Nonequilibrium Hypersonic Stagnation Flow at Low Reynolds Numbers


Book Description

An analysis of nonequilibrium-dissociated stagnation point flow on highly cooled blunt bodies in a hypersonic stream of air or diatomic gas at low Reynolds numbers is presented. An arbitrary atom recombination rate on the surface is allowed. With the use of a continuum, thin shock layer model, it is shown that for flight speeds on the order of 25,000 ft/sec or less, the problem can be broken down into two regimes, both of which can be treated analytically with good approximation. The first is a generalized nonequilibrium vorticity-interaction flow regime where most of the significant gas phase reaction effects occur, including the transition from recombination rate to dissociation rate-controlled behavior. The closed form solutions given for this regime predict atom concentrations and nonequilibrium heat transfer within 10 percent of exact numerical solutions down to shock layer Reynolds numbers of roughly 100. The second and lower Reynolds number regime embraces fully viscous shock layer flow with appreciable nonadiabatic shock slip effects; here an analytical solution is given by treating the flow as nearly chemically frozen throughout. (Author).




Nonequilibrium Hypersonic Stagnation Flow at Low Reynolds Numbers


Book Description

An analysis of nonequilibrium-dissociated stagnation point flow on highly cooled blunt bodies in a hypersonic stream of air or diatomic gas at low Reynolds numbers is presented. An arbitrary atom recombination rate on the surface is allowed. With the use of a continuum, thin shock layer model, it is shown that for flight speeds on the order of 25,000 ft/sec or less, the problem can be broken down into two regimes, both of which can be treated analytically with good approximation. The first is a generalized nonequilibrium vorticity-interaction flow regime where most of the significant gas phase reaction effects occur, including the transition from recombination rate to dissociation rate-controlled behavior. The closed form solutions given for this regime predict atom concentrations and nonequilibrium heat transfer within 10 percent of exact numerical solutions down to shock layer Reynolds numbers of roughly 100. The second and lower Reynolds number regime embraces fully viscous shock layer flow with appreciable nonadiabatic shock slip effects; here an analytical solution is given by treating the flow as nearly chemically frozen throughout. (Author).




The Effect of Injection on Nonequilibrium Hypersonic Flow in the Vicinity of the Stagnation Point of a Body with Arbitrary Catalytic Activity of the Surface Including the Effects of Low Reynolds Numbers


Book Description

The purpose of the paper is to examine the influence of injection on the characteristics of a viscous shock layer that forms between a blunt body and the shock wave during hypersonic flow past the body under conditions of a nonequilibrium dissociation reaction in the gaseous phase and a nonequilibrium recombination reaction on the surface.




Nonequilibrium Blunt Body Flow of Air at Low Reynolds Number


Book Description

The report treats the nonequilibrium air flow around blunt bodies at high altitudes and reentry conditions. The inverse method is employed, and a reduced form of the Navier-Stokes equations is solved by finite difference techniques. Solutions are obtained for the flow around bodies which generate spherical, parabolic, and hyperbolic shock shapes. Body shapes closely resembling spherically blunted cones are obtained. The present solutions are compared with a very limited data base and other calculations. The results are shown to agree reasonably well with the data and the independent calculations.







The Blunt-body Problem in Hypersonic Flow at Low Reynolds Number


Book Description

Existing theoretical analyses and experimental results of the stagnation region in hypersonic flow at low Reynolds number are discussed. The approach based on the thin-shock-layer approxi mation is extended to study flow fields beyond the stagnation region as well as in the shock transition zone. The basic flow model consists of two adjoining thin layers: a shock-transition zone and a shock layer. The system of partial differential equations governing the high-density shock layer reduces to the parabolic type. The system governing the shock-transition zone reduces to ordinary differential equations similar to those of the one-dimensional shock wave. They give rise to a set of conservation relations across the shock, which account for the transport processes immediately behind the shock but do not involve details of shock-wave structure. With the modified Rankine-Hugoniot relations, the flow field in shock layer can be determined independ ently of the shock-transition zone. An essential feature of this formulation is that, when applied in conjunction with nonslip surface conditions, it always yields the appropriate surface heat transfer rate and skin friction (for unit accommo dation coefficients) in the free-molecule limit. (Author).




Experimental Heat Transfer to Hemispheres in Nonequilibrium Dissociated Hypersonic Flow with Surface Catalysis and Second-order Effects


Book Description

An experimental investigation of heat transfer to hemispheres with both catalytic and noncatalytic surfaces in nonequilibrium dissociated hypersonic nitrogen flow has been conducted. The wind tunnel flow conditions provided low Reynolds numbers, allowing the assumption of completely frozen shock and boundary layers while introducing the influences of second-order boundary layer effects such as vorticity interaction. The results for copper surfaces, when correlated using the stagnation point heat transfer equation of Rosner together with Lees' heat transfer distribution, are in good agreement with the secondorder theory of Cheng under the assumption of complete surface recombination of atoms. Reductions in heat transfer rate up to 30 percent were obtained with the use of noncatalytic coatings applied to the probes. (Author).




Hypersonic Flow Research


Book Description

Progress in Astronautics and Rocketry, Volume 7: Hypersonic Flow Research compiles papers presented at a conference on hypersonics held at the Massachusetts Institute of Technology in August 1961. This book discusses the low Reynolds number effects, chemical kinetics effects, inviscid flow calculations, and experimental techniques relating to the problems in acquiring an understanding of hypersonic flow. The structure and composition of hypersonic wakes with attendant complex chemical kinetic effects is only briefly mentioned. This text consists of five parts. Parts A to C comprise of theoretical papers on the problems of calculating flow fields at hypersonic speeds. The experimental techniques that are of immediate practical interest in view of the difficulty of flight testing are discussed in Parts D and E. This publication is beneficial to engineers involved in advanced design problems.




NASA Technical Note


Book Description




Theoretical Modelling of Aeroheating on Sharpened Noses Under Rarefied Gas Effects and Nonequilibrium Real Gas Effects


Book Description

Theoretical Modelling of Aeroheating on Sharpened Noses under Rarefied Gas Effects and Nonequilibrium Real Gas Effects employs a theoretical modeling method to study hypersonic flows and aeroheating on sharpened noses under rarefied gas effects and nonequilibrium real gas effects that are beyond the scope of traditional fluid mechanics. It reveals the nonlinear and nonequilibrium features, discusses the corresponding flow and heat transfer mechanisms, and ultimately establishes an analytical engineering theory framework for hypersonic rarefied and chemical nonequilibrium flows. The original analytical findings presented are not only of great academic significance, but also hold considerable potential for applications in engineering practice. The study explores a viable new approach, beyond the heavily relied-upon numerical methods and empirical formulas, to the present research field, which could be regarded as a successful implementation of the idea and methodology of the engineering sciences.