Sally P. Bane

Plasma Control of Combustion Instability in a Lean Direct Injection Gas Turbine Combustor

Combustion instabilitiy, despite being researched extensively for the past five decades, remains an important issue for modern propulsion and energy systems. The impact of instabilities ranges from increased loading on system components to catastrophic system failure. To date, most strategies for controlling combustion instability have involved either changing subsystem geometry or using an actuator to modify a system parameter, such as the fuel flow rate. In this paper the groundwork is laid for the use of plasmas as an active control mechanism of combustion instabilities. The discharge characteristics of two circuits are examined to determine their compatibility with the instabilities seen in an existing leandirect injection (LDI) combustion chamber. The influence of pressure on the power and energy of a circuit is also examined. Finally, future work to improve the circuits is discussed as well as plans to begin full-scale testing in the LDI combustion chamber. I. Introduction OMBUSTION dynamics and control (CDC) is a multidisciplinary field that has been studied intensely for the past 60 years 1 . The groundwork for modern CDC was laid in the 1950s and 60s when stability problems were observed in jet propulsion systems developed for rockets and aircraft. Combustion instability remains a major issue for energy and propulsion system development, from gas turbines to rocket motors to supersonic ramjet/scramjet propulsion. Combustion instability arises from the interaction of acoustic waves with the unsteady heat release by the combustion. The acoustic waves and transient heat release couple in such a way as to cause one or more of the acoustic modes of the combustion chamber to grow, resulting in high-amplitude pressure oscillations 2,3,4 . These pressure oscillations and the enhanced heat transfer can damage the structural integrity of the system and degrade performance, and may actually cause structural damage 4 . In the worst cases, combustion instability can lead to

Characterization of Flow Control Actuators Based on Spark Discharge Plasmas Using Particle Image Velocimetry

Controlling flow over an aircraft is of prime importance when attempting to improve efficiency. Delaying or inducing stall and laminar to turbulent transition are all important factors in controlling the flow. Spark plasma actuators are a promising method of manipulating both subsonic and supersonic flow. The spark plasma induces a complex local velocity field and generates vorticity in the flow. Using the particle imaging velocimetry (PIV) technique to image the flow provides a non-intrusive method of observing flow phenomenon and generating velocity fields that can quantitatively describe the induced velocity. It has been found that flow near the electrodes used to generate the spark moves toward the electrode surface initially, then moves toward the center of the gap and out toward ambient air. Induced flow velocities as high as 14 m/s in quiescent air have been observed in this experiment, with local vorticity as high as 30,000 s.

Time-resolved measurements of electron density in nanosecond pulsed plasmas using microwave scattering

In this work, Rayleigh microwave scattering was utilized to measure the electron number density produced by nanosecond high voltage breakdown in air between two electrodes in a pin-to-pin configuration (peak voltage 26 kV and pulse duration 55 ns). The peak electron density decreased from 1*10^17 cm^-3 down to 7*10^14 cm^-3 when increasing the gap distance from 2 to 8 mm (total electron number decreased from 2*10^13 down to 5*10^11 respectively). Electron number density decayed on the timescale of about several microseconds due to dissociative recombination.

Numerical Modeling of a Wave Turbine and Estimation of Shaft Work

Wave rotors are periodic-flow devices that provide dynamic pressure exchange and efficient energy transfer through internal pressure waves generated due to fast opening and closing of ports. Wave turbines are wave rotors with curved channels that can produce shaft work through change of angular momentum from inlet to exit. In the present work, conservation equations with averaging in the transverse directions are derived for wave turbines, and quasi-one-dimensional model for axial-channel non-steady flow is extended to account for blade curvature effects. The importance of inlet incidence is explained and the duct angle is optimized to minimize incidence loss for a particular boundary condition. Two different techniques are presented for estimating the work transfer between the gas and rotor due to flow turning, based on conservation of angular momentum and of energy. The use of two different methods to estimate the shaft work provides confidence in reporting of work output and confirms internal ___________________________________________________________________ This is the authors manuscript of the article published in final edited form as: Jagannath, R. R., Bane, S. P. M., & Razi Nalim, M. (2018). Numerical Modeling of a Wave Turbine and Estimation of Shaft Work. Journal of Fluids Engineering, 140(10), 101106-101106–101113. https://doi.org/10.1115/1.4040015 ASME Journal of Fluids Engineering FE-17-1279 Bane 2 consistency of the model while it awaits experimental data for validation. The extended wave turbine model is used to simulate the flow in a three-port wave rotor. The work output is calculated for blades with varying curvature, including the straight axial channel as a reference case. The dimensional shaft work is reported for the idealized situation where all loss generating mechanisms except flow incidence are absent, thus excluding leakage, heat transfer, friction, port opening time and windage losses. The model developed in the current work can be used to determine the optimal wave turbine designs for experimental investment.

Fluid Motion Induced by Spark Plasma: Development of Particle Image Velocimetry Measurements

There has been increased interest in the use of plasma actuators for flow control in aerodynamics and combustion to improve efficiency and reduce emissions. Spark plasma actuators have capabilities of inducing heat and momentum to the flow field. The flow field generated by this plasma induces complex pressure and temperature gradients that lead to the development of complex flow structures. The experiment described in this research is particularly difficult due to its small scale, and the dynamic range of velocities that are induced by the flow field. This flow field is yet to be quantified by previous research. The purpose of this experiment is to develop a method of capturing and processing the flow field generated to present accurate results of the flow induced by the spark. A 2-D PIV system is used to capture the images and the appropriate pulse separation and a 48 x 48 pixel interrogation window size are chosen to analyze the flow field induced by 3 different electrode configurations. The repeatability of the flow field is assessed and the turbulent nature of the flow field is revealed. Voltage measurements show that there is varying deviation in the voltage during the spark. Analysis of the flow field shows 70-90% deviations in magnitude of velocity. The effects of using ensemble averaging, ensemble correlation and correlation of ensemble images on maximizing signal to noise ratio (SNR) is assessed. Preliminary results show flow concentrated in the center of the electrode gap at initial times, followed by an outward flow toward the surrounding gas.