Mary Ann Clarke

Design of a compact quarter wave coaxial cavity resonator for plasma ignition applications

Atmospheric and higher pressure RF and microwave plasma sources have numerous applications including material processing and spectroscopy. More recently, advantages in using such discharges for combustion ignition are being investigated. A particularly simple and compact microwave discharge generating device is the quarter wave coaxial cavity resonator (QWCCR). This paper presents a new, compacted design of such a device. A simple approximate analysis of the quality factor, Q, which is a measure of the resonant electromagnetic potential step-up capability is given, and compared to experimentally measured quality factors showing reasonable agreement. Analytic results indicate that the foreshortened folded cavity quality factors are comparable to tapered coaxial cavity designs.

Investigation Into the Feasibility of an Augmented Propeller Design With the Use of a Passive Circulation Control System

Circulation control is a high-lift methodology that can be used in a variety of fluid dynamic systems, such as, on the wing of an aircraft. Circulation control increases the near surface velocity of the airflow over a rounded surface of an object, typically a slightly modified airfoil. This is primarily achieved though the addition of a jet of air to a specially designed aircraft wing using a series of blowing slots that eject pressurized high velocity (above the free-stream velocity) jets of air over the trailing edge and/or leading edge. Studies have also been conducted into the addition of circulation control to bodies such ad propellers and rotors. In the early years of circulation control there were three main critical design issues with the addition of circulation control to a rotating body. The first being the exposure of the rotors angles of attack between 0–35° caused by the inflow of air through the propeller plane. Through the study of high angles of attack in wind tunnel testing, it is possible to predict the behavior of the rotor blade at these higher angles of attack. The second obstacle in the prior applications of circulation control to a propeller was the inability to achieve the response times necessary to effectively use circulation control during the rotation of the propeller. A further requirement of circulation control applications to propeller powered aircraft is the power required to supply the airflow. An active circulation control system uses an internal pumping system which can use power from the aircraft or from an additional power source, such as a generator, to pressurize the air plenums in order to use circulation control on the aerodynamic body. With the development of unmanned aerial vehicles (UAVs), propeller performance enhancement is desirable in order to increase the thrust, and/or the overall range of the aircraft. The application of the active circulation control to the propeller, though potentially beneficial, is currently envisioned as creating technical difficulties in the supply of air to the circulation control blowing slot. A passive system in which air can be supplied to a strategically placed circulation control blowing slot can also enhance the performance of a propeller. The proposed passive system will take advantage of the pressure differential upstream and downstream of the propeller plane, forward air velocity, stagnation pressure, and centripetal acceleration to pressurize the internal plenum of the circulation control system and thus not require an additional power source to augment the propeller of the aircraft. Also, because the system will not need to be pressurized from an outside source, no additional weight or requirements will be necessary for the aircraft other than the implementation of an updated propeller. It has been shown that through the addition of a pressure capture device on the front of a propeller, a six to fourteen percent increase in lift coefficient can be achieved simply by allowing the stagnation air ahead of the propeller to pressurize the internal plenums. Although not significant for use in larger propeller driven aircraft, for UAV applications, this can lead to a two to five percent increase in range.Copyright

Complete Command, Control, Communications, Intelligence, Surveillance, and Reconaissance System for C-130 Aircraft

Utilization of existing airframes for multi-mission capabilities has become a driving factor for defense agency sponsored research and development work. This concept stems from the obvious cost and versatility discrepancy between development of specialized aircraft for specific mission use and development of nonpermanent add-on componentry for existing aircraft. A well established and used aircraft that can benefit from nonpermanent add-on components is the C-130. With over 50 years of military theater use and well over 2000 units produced, the C-130 aircraft has both multi-agency availability and multi-mission capability to benefit from this concept. The proposed dual agency system concentrates on mission use relating to both high and low altitude surveillance and reconnaissance. The base structure of the system is a sensor deployment platform (Oculus) developed at West Virginia University and the data generation/collection/interpretation component of the system which was developed at the Air Force Research Laboratory. Each system is described individually in depth along with their role in association together. In collaboration the dual organization system provides military defense agency’s with the first nonpermanent, mobile Command, Control, Communications, Computers, Intelligence, Surveillance and Reconnaissance aircraft system.

Effect of Leading Edge Blowing Slots on Stall Angles of a 10:1 Elliptical Airfoil

Traditional uses of circulation control have been studied since the early 1960’s and have been developed primarily using trailing edge slots over a rounded trailing edge in order to take advantage of the Coanda effect. The leading edge activated slots allow jets of air to enter the freestream flowing around the airfoil thus enhancing the energy of the lift force. The main purpose of circulation control for fixed wing aircraft is to increase the lifting force when large lifting forces and/or slow speeds are required, such as at take-off and landing. While there is a significant increase in the lifting forces achievable through the use of circulation control, there is also an inherent increase in the drag force on the airfoil (Abramson, 2004, Loth, 1976, 1984). Current effects of circulation control on stall angles of airfoils are not well documented and thus needs to be studied. Stall occurs when a sudden reduction in lift occurs caused by a flow separation between the incoming air flow and the lifting surface. The angle at which this happens is commonly called the critical angle of attack, and is typically between eight and twenty degrees depending on the wing profile, aspect ratio, camber, and planform area. For this study, a 10:1 aspect ratio elliptical airfoil with a chord length of 11.8 inches and a span of 31.5 inches was inserted into the West Virginia University Closed Loop Wind Tunnel and was tested at varying wind speeds (80, 100, and 120 feet per second), angle of attack (zero to sixteen degrees), and blowing coefficients, ranging from 0.0006 to 0.0127 depending on internal plenum pressure. By comparing the non-circulation controlled wing with the active leading edge slot circulation control data, a trend was found as to the influence of the circulation control exit jet on the stall characteristics of the wing. For this specific case, when the circulation control is in use on the 10:1 elliptical airfoil, the stall angle decreases, from eight degrees to six degrees, while providing up to a 46% increase in lift coefficient.Copyright

