficient distributions given in Figs. 5.2 (g) found that a separation bubble would be generated on the upper surface of the airfoil at x/c z 0.10 0.20. Here, the maximum absolute value of the pressure coefficient on the upper surface of the airfoil rises up to 1.86 at x/c = 0.1. The angle of attack increasing to 12 degrees, the measured surface pressure coefficient distributions given in Figs. 5.2 (h) showed that a separation bubble would be generated on the upper surface of the airfoil at x/c.
Here the maximum absolute value of the pressure coefficient on the upper surface of the airfoil increases to 2.18. The unfavorable pressure gradient across the upper surface of the airfoil would become larger and larger as the angle of attack increases. The airfoil drag coefficient was also found to increase slightly with increasing angle of attack.
CONCLUSIONS 6.0 Conclusions
Recommendations
W., "Numerical Study of Suction-Blowing Flow Control Technology for an Airfoil", Journal of aircraft, Vol. American Institute of Aeronautics and Astronautics, Washington, DC. editors) (1990). Viscous drag reduction in boundary layers, Progress in Astronautics and Aeronautics, vol. 123, American Institute of Aeronautics and Astronautics, Washington, D.C. An experimental investigation towards active control of turbulent boundary layers.
1993) "Feedback Control for Unsteady Flow and its Application to the Stokastic Burgers Equation," J Control of Plane Mixing Layer: Some Novel Experiments," i Current Trends in Turbulence Research, eds. Activities on Drag Reduction"Proceedings of the Seventeenth Congress of International Council of the Aeronautical Sciences, vol. ICAS-90-3.6.1, American Institute of Aeronautics and Astronautics, Washington, D.C. Supersonisk laminær flowkontrol på kommercielle transporter. redaktører) (1992) Natural Laminar Flow and Laminar Flow Control, Springer-Verlag, New York Controlled Leading-Edge Suction for the Management of Unsteady Separation over Pitching Airfoils,".
Discover "Control of flow separation and transition point above an airfoil at low re-number using simultaneous blowing and suction" AIAA Journal, Vol.44, no.
