Frank K. Lu

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.

Advanced hypersonic test facilities

Hypersonic Ground Test Requirements Principles of Hypersonic Test Facility Development NASAs HYPULSE Facility at GASL The LENS I and II Hypervelocity Tunnels and Application to Hypersonic Vehicle Testing Under Fully Duplicated Flight Conditions The U-12 Large Shock Tube Detonation-Driven Shock Tubes and Tunnels Aerothermodynamics Research in the DLR High Enthalpy Shock Tunnel HEG Characteristics of the HIEST and its Applicability for Hypersonic Aerothermodynamic and Scramjet Research Piston Gasdynamic Units with Multicascade Compression Arc-Heated Facilities The SCIROCCO 70-MW Plasma Wind Tunnel Aerodynamic and Propulsion Test Unit Arc-Heated Facilities (LBK) as a Tool to Study Aerothermodynamic Problems of Reentry Vehicles The NASA Langley Research Center 8-ft High Temperature Tunnel NASA Glenn Research Centers Hypersonic Tunnel Facility The ONERA F4 High-Enthalpy Wind Tunnel The AEDC Hypervelocity Wind Tunnel 9 A Hypersonic Ground-Test Facility Using Magnetic Levitation and Electromagnetic Propulsion Recent Increases in Hypersonic Test Capabilities at the Holloman High Speed Test Track and Design of a Magnetically Levitated Test Track Capability Increased Launching Capabilities at AEDCs Range/Track G A New Mach 8-15 True Temperature Test Facility Concept to Meet the U.S. Shortfall in Hypersonic Test Capability New-Generation Hypersonic Adiabatic Compression Facilities with Pressure Multipliers

Experimental Study of Near Wake of Micro Vortex Generators in Supersonic Flow

Detailed schlieren and laser lightsheet visualizations of the near wake of micro vortex generator (MVG) revealed large structures that were different from those of the undisturbed turbulent boundary layer. These structures were attributed to the rapid breakdown of the primary trailing vortex pair. The breakdown was thought to arise from a cylindrical Kelvin–Helmholtz-like instability surface. The structures appear to be hairpin or ring-like in nature that showed eruptions into the freestream flow, entraining it.

Numerical and Experimental Studies on the Separation Topology of the MVG Controlled Flow at M=2.5

In this paper, the implicitly implemented LES method and fifth order bandwidth optimized WENO scheme are used to make comprehensive studies on the separation topology of the MVG controlled flow at M=2.5 and Re{\theta}=5760. Experiments are also made to verify the prediction of the computation. Analyses are conducted on three categories of the topology: the surface separation, cross-section separation and the three dimensional structure of the vortices. A complete description about the separation topology and a series of new findings are obtained. Among them, a pair of spiral point is first predicted by the computation and verified by the experiment. A corresponding new vortex model with 7 vortex tubes is presented also.

Shock/boundary-layer interaction effects on transverse jets in crossflow over a flat plate

Shock/boundary layer interaction alters the near field mean flow of a transverse jet in supersonic crossflow by bifurcating the phase portrait of the separation topology through the addition of saddle points, nodes and separation lines. Moreover, the interaction generates additional flow structure in the near field that affects the surface pressures and ultimately the jet interaction performance coefficients. This study examines the flow structure, separation topology and performance characteristics of an underexpanded transverse jet issuing normally into subsonic and supersonic freestreams. New flow structure in the near field of the jet has been identified adding to the basic understanding of jet interaction.

Downstream influence scaling of turbulent flow past expansion corners

Previous studies of the high-speed viscous inviscid interaction between a turbulent boundary layer and an expansion at a convex corner have noted that surface pressure decreases toward the downstream inviscid value yielded by a Prandtl-Meyer expansion. A downstream influence on the corner is presently identified which is based on the mean surface pressure distribution; a scaling law is proposed for this distance.

Review of Micro Vortex Generators in High-Speed Flow

A review of the state-of-the-knowledge of micro vortex generators (MVGs) and their effect on separated shock/boundary-layer interactions is provided. MVGs are thought to be effective for reducing the separation zone. However, details of how they affect the separation zone remain to be understood properly. In addition, metrics on how the MVGs affect the separation have not been well developed. Suggestions for further study are provided.

Exergy analysis of a pulse detonation power device

Recent research has been developed in thermodynamic analysis of pulse detonation engines. However, the focus of contemporary work is on thrust production for propulsion systems. The present work develops an exergy analysis of a pulse detonation power device. The objective of this analysis is to quantify the efficiency, in terms of availability, of a power device operated by detonation. This study considered the fuel availability and the losses in the system. Losses are due to irreversibilities during processes and due to availability transfer. The Second Law or exergetic efficiency was computed based on the fuel availability. The device modeled here embraces a low pressure compressor, a check valve, a detonation chamber, a two stage turbine and a generator. The results are then compared with the exergetic efficiency applied to deflagration systems. Data for detonation and deflagration were obtained from C.E.A. code (McBride and Gordon, 1994), using two different hydrocarbon fuels: methane (CH4) and propane (C3H8). The results of this study show that detonation is a much more energetic process than deflagration, and the exergy analysis makes clear that this device is efficient for power generation.

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.

Experimental and Numerical Study of Flow Topology Past Micro Vortex Generators

Detailed experimental and numerical visualizations of the flow past a micro vortex generator (MVG) in the form of a ramp with swept sides in a Mach 2.5 flow revealed a complex near-field topology. The incoming flow separated over the leading edge of the MVG despite the ramp angle being below the threshold for incipient separation. The separation over the MVG protuberance produced a weak trailing horseshoe vortex system. The attachment line shows a saddle/foci combination on each side of a nodal point of attachment. The flow over the top of the MVG separated off the slant edges to produce a large primary vortex pair. This large primary vortex pair induced two secondary vortex filament pairs, one off the top of the MVG and another at the corner of the MVG with the flat plate. Extra complexities were revealed at the trailing edge with at least two pairs of saddle/foci combinations observed. It is postulated that vortex filaments spring from the various saddle/foci combinations as these were not observed experimentally or computationally. Symmetry breaking due to flow unsteadiness was also observed in the MVG wake.