Pitch Stability of an Unpowered Ground Effect Vehicle

The ground effect regime was first utilized in the early 1900’s with the advent of transatlantic flight. Aircraft such as the Dornier DO-X would fly close to the surface of the water in order to increase its payload and range. Since that time, research has been periodic with the largest resurgence of ground effect interest in the 1960’s. The Russian government became involved in developing aircraft designed solely for ground effect flight. The design of these aircraft was difficult due to the inherent problems that exist within ground effect. There are natural instabilities that occur, especially in the longitudinal direction that are antagonized by shifting payload weights. Past researchers have handled the unique design requirements of ground effect through the usage of high-tail devices which operate outside of ground effect and power augmented ground effect which artificially generates the lift force through the use of thrust vectoring. The Center for Industrial Research Applications (CIRA) has developed a single passenger, unpowered, subsonic aircraft that relies on gravitational forces for momentum. AirRay combines the benefits of ground effect i.e. the increased lift and decreased induced drag, with a unique approach to maintaining stability. The design of AirRay faced many challenges as a result of flying in the ground effect regime, similar to those found in the prior efforts. These include natural instabilities, primarily in the longitudinal direction, that cause the glider to want to pitch up. In addition the size requirements for a single rider to maximize maneuverability, as well as the potential for updrafts on a downhill slope are added constraints to the design of the ground effect vehicle. These issues, and others, are the subject of current study. This paper has focused on the most important aspect of the design, longitudinal stability. This research has shown positive results with respect to the effectiveness of slots, on passively controlling the movement of the center-of-pressure at varying angles of attack. The 40 degree slot located at 20% of the chord line was most advantageous in stabilizing movement. These results indicate a craft can be designed that can be stable and function in the majority of the flight conditions that have been specified.Copyright

Elliptic Airfoil Stall Analysis With Trailing Edge Slots

Circulation control (CC) is a high-lift methodology that can be used on a variety of aerodynamic applications. This technology has been in the research and development phase for over sixty years primarily for fixed wing aircraft where the early models were referred to as “blown flaps”. Circulation control works by increasing the near surface velocity of the airflow over the leading edge and/or trailing edge of a lifting surface This phenomenon keeps the boundary layer jet attached to the wing surface thus increasing the lift generated on the surface. The circulation control airflow adds energy to the lift force through conventional airfoil lift production and by altering the circulation of stream lines around the airfoil. For this study, a 10:1 aspect ratio elliptical airfoil with a chord length of 11.8 inches and a span of 31.5 inches was inserted into the West Virginia University Closed Loop Wind Tunnel and was tested at varying wind speeds (80, 100, and 120 feet per second), angle of attack (zero to sixteen degrees), and blowing coefficients, ranging from 0.0006 to 0.0127 depending on plenum pressure. By comparing the non-circulation controlled wing with the active circulation control data, a trend was found as to the influence of circulation control on the stall characteristics of the wing for trailing edge active control. For this specific case, when the circulation control is in use on the 10:1 elliptical airfoil, the stall angle decreased, from eight degrees to six degrees, while providing a 70% increase in lift coefficient. It should be noted that due to the trailing edge location of the circulation control exit jet, a “virtual” camber is created with the free stream air adding length to the overall airfoil. Due to this phenomena, the actual stall angle measured increased from eight degrees on the un-augmented airfoil, to a maximum of twelve degrees.Copyright

Testing of a Sliding Gate Valve for Circulation Control Wind Turbines

The application of circulation control to vertical axis wind turbines is currently being investigated as a means to increase efficiency across a broad range of wind speeds. One of the key technical hurdles of this application is the valve mechanism for controlling the airflow out of the blowing slots on each of the blades. Due to the inherent nature of such a system, many conventional valves are ill fitted for this application, as an emphasis is placed on size, weight, response time and overall power requirements. A valve design consisting of a slotted, sliding gate mated to a slotted, fixed surface within the wind turbine blade is presented. The sliding gate is actuated via a solenoid, forcing the slots into alignment and allowing air to flow freely. The gate is returned via a spring, forcing the slots out of alignment and restricting the flow of air. A testing apparatus was fabricated so that the response time, power requirements and leakage rates could be measured. Response times of less than 20 ms to open the valve are achievable with 100 W of power at the solenoid, with a closing time of less than 14 ms. The leakage through this closed valve design was measured at up to 11% of the open condition, which will require a redesign of the seating arrangement.