Eric M. Braun

Rotating Detonation Wave Propulsion: Experimental Challenges, Modeling, and Engine Concepts

Rotating detonation engines (RDEs), also known as continuous detonation engines, have gained much worldwide interest lately. Such engines have huge potential benefits arising from their simplicity of design and manufacture, lack of moving parts, high thermodynamic efficiency and high rate of energy conversion that may be even more superior than pulse detonation engines, themselves the subject of great interest. However, due to the novelty of the concept, substantial work remains to demonstrate feasibility and bring the RDE to reality. An assessment of the challenges, ranging from understanding basic physics through utilizing rotating detonations in aerospace platforms, is provided.

Testing of a Continuous Detonation Wave Engine with Swirled Injection

Two different continuous detonation wave engines with swirl to improve mixing were developed. The reactants were ignited with an ordinary automotive spark plug. Mixing and detonation occurred in a common annular chamber in the first engine but occurred separately in the second. Deflagration-to-detonation transition could be observed in the first engine. The number of revolutions of the detonation wave was limited due to the inability of the supply to deliver sufficient flow. For the second engine, detonations were sustained for a longer duration. The data indicate that detonation was achieved with multiple detonation waves traveling in one direction. Adding an endcap raised the pressure in the detonation chamber.

Supersonic blowdown wind tunnel control using LabVIEWTM

A computer-based, proportional-integral control system for supersonic blowdown wind tunnels was developed in a LabVIEW environment. The control algorithm is based on numerically integrating the differential equations used to model a supersonic blowdown wind tunnel in which the proportional and integral control terms were added and tuned in a simulation to determine their appropriate values. Values for these control terms can be obtained using a spreadsheet allowing for variation of the test section Mach number, test section area, stagnation pressure and plenum chamber volume as well as the pressure, temperature and volume of the storage tank. Accounting for the variation of many terms allows the control terms and resulting LabVIEW program to be easily integrated across different facilities. Experimental verification is provided along with a discussion of control valve calibration, optimization of control constants and additional capabilities of LabVIEW.

Detonation Engine Performance Comparison Using First and Second Law Analyses

A performance comparison between airbreathing pulsed detonation engine (PDE) and rotating detonation wave engine (RDWE) concepts is made. The ight speed range used for the analysis is approximately Mach 1{5, which is typically thought to be where these concepts are viable and perhaps competitive with each other and Brayton cycle engines. Since the RDWE is ideally capable of operation with a steady state inlet and nozzle, a PDE model with similar steady state systems was developed. The comparison shows a PDE is more e cient at low supersonic speeds, but the relative RDWE performance gradually increases until it becomes comparable. The thermodynamic cycles of these detonationbased engines have been examined in detail using the Second Law to show the losses associated with mixing and purging. Additionally, the combination of an exergy analysis with First Law performance benchmarks proves to be a useful approach for optimization since sources of losses and component interrelationships are easier to identify.

A Critical Review of Electric and Electromagnetic Flow Control Research Applied to Aerodynamics

*† ‡ Fifty years ago, publications began to discuss the possibilities of electromagnetic flow control (EMFC) to improve aerodynamic performance. This led to an era of research that focused on coupling the fundamentals of magnetohydrodynamics (MHD) with propulsion, control, and power generation systems. Unfortunately, very few designs made it past an experimental phase as, among other issues, power consumption was unreasonably high. Recent proposed advancements in technology like the MARIAH hypersonic wind tunnel and the AJAX scramjet engine have led to a new phase of MHD research in the aerospace industry, with many interdisciplinary applications. Aside from propulsion systems and channel flow accelerators, electromagnetic flow control concepts applied to control surface aerodynamics have not seen the same level of advancement that may eventually produce a device that can be integrated with an aircraft or missile. Therefore, the purpose of this paper is to review the overall feasibility of the different electric and electromagnetic flow control concepts. Emphasis is placed on EMFC and experimental work.

