Circulation Controlled Airfoil Analysis Through 360 Degrees Angle of Attack

Abstract

Wind turbines are a source of renewable energy with an endless supply. The most efficient types of wind turbines operate by utilizing the lift force of its blades to create a rotational force. The power capabilities of a wind turbine are tied to the blades’ ability to convert the aerodynamic forces into rotational energy. Vertical axis wind turbines (VAWT), unlike the more common horizontal axis (HAWT) type, do not need to be directed into the wind and can place the transmission and electrical power generation components at the bottom of the turbine shaft, near the ground. Currently VAWTs cannot feather or pitch the blades, in the same fashion as a HAWT, for a lift change to control power generation and/or rotational speed at different or changing wind speeds. A method of increasing the lift of a blade without physically moving the blade is to use circulation control (CC), via a blowing slot over a rounded trailing edge. The CC air flow entrains the air around the blade to create more lift. Adding an actuated valve for the blowing slot allows a CC-VAWT to control the amount of lift generated, as well as the location of the augmentation relative to the wind direction, resulting in augmented power generation. In order to study the performance capabilities of a CC-VAWT, a NACA0018 blade was modified to incorporate circulation control. This modified shape was analyzed using computational fluid dynamics at two Reynolds numbers and a wide range of angles of attack. The lift to drag ratio of the CC-VAWT blade shows benefits at low Reynolds numbers over a NACA0018 blade for post stall angles of attack, but there is a decrease in the lift to drag before stall due to a significant increase in drag of the circulation control models. Further CFD refinement and experimental investigations are recommended to validate the predicted effects circulation control will have on the performance of a VAWT.

Aerodynamic and aeroacoustic performance assessment of a vertical axis wind turbine by synergistic effect of blowing and suction

“…It should be noted that CC, unlike JF, improves lift mainly by changing the stagnant streamline movement and increasing circulation around the blunt body. 5 The principle of the circulation control and its application Graham et al [39] modified the NACA0018 airfoil shape to achieve the CC control, then numerically investigated the CC effects over two Reynolds numbers and a wide range of AOA. Constant CC control leads to a decrease in LDR before the occurrence of a stall, which may deteriorate the performance of the VAWT.…”

Dynamic Circulation Control for a Vertical Axis Wind Turbine using Virtual Solidity Matching

“…Interest was lost as other energy technologies outpaced development of the VAWT, but renewed investigations in the effort picked up at WVU in 2008 due to availability of pneumatic values that could be located within the blade. Recently, the concept of using CC to augment lift for increased energy capture was overviewed by Smith [25] and a blade shape and internal pneumatic design was investigated by Graham and Panther [15] [26]. The combination of CC and a VAWT that contains a valving system with upper and lower trailing edge jets has become known as the CC-VAWT within the current effort.…”