No abstract

Owing to its ability to alleviate the compressibility effect on the advancing side, the slowed rotor operating at high advance ratios is a key feature in high-speed compound rotorcraft. A series of wind tunnel tests were conducted in the Glenn L. Martin Wind Tunnel with a four-bladed Mach-scaled articulated rotor. The objective of the tests was to gain a basic understanding of unique features of high-advance-ratio aerodynamic phenomena, such as thrust reversal and dynamic stall in the reverse flow region. In this study, high-advance-ratio tests were carried out with highly similar, noninstrumented blades and on-hub control angle measurements, to minimize possible error due to blade structural dissimilarity and pitch angle discrepancy. The tests were conducted at 900 and 1200 RPM, advance ratios of 0.3–0.9, and a shaft tilt study was conducted at±4°. Pitch and flap motion at the blade roots, rotor performance, and vibratory hub loads were investigated during the test. The test data were then compared with those of previous tests and with predictions from comprehensive analysis. The airload results were investigated using comprehensive analysis to gain insights into the influences of advance ratio and shaft tilt angle on rotor performance and hub vibratory loads. Results indicate that the thrust benefit from backward shaft tilt is dependent on the change in the inflow condition and the induced angle of attack increment, and the reverse flow region at high advance ratios is the major contributor to changes in shaft torque and horizontal force.

No abstract

An experimental investigation into the flow control capabilities of synthetic jet actuators (SJAs) was performed. An array consisting of two synthetic jet actuators was designed and fabricated. The effects of vectoring an array on streamline location and pressure distribution were studied using Particle Image Velocimetry (PIV) and static pressure measurements. Three different bodies were tested: a flat plate, a two-dimensional cylinder representative of a bluff body, and a modified two-dimensional NACA 0018 airfoil representative of a streamlined body. Actuation was performed at Array Momentum Coefficient (Cµ) values ranging from 0.8% to 8%. The relative phase of operation, ϕ, of the individual actuators in the array was varied to control the direction of the jet trajectory. PIV was used to study the streamline deflection pattern over a flat plate. A significant change in streamline deflection pattern was observed in response to changing the phase. For the case of the cylinder, actuator arrays were placed at +/-70° locations with respect to the free stream direction. Actuation was performed at a momentum coefficient value of approximately 0.8% and the phase was varied. Pressure measurements were made over the surface of the cylinder. A 10% decrease in pressure drag was observed for specific cases of phasing. Pressure measurements indicated that the point of separation, in response to actuation at this specific phase angle, was delayed by approximately 20°. An array of actuators was also embedded in a modified NACA 0018 airfoil subjected to a low speed cross-flow. The pressure coefficient (CP) was calculated over the surface. For this case, vectored actuation resulted in a reduction in pressure drag and a simultaneous increase in lift. The benefits of phased actuation over different types of aerodynamic bodies are demonstrated and analyzed using different experimental methods. Nomenclature φ = Operating phase difference between array actuators 1 and 2 b = Streamwise dimension of orifice (width) c = Characteristic Length Scale (used for calculating Cμ and F*) Cμ = Actuator/Array Momentum Coefficient (2bUJ 2 / cU 2 ) CD = Drag coefficient CL = Section Lift coefficient

No abstract