Kenneth Granlund

The management of flow around supersonic aircraft, and also internal flows in engine inlets and weapons bays has been a constant topic mainly to the defense community of research since for the last half-century. Observations of fluctuating aerodynamic flow phenomena is done through shadowgraph flow visualizations are imaged by digital cameras. What is more difficult is true unsteady flows when the actual geometry itself is deforming. For many relevant problems, this rate-of-change becomes impossibly fast to duplicate in available supersonic wind tunnels. By means of a mathematical analogy, two-dimensional supersonic flows with associated internal and external shock structures can be visualized as hydraulic jumps (waves) on a thin sheet of water flowing at low speed <1 m⁄s over a glass table.

Wall-cavities exposed to high-subsonic or supersonic free streams have been studied for several decades in order to understand and model the aeroacoustic resonance effect from the unstable shear layer over the cavity impinging on the aft wall, causing recirculation and acoustic resonance. Low-order models have been developed, and suppression mechanisms have been conceived from a frequency-domain analysis of experiments. Here, we study the transient operation of the startup-shutdown of the cavity resonance by implementing sliding doors that cover the cavity with the aim to extend the aerodynamic models of cavity resonance to incorporate initial conditions in the time domain.

This project will focus on the model-based design, flight characterization, robust periodic control, 1/10-scale prototyping, and testing of a rigid kite-based ocean current and tidal energy harvesting system. The system is intended for areas of moderate flow in relatively shallow waters, one example being the shallow waters adjacent to the Gulf Stream. The proposed system will consist of a high lift/drag rigid wing that executes periodic cycles. Each cycle will consist of a high-tension cross-current spool-out phase, followed by a low-tension spool-in phase. The use of multiple control tethers and/or on-board control surfaces will make it possible to achieve and control this desired periodic motion in a manner that is robust to fluctuations and uncertainties (e.g., ocean current speed/direction, etc.). It has been demonstrated that properly controlled periodic motions can lead more than an order of magnitude increase in net energy production over equivalently-sized stationary devices, or equivalently, the same amount of power as a stationary system using an order of magnitude less material. The proposed research will focus on two candidate kite-based system configurations: (i) A system where the electric motors/generators and power electronics are housed on a floating platform out of the water and (ii) a system where they are housed at the seabed, in shallower waters.

The purpose of this project is to investigate the magnitude of lift and pitching moment variation during an unsteady vs. the quasi-steady translation of a slender body from a cavity through a vortex-shear layer into supersonic flow. Mean- and time-varying, as well as frequency content of the normal force and pitching moment will be recorded. To correlate the forces on the store, simultaneous flowfield information, as well as surface pressure data will be obtained. The future application is to investigate whether timed-release of stores from cavities offer a benefit in a more accurate prediction of safe trajectory from the air vehicle.