Summary of Recent Research on Detonation Wave Engines at UTA
A survey of recent research at UTA on detonation waves related to propulsion is presented in this paper. A brief historical review of the early pulse detonation engine (PDE) research at UTA is provided to lay the background for the development of a large-scale PDE Ground Demonstrator. Also current activities related to the development of rotating detonation wave engines (RDE) are reviewed. System integration studies for both PDE- and RDE-based propulsion systems are summarized, followed by a brief description of two programs focusing on application of detonation waves to hypersonic flow simulation and power generation.
OVERVIEW OF THE NASA MARIAH PROJECT AND SUMMARY OF TECHNICAL RESULTS
During the period April 1995 to October 1997, the National Aeronautics and Space Administration (NASA) sponsored the Magnetohydrodynamics Accelerator for Research Into Advanced Hypersonics (MARIAH) Project. The objective of the project was to evaluate MHD as a driver technology for hypersonic ground test facilities. Test requirements developed in consultation with NASA specified that the technology should be capable of supporting near full-scale engine testing at dynamic pressures up to 2,000 lbf/ft2 and free stream Mach numbers up to 16. Test durations of tens of seconds to minutes were also specified. The near full-scale requirement implies large test section areas, large flow rates, and extremely high electric power. A technology evaluation included a review of past United States and Russian magnetohydrodynamics (MHD) technology development, detailed analysis and computational simulation of several configurations of MHD accelerators, and two major experimental efforts directed at measurement of electrical conductivity in seeded and unseeded high pressure air. One of the significant findings of the MARIAH Project is that MHD accelerators, which rely on thermal ionization of an alkali metal to achieve the requisite conductivity, have a restricted pressure-temperature range of operation. Pressures of at least 100 atm and temperatures of 2,500 K or higher are required for this mode of MHD channel operation, irrespective of seed material. This is due in part to constraints on entropy dictated by the targeted test section conditions. The minimum temperature requirement of 2,500 K is determined by electrical conductivity considerations. This temperature-pressure range is difficult to achieve using conventional arc heaters as primary drivers. Consequently, alternative nonequilibrium schemes for creating and sustaining the electrical conductivity were investigated. Unconventional drivers in the form of ultrahigh pressure (UHP) gas piston drivers were also evaluated. This paper discusses the major activities and technical findings, concluding with specific recommendations for future research.
Shape and surface texture of molten droplets deposited on cold surfaces
When a molten droplet impacts on a cold surface, the interaction between solidification and fluid dynamics can lead to different shapes and surface textures of deposited droplets. This article presents an experimental study on deposition of small droplets (39 μm diameter) of molten wax ink on solid surfaces. Our results show that both the final shape and the surface texture of deposited droplets are extremely sensitive to deposition conditions, which include initial temperature of droplets, type of substrate surface and distance between substrate and printhead. Different surface textures are observed and shown to depend on the thermal and flow histories of ink droplets during the process of impact. A test using crystalline wax reveals crystallization as one of the major factors in determining the final texture.