2-D Circulation Control Airfoil Benchmark Experiments Intended for CFD Code Validation

Abstract

A current NASA Research Announcement (NRA) project being conducted by Georgia Tech Research Institute (GTRI) personnel and NASA collaborators includes the development of Circulation Control (CC) blown airfoils to improve subsonic aircraft high-lift and cruise performance. The emphasis of this program is the development of CC active flow control concepts for both high-lift augmentation, drag control, and cruise efficiency. A collaboration in this project includes work by NASA research engineers, whereas CFD validation and flow physics experimental research are part of NASA's systematic approach to developing design and optimization tools for CC applications to fixed-wing aircraft. The design space for CESTOL type aircraft is focusing on geometries that depend on advanced flow control technologies that include Circulation Control aerodynamics. The ability to consistently predict advanced aircraft performance requires improvements in design tools to include these advanced concepts. Validation of these tools will be based on experimental methods applied to complex flows that go beyond conventional aircraft modeling techniques. This paper focuses on recent/ongoing benchmark high-lift experiments and CFD efforts intended to provide 2-D CFD validation data sets related to NASA's Cruise Efficient Short Take Off and Landing (CESTOL) study. Both the experimental data and related CFD predictions are discussed.

Application of Circulation Controlled Blades for Vertical Axis Wind Turbines

“…For this relatively simple comparison a torque contribution is calculated for the mid-span blade element of a H-rotor VAWT using Equations (1)-(3) and the measured lift and drag characteristics, and neglects the momentum and tip losses and dynamic effects included in the DMST model. Since the variation of drag with AoA was not reported in [33], it is assumed that the CC-E0020EJ aerofoil experiences the same drag increase with AoA as the NACA0018 aerofoil, as given in Equation (7):…”

“…To eliminate low Reynolds number characteristics, such as laminar separations, the wind tunnel velocity was increased until a constant baseline drag was achieved. Using this criteria, measurements were obtained for a tunnel dynamic pressure of 718 Pa corresponding to a chord Reynolds number, R c = 0.5 M. These measurements are described in detail in [33] and have been used to evaluate the CFD procedure used in this study.…”

“…The 20% thick section has a 0.22 m chord, with nozzle heights that could vary from 0.1%c to 0.5%c, and is shown in Figure 4 compared with the NACA0018 section (scaled to a unit chord). The aerofoil was jointly tested in the Basic Aerodynamic Research Tunnel at NASA Langley as well as the Model Test Facility at the GTRI [33]. To eliminate low Reynolds number characteristics, such as laminar separations, the wind tunnel velocity was increased until a constant baseline drag was achieved.…”

“…For a rounded surface this pressure force can overcome the inertial force of the jet (i.e., the Coanda effect) inducing a curvature of the surrounding streamlines. This effect has been studied by many investigators for cylinders and modified aerofoil trailing-edge shapes [18] and particularly by Englar et al [30][31][32][33][34]. The pressure force decreases with distance from the jet nozzle exit and eventually equals the inertial force at which point the flow separates from the surface.…”

Flow Control over the Blunt Trailing Edge of Wind Turbine Airfoils Using Circulation Control

“…Figure 2 shows the sketch map of the trailing edge Coanda surface design. The procedure is given as follows: (1) Copy the upper and lower surface profile lines, and translate them inward by a distance of 0.5% chord, forming lines m and n; (2) Construct a circle with the constraint that the circle is tangent to the upper and lower translated lines m and n, as well as the trailing edge line, forming three tangency points E, F and P; (3) Connect the center point O of the circle to the two tangency points E and F, respectively, and then extend the two line segments OE and OF to intersect with the upper and lower profile lines, obtaining two intersection points C Energies 2018, 11, 619 4 of 26 and D; (4) For traditional circulation control, the whole part of the circular surface EPF is treated as the Coanda surface [21,[25][26][27], as shown in Figure 2b. This traditional CC approach is denoted as full circulation control (FCC) in the present study, in order to distinguish it from the newly proposed partial circulation control (PCC) shown in Figure 2c.…”