David Keisar

Massachusetts Institute of Technology | MIT · Department of Mechanical Engineering

Pulsed dielectric barrier discharge (DBD) plasma actuators were evaluated for the control of flow separation from the V-tail panels of a well-known unmanned air vehicle, using lightweight high-voltage generators. Following risk-reduction airfoil experiments, full-scale experiments were performed on an unswept tapered V-tail panel at typical takeoff...

Dynamic stall is exploited to produce positive torque on a large-chord/radius-ratio (c∕R) vertical-axis wind turbine. An elementary kinematic analysis shows that the blades experience large variations in angle of attack that produce deep dynamic stall, combined with large relative dynamic pressure variations, that are phase shifted by approximately...

A novel positive displacement, high pressure, vertical axis wind pump (HP-VAWP) was evaluated for the application of stand-alone high-pressure reverse-osmosis desalination and drip irrigation systems. The direct interface between a vertical axis wind turbine (VAWT) and a positive displacement pump, that delivers a constant volume of liquid per revo...

DBD plasma actuators were implemented on a two-bladed rotor model, and the effect of pulse-modulated actuation was evaluated at tip Reynolds numbers of 100,000 and 150,000. A parametric study showed significant blade drag reduction at pulsation frequencies around unity, a mild sensitivity to reduced frequency, and a small effect of duty cycle. In g...

Recently, a fluidic facemask concept was proposed to mitigate the transmission of virus-laden aerosol and droplet infections, such as SARS-CoV-2 (COVID-19). This paper describes an experimental investigation of the first practical fluidic facemask prototype, or “Air-Screen”. It employs a small, high-aspect-ratio, crossflow fan mounted on the visor...

A two-element natural laminar flow airfoil-commonly used on medium-altitude, long-endurance, unmanned air vehicles-was conformally decambered for application on a two-bladed, H-rotor, vertical-axis wind turbine. Blade kinematics were used to determine the virtual camber line, which was then used to conformally map the original profile onto the chor...

Dynamic stall on the blades of low-solidity vertical axis wind turbines (VAWTs) is a major problem due to its adverse effects on performance, drive-train components, and generator sizing. However, when the turbine chord-to-radius ratios are relatively large, greater than approximately 0.5, counterintuitively, dynamic stall can be harnessed to produ...

We achieved the first experimental validation of conformally decambered blades for VAWT applications and the first adaptation of slotted natural laminar (NLF) airfoils as VAWT blades. Torque was produced by the dynamic stall phenomenon due to large chord-radius ratios. Decambered blades produced 60% and 27% greater power and torque respectively, th...

The driving torque on vertical axis wind turbines with large chord-to-radius ratio blades, typically greater than 0.5, is generated mainly by the phenomenon of dynamic stall. In order to determine the optimum configuration, an extensive experimental study was conducted on two-bladed, H-rotor test turbine, by systematically varying the blade chord-t...

The supply of freshwater based on wind-powered desalination is technically feasible, but energetic losses associated with conventional systems necessitate new approaches. This study explores a direct wind-powered desalination (D-WPD) system using a small-scale vertical axis wind turbine (VAWT) for reverse osmosis via a high-pressure pump without el...

A novel direct wind-powered desalination (D-WPD) system for brackish water utilizes a small-scale vertical axis wind turbine to directly power a reverse-osmosis-based desalination system via a high-pressure pump without electricity generation or a system controller. A comprehensive parametric study examined the effects of feed water salinity, modul...

A novel fluidic facemask, or Air-Screen, is described and demonstrated experimentally for protection against virus-laden aerosol and droplet infections, such as COVID-19. The Air-Screen employs a small, high-aspect-ratio, crossflow fan mounted on the visor of a filter-covered cap to produce a rectangular air jet, or screen, in front of the wearer’s...

Flow separation, or stall, in axial flow turbomachinery results in a loss of pressure or compression in the case of fans and compressors, or the loss of power or thrust generation in the case of turbines. Wave-power-based Wells turbines, in particular, suffer so acutely from blade stall during normal operation, that it compromises their viability a...

Quasi-static and dynamic stall control experiments, using dielectric barrier discharge plasma actuators, were performed on a square-tipped aspect-ratio-one wing, with a NACA 0015 profile, under harmonic pitching, at a Reynolds number of 0.3M. Relatively low O(1) and relatively high O(10) pulse-modulated reduced excitation frequencies were introduce...

Dielectric barrier discharge (DBD) plasma actuators were implemented on the leading edges of Wells turbine impeller blades for the purpose of controlling leading-edge separation, and the turbine performance was recorded. Pulse-modulated perturbations at dimensionless frequencies near unity produced remarkable increases in performance. Under massive...

An elementary kinematic analysis of large chord-radius ratio (c/R) vertical axis wind turbines was performed and a small two-bladed model turbine (0.4c/R0.6) was built and tested. The analysis shows that these machines operate at low blade-speed/wind-speed ratios and hence the blades experience large changes in angle of attack, that produce dynam...

Pulse-modulated dielectric barrier discharge plasma actuators are applied to the problem of flow separation on a Hermes 450 unmanned air vehicle V-tail panel. Risk-reduction airfoil experiments were conducted followed by full-scale wind tunnel tests. Silicone-rubber based actuators were calibrated and subsequently retrofitted to both the airfoil an...

V-tail configurations are common on unmanned aerial systems (UAS), but the tail panels suffer from flow separation, resulting in loss of control during crosswind takeoff and landing. Implementing spanwise dielectric barrier discharge (DBD) plasma actuators with silicone rubber as a dielectric material both on an airfoil and on a full-scale Hermes 4...