Terry Ng

A Smart Wind Turbine Blade Using Distributed Plasma Actuators for Improved Performance

This paper presents an innovative Plasma Aerodynamic Control E! ectors (PACE) concept for improved performance of wind turbines. The concept is aimed towards the design of “smart” wind turbine blades with integrated sensor-actuator-controller modules to improve the performance of wind turbines. The system will be designed to enhance energy capture, and reduce aerodynamic loading and noise by way of virtual aerodynamic shaping. Virtual shaping is the modification of the flow field around the surface by means of flow control (plasma actuators), which results in flow changes as if the geometry itself is altered. In e! ect the flow control scheme is giving the designer the capability to change the e! ective pitch distribution across the turbine blade as needed to control blade loading. The present concept is based on the use of surface-mountable, single dielectric barrier discharge (SDBD) plasma actuators on the turbine blades for increased energy capture and noise reduction. The system will allow continuous operation of wind turbines at near optimal conditions (as close as possible to the rated power coe cient) using a smart/adaptive PACE system in both steady and unsteady conditions (wind gusts, varying wind speeds, etc.), thereby ensuring safety and optimal power capture for electricity conversion. Experimental data and computational model results are presented that show the feasibility of using plasma flow actuators to control the aerodynamic characteristics of selected wind turbine airfoil sections. Two airfoil profiles designed for wind turbine applications were selected for this study. These were the S827 and the S822 profiles. The S827 airfoil was used to examine circulation control to increase the e! ective camber, and leading-edge separation control to increase Clmax. The S822 airfoil was used to demonstrate geometric changes that promote local flow separations that can be manipulated by plasma actuators to control lift. Both these approaches produced controlled changes in the lift coe cients on the airfoils that were equivalent to a trailing-edge flap or a leading-edge slat, but without conventional moving surfaces.

Modification of the Flow Structure over a UAV Wing for Roll Control

Plasma enhanced aerodynamics was used to provide roll control at high angles of attack on a scaled 1303 UAV configuration. The 1303 planform has a 47 degree leading-edge sweep angle. The flow over the a half-span model was documented with dye flow visualization in a water tunnel for a range of angles of attack. This revealed a complex flow structure that varied with angle of attack. A half-span model with Single Dielectric Barrier Discharge (SDBD) plasma actuators was then tested in a wind tunnel. The model was mounted on a 2-D force balance designed to measure lift and drag. At larger angles of attack from 10 to 35 degrees, plasma actuators placed just below the leading edge were found to augment the lift. This configuration was implemented in a full-span model that was mounted on a sting that allowed free-to-roll motion. The ability of the plasma actuator arrangement to produce roll maneuvers was then investigated for a range of angles of attack and freestream speeds. The results indicated excellent roll control with roll moment coefficients that are comparable to conventional moving surfaces.

Yaw Control of a Blunt-Nose Projectile at High Angles of Attack Using Strakes

An experimental study was conducted to investigate the effects of different aftbody strakes on a projectile with a blunt-nose and a fineness ratio of 4. The effect of strake parameters such as shape, locations (axial and azimuthal), deployment height, and in some cases, the number of strakes implemented was examined. The main objective for the study is to identify promising strake configurations for effective yaw stabilization and control, and to identify changes in the effect of actuator parameters as a function of angle of attack. Wind tunnel experiments were conducted for angles of attack ranging from 0 to 64 deg at a Reynolds number of 0.19 x 10 6 and Mach 0.1. A few test cases were conducted to examine the effect of sideslip angles. The optimum azimuthal location for a strake was found to be the left and right side meridians and 1-inch (x/L = 0.083) from the nose apex. Large yaw control authority was attained for α > 40 deg. The largest yaw control authority was produced by a rectangular-shaped strake. The yaw control attained with this strake was close to symmetric with the strake placed at the corresponding left and right side meridians, and produced a side force and yawing moment to the opposite side of where it was mounted. Aftbody strakes were effective even at sideslip conditions and with larger fins.

A CFD Study of a Missile Aero Control Fin by Near-Wall Flow Modifications

A computational effort to obtain estimates of missile steering control authority at both low and high speeds using near-wall flow modifications on novel aerodynamic tail fins has been initiated. Numerical simulations on a swept threedimensional missile tail fin at low alpha, Mach 0.2 and Mach 2.0 are performed using a structured multi-zone compressible Navier-Stokes flow solver WIND. Two types of actuator boundary conditions are imposed via porous skin/small holes, located strategically on the surface of the missile aero control fin. These represent Reconfigurable Porous Technology “RePorT” enabling zero-net mass flow transpiration, and a hybrid system of suction and blowing. It is found that a more sophisticated boundary condition to simulate “RePorT” control scheme within WIND is needed in order to make meaningful comparisons with the existing low-speed wind tunnel data. Preliminary results are presented from the low-subsonic speed simulations using the suction and blowing boundary conditions on the tail-fin show pressure recovery and drag reduction effects at low angles of attack. High-speed baseline simulations at Mach 2.0 provide a clear identification of shock wave and boundary layer at regimes of interest for the targeted missile application.

Trajectory Control of a Small Caliber Projectile Using Active Transpiration

A method to generate aerodynamic control forces for steering a small caliber projectile using flow transpiration channels on a boattailed afterbody is numerically investigated. Steady state simulations are conducted at Mach 2 from 0 to 10 deg angles of attack with zero sideslip angle using Reynolds Averaged Navier-Stokes equations and Reynolds Stress turbulence model. Results show that the interaction of the jet exiting from the transpiration channels with the main stream flow results in a complex three-dimensional shock wave structure on the projectile base yielding coherent vortex structures downstream of the primary interaction shock. The asymmetry induced in the flow due to three-dimensional coherent structures generated by natural flow transpiration near the projectile surface results in a considerable force which can be used for steering a small caliber projectile.