Dynamic Evolution of a Transient Supersonic Trailing Jet Induced by a Strong Incident Shock Wave

The dynamic evolution of a highly underexpanded transient supersonic jet at the exit of a pulse detonation engine is investigated via high-resolution time-resolved schlieren and numerical simulations. Experimental evidence is provided for the presence of a second triple shock configuration along with a shocklet between the reflected shock and the slipstream, which has no analogue in a steady-state underexpanded jet. A pseudo-steady model is developed, which allows for the determination of the post-shock flow condition for a transient propagating oblique shock. This model is applied to the numerical simulations to reveal the mechanism leading to the formation of the second triple point. Accordingly, the formation of the triple point is initiated by the transient motion of the reflected shock, which is induced by the convection of the vortex ring. While the vortex ring embedded shock move essentially as a translating strong oblique shock, the reflected shock is rotating towards its steady state position. This results in a pressure discontinuity that must be resolved by the formation of a shocklet

Numerical Simulation of Shock Wave Propagation in Ducts with Grooves

The pressure attenuation of moving shocks when they propagate in ducts, is of great importance in a wide variety of applications, such as health, safety, and transportation. The objective of this research is to simulate the propagation of shock waves in ducts with roughness. The roughness is added in the form of grooves as in an existing experiment. Different shapes are considered in order to better understand the physics behind the evolution of the complex shock patterns resulting from diffraction, reflection and refraction of the primary moving shock. The contribution of grooves and duct shape on these phenomena and pressure attenuation is investigated. The numerical method is validated through several test cases, and the results are compared against the theory and the experimental measurements. Good agreement between high resolution computations and the experiment is obtained for the shock speeds and complex wave patterns created by the grooves. Time histories of pressure at various locations are also compared. It is found that accurate pressure history agreement requires a close representation of the full experimental setup to fully capture boundary layer development, and pressure losses associated with unsteady moving shocks in long ducts. Different groove geometries have been tested in the numerical computation in order to identify the shape that will diminish shock strength, hence pressure extrema more effectively. Analysis and animations of the computed results are employed to reveal salient features of the unsteady flowfield

Mechanisms of detonation transmission in layered H 2 -O 2 mixtures

When a plane detonation propagating through an explosive comes into contact with a bounding explosive, different types of diffraction patterns, which may result in the transmission of a detonation into the bounding mixture, are observed. The nature of these diffraction patterns and the mode of detonation transmission depend on the properties of the primary and bounding explosives. An experimental and analytical study of such diffractions, which are fundamental to many explosive applications, has been conducted in a two channel shock tube, using H 2 -O 2 mixtures of different equivalence ratios as the primary and bounding or secondary explosive. The combination of mixtures was varied from rich primary / lean secondary to lean primary / rich secondary since the nature of the diffraction was found to depend on whether the Chapman-Jouguet velocity of the primary mixture, D p , was greater than or less than that of the secondary mixture, D s . Schlieren framing photographs of the different diffraction patterns were obtained and used to measure shock and oblique detonation wave angles and velocities for the different diffraction patterns, and these were compared with the results of a steady-state shock-polar solution of the diffraction problem. Two basic types of diffraction and modes of detonation reinitiation were observed. When D p > D s , an oblique shock connecting the primary detonation to an oblique detonation in the secondary mixture was observed. With D p D s . When D p > D s , the primary wave acts like a wedge moving into the secondary mixture with velocity D p after steady state has been reached, a configuration which also arises in oblique-detonation ramjets and hypervelocity drivers.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/46110/1/193_2005_Article_BF01419004.pd

Aeronautical engineering: A continuing bibliography, supplement 122

This bibliography lists 303 reports, articles, and other documents introduced into the NASA scientific and technical information system in April 1980

Advanced Turboprop Project

At the direction of Congress, a task force headed by NASA was organized in 1975 to identify potential fuel saving concepts for aviation. The result was the Aircraft Energy Efficiency (ACEE) Program implemented in 1976. An important part of the program was the development of advanced turboprop technology for Mach 0.65 to 0.85 applications having the potential fuel saving of 30 to 50 percent relative to existing turbofan engines. A historical perspective is presented of the development and the accomplishments that brought the turboprop to successful flight tests in 1986 and 1987

Aeronautical engineering: A continuing bibliography with indexes (supplement 237)

This bibliography lists 572 reports, articles, and other documents introduced into the NASA scientific and technical information system in February, 1989. Subject coverage includes: design, construction and testing of aircraft and aircraft engines; aircraft components, equipment and systems; ground support systems; and theoretical and applied aspects of aerodynamics and general fluid dynamics

Aeronautical engineering: A continuing bibliography with indexes (supplement 210)

This bibliography lists 409 reports, articles and other documents introduced into the NASA scientific and technical information system in January 1987