John Vaccaro

Active Flow Control at Low Angles of Attack: Stingray Unmanned Aerial Vehicle

Active flow control using fluidic actuators, via arrays of synthetic jet actuators, was used to provide control power for the Stingray unmanned aerial vehicle in the longitudinal (pitch) and lateral (roll) directions at low angles of attack. Using this technique, the pitch and roll moments were altered such that the effect is similar to that of a deflection of conventional control effectors. The control effectiveness of the synthetic jets on the aerodynamic performance of the Stingray unmanned aerial vehicle was investigated experimentally in a wind tunnel. Global flow measurements were conducted, where the moments and forces on the vehicle were measured using a six-component sting balance. The effect of the actuation was also examined on the surface static pressure at two spanwise locations. In addition, a particle image velocimetry technique was used to quantify the flowfield over the model, both the global flowfield as well as the localized interaction domain near the synthetic jet orifice. The synthetic jets were able to alter the local streamlines and displace the boundary layer through the formation of a small quasi-steady interaction region on the suction surface of the Stingray unmanned aerial vehicles wing. Phase-locked particle image velocimetry data were acquired to provide insight into the growth, propagation, and decay of the synthetic jets impulse and their interaction with the crossflow. Furthermore, the changes induced on the moments and forces can be proportionally controlled by either changing the momentum coefficient or by driving the synthetic jets with a pulse modulation waveform. This can lead the way for future development of closed-loop control models.

Experimental and Numerical Investigation of Active Control of Inlet Ducts

The effect of steady and unsteady control jets on the performance of a very aggressive (length to exit diameter ratio, L/D, of 1.5) inlet duct was investigated. Experiments were performed for a range of inlet Mach numbers from 0.2 to 0.45 and compared with numerical simulations for the baseline flow case at an inlet Mach number of 0.45. A brand new facility was designed and built to enable various actuation methodologies as well as multiple measurement techniques. In the present work, a pair of control jets was placed in streamwise locations where flow was expected to separate. Steady and unsteady static pressure measurements, along the upper and lower walls of the duct, were performed for various combinations of actuation. The parameters that were tested include the control jets momentum coefficient, the blowing ratio, the actuation frequency, as well as different combinations of jets. It was shown that using mass flux ratio as a criterion to define flow control is inappropriate, and one needs to provide...

ACTIVE CONTROL OF INLET DUCTS

Active flow control, via steady control jets, was implemented to improve the performance of a very aggressive (length to exit diameter ratio, L/D, of 1.5) inlet duct. The experiments were performed for a range of inlet Mach number from 0.2 to 0.45. A brand new facility was designed and built to enable various actuation methodologies as well as multiple measurement techniques. In the present work, a pair of steady control jets was placed in streamwise locations where flow was expected to separate. Static pressure measurements, along the upper and lower walls of the duct, were performed for various combinations of actuation. The forcing level of the control jets as well as combinations of jets, were tested. In addition, total pressure measurements were conducted at the Aerodynamic Interface Plane (AIP) to obtain the distribution of the pressure recovery. Flow control was shown to have a substantial effect, mainly on the lower wall. It was found to be more effective at the lower Mach number where the blowing ratio was higher (for the same mass flux ratio). The data suggest that using 2-D flow control to affect a flow field that is highly three-dimensional is not optimal, and as such a spanwise varying actuation should be implemented.

Aerodynamic Performance Modification of the Stingray UAV at Low Angles of Attack

Active flow control using fluidic actuators, via synthetic jets and steady blowing jets, was used to provide control power for trimming the Stingray UAV in the longitudinal (pitch) and lateral (roll) directions at low angles of attack. Using this technique, the pitching and roll moments were altered such that the effect is similar to that of a deflection of conventional control effectors in trim. The control effectiveness of the flow control on the aerodynamic performance of the Stingray UAV was investigated experimentally in a wind tunnel. Global flow measurements were conducted, where the moments and forces on the vehicle were measured using a six component sting balance. The effect of the actuation was also examined on the surface static pressure at two spanwise locations. In addition, Particle Image Velocimetry (PIV) technique was used to quantify the velocity vector field over the model, both the global flow field as well as the localized interaction domain near the synthetic jet orifice. The synthetic jets were able to alter the local streamlines through the formation of a quasi-steady interaction region on the suction surface of the Stingray UAV’s wing. Phase locked PIV data was acquired to provide insight into the growth, propagation, and decay of the synthetic jet impulse and its interaction with the cross-flow. The changes induced on the moments and forces can be proportionally controlled by either changing the momentum coefficient or by driving the synthetic jets with a pulse modulation waveform. This can lead the way for future development of closed-loop control models.

Experimental and Numerical Investigation on the Interaction of Control Jets Inside a Low Aspect Ratio Short Duct

A combined experimental and numerical investigation of flow control actuation via a steady two-dimensional tangential control jet in a short inlet duct was conducted. Experiments were run on an inlet with a length to diameter ratio of 1.5 at a Mach number of 0.43 at both baseline and forced conditions. The setup in the numerical simulations matched the experimental tests in terms of both the physical parameters (e.g., Mach number, pressure level, etc.) and dimensions (e.g., contraction, inlet duct, control jet, etc.). Both experimental and numerical results for the base flow showed a quasi two-dimensional flow separation immediately downstream of the first (or upstream) turn on the lower surface. For the forced case it was found that actuation via a steady two-dimensional jet was able to control flow separation in the mid-span portion of the duct but was not effective towards the outer span and the side walls. The control jet increased the three-dimensionality of the flow field inside the inlet. In both cases, simulations were found to over predict separations found within the duct. This over prediction led to quantitative disagreement, nevertheless prominent flow structures were found to be qualitatively similar, and therefore, details of the three-dimensional flow field were explored based on numerical data. These structures were measured experimentally by means of pressure recovery, surface pressure distribution on the duct’s lower wall and by the volumetric flow field, which was acquired using stereoscopic PIV (SPIV). Both experimental and numerical results infer that a twodimensional control jet induces three-dimensional structures that are considerably larger than the ones found in the baseline flow field.

Experimental Investigation of Actuators for Flow Control in S-Duct Inlets

An experimental investigation of flow control actuation concepts on a short inlet duct was conducted. Concepts tested were steady blowing from both a two-dimensional jet and a spanwise varying jet. Experiments were run at an inlet Mach number of 0.43 on a very short inlet with a length to diameter ratio of 1.5. Spanwise varying jet actuation was found to be more beneficial compared to two-dimensional blowing in that the secondary flow structures could be manipulated. An optimal jet location was determined to be at the position of maximum spanwise velocity. However, the spanwise varying actuator could only manipulate the location of the secondary flow structures, not mitigate them. Both actuators resulted in a significant decrease in the spectral content of the total pressure at the AIP, especially around the centerline.