Experimental study of a high-frequency fluidic valve fuel injector

Fuel injectors composed of an ori ce connected to a small plenum cavity were mounted on a detonation tube. These fuel injectors, termed uidic valves, utilize their geometry and a supply pressure to deliver fuel and contain no moving parts. Behavior of these uidic valves is characterized in order to determine their feasibility for integration with high-frequency pulsed or rotating detonation wave engines. Fuel ow is initiated just prior to ignition of the detonation tube to understand the interaction between the uidic valves and the wave. Parametric studies have been conducted with the type of fuel injected, the ori ce diameter, and the plenum cavity pressure. Results indicate that the detonation wave pressure temporarily shuts o the uidic valve supply, but the wave products can be quickly expelled by the fresh fuel supply to allow for refueling. The interruption time of the valve scales with the injection and detonation wave pressure ratios as well as a characteristic time.

Experimental Study of a High-Frequency Fluidic Valve Fuel Injector

Fuel injectors composed of an ori ce connected to a small plenum cavity were mounted on a detonation tube. These fuel injectors, termed uidic valves, utilize their geometry and a supply pressure to deliver fuel and contain no moving parts. Behavior of these uidic valves is characterized in order to determine their feasibility for integration with high-frequency pulsed or rotating detonation wave engines. Fuel ow is initiated just prior to ignition of the detonation tube to understand the interaction between the uidic valves and the wave. Parametric studies have been conducted with the type of fuel injected, the ori ce diameter, and the plenum cavity pressure. Results indicate that the detonation wave pressure temporarily shuts o the uidic valve supply, but the wave products can be quickly expelled by the fresh fuel supply to allow for refueling. The interruption time of the valve scales with the injection and detonation wave pressure ratios as well as a characteristic time.

Interference Drag Modeling and Experiments for a High-Reynolds-Number Transonic Wing

Multidisciplinary Design Optimization (MDO) studies show the Strut/Truss Braced Wing (SBW/TBW) concept has the potential to save a significant amount of fuel over conventional designs. For the SBW/TBW concept to achieve these reductions, the interference drag at the wing strut juncture must be small compared to other drag sources. Computational Fluid Dynamics (CFD) studies have indicated that the interference drag is small enough to be manageable. However, the RANS formulation and turbulence models used in these studies have not been validated for high Reynolds number transonic junction flows. This study assesses turbulence models by comparing flow separation characteristics obtained from experiment and CFD. The test model used is a NACA 0012 wing of aspect ratio 2 at Mach number of 0.76 and a Reynolds number of 6 million with varying angle of attack. The CFD study involved an 18.8 million cell structured grid of the wind tunnel test section using the ANSYS Fluent 12.0 solver. The k-ω SST turbulence model was the main turbulence model employed. Experiments were conducted in a high Reynolds number transonic Ludwieg tunnel. The wing was tested at different Mach numbers and inlet conditions to account for some of the experimental variations. Porous walls eliminate shock reflection across the tunnel. Surface oil flow visualization is used to indicate the interference flow patterns. The assessment shows CFD overpredicts separation and therefore interference drag, likely due to deficiencies in the turbulence model. Nomenclature

Proof-of-Principle Detonation Driven, Linear Electric Generator Facility

A facility has been constructed in which a detonation-driven piston system has been integrated with a linear generator to produce electricity. Their integration is made possible with a mass-spring system that causes the piston to freely oscillate. The piston may then drive a slider containing neodymium magnets through a generator coil. Two facility setups are described. In the rst setup, the piston is contained in a single mass, twospring system where the detonation wave pressure may be modeled as a variable force. Pressure, load, and linear translation data are collected to characterize the performance of the system. Atmospheric initial mixtures of oxygen with hydrogen, propane, and methane were detonated. A load wall is removed for the second setup where a linear motor was rewired as a passive generator for a two-mass, four-spring system proof-of-concept test. Future work and overall potential of the facility is discussed.

Refurbishment and Testing Techniques in a Transonic Ludwieg Tunnel

Although cryogenic wind tunnels are typically used in industry for transonic testing, Ludwieg tunnels with high charge tube pressures can also produce unit Reynolds numbers high enough to match inight conditions. A brief timeline of transonic Ludwieg tunnel development is presented that shows how it was nearly selected for full-scale construction to compliment the National Transonic Facility. Having recently been refurbished, an overview of the unique high Reynolds number facility at UT Arlington is presented. Currently, experiments with the facility have been conducted using a combination of porous and solid walls with a half-span NACA 0012 model. Surface ow visualization techniques are discussed for this high Reynolds number, short duration facility. Future development e orts are presented to keep the facility suitable for current transonic testing topics.