Click for next page ( 93


The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement



Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page 92
68 HYPERSONIC TECHNOLOGY FOR MILITARY APPLICATION APPENDIX B: Acronyms CDS carbide dispersion stabilized (alloys) CFD computational fluid dynamics DARPA Defense Advanced Research Projects Agency DOD Department of Defense HGV hypersonic glide vehicle HIP hot isostatic pressing HTTF high temperature test facility LDC liquid dynamic compaction MIPS millions of instructions per second NASA National Aeronautics and Space Administration NASP National Aerospace Plane ODS oxide dispersion stabilized (alloys) PIO pilot induced oscillations PNS parabolized Reynolds-averaged Navier-Stokes equations psf pounds per square foot RST rapidly solidified titanium TOGW take-off gross weight TPS thermal protection system ZAP zone anneal-processed

OCR for page 92
HYPERSONIC TECHNOLOGY FOR MILITARY APPLICATION APPENDIX C: Glossary 69 adiabatic Thermodynamic change in system without heat transfer across system boundary. In context of Gas Laws, possible to admit of exact adiabatic processes and visualize them happening; shockwave, though not isentropic, is not adiabatic in classical sense because thermodynamic changes are not reversible. fir- breathing Aspiring air, specifically aircraft propulsion system that sustains combustion of fuel with atmospheric oxygen. Imposes constraints on vehicle speed and height, but invariably offers longer range than rocket system for same vehicle size or mass. anisotropic Having properties, as conductivity, speed of transmission of light, etc., that vary according to the direction in which they are measured. bluntbody flows A blunt trailing edge or rear face of body cause turbulence immediately downstream, but main airflow cannot detect that body or airfoil has come to an end and thus continues to behave as if in passage over surface of greater length or chord. boundary layer Layer of fluid in vicinity of a bounding surface: e.g., layer of air surrounding a body moving through the atmosphere. Within the boundary layer fluid Notion is determined mainly by viscous forces, and molecular layer in contact with surface is assumed to be at rest with respect to that surface. Thickness of boundary layer is determined mainly by viscous forces, and molecular layer in contact with surface is assumed to be at rest with respect to that surface. Thickness of boundary layer is normally least to distance from surface to fluid layer having 99% of free- stream velocity. Boundary layer can be laminar or, downstream of transition point, turbulent. cold wall The condition of low model surface temperatures to allow more accurate aerodynamic testing in a hypersonic wind tunnel. creep Slow plastic deformation under prolonged constant load, greatly accelerated by high temperatures. cryogenic Operating at extremely low temperatures. diabetic process Process in thermodynamic system with transfer of heat across boundaries. drag Retarding force acting upon body in relative motion through field, parallel to direction of motion. Sum of all retarding forces acting on body, such as induced drag, profile drag. dynamic pressure Pressure of a fluid resulting from its motion when brought to rest on a surface, given by q = lpV2; in incompressible flow, difference between total pressure and static pressure.

OCR for page 92
70 HYPERSONIC TECHNOLOGY FOR MILITARY APPLICATION en A parameter used to correlate boundary layer transition; the faster by which disturbances grow before transition occurs. enthalpy Total energy (heat content) of system or substance~undergoing change from one stage to another under constant pressure, expressed as H = E + PV, where E is energy, P pressure, and V volume. flight envelope Curves of speed plotted against altitude or other variable defining performance limits and conditions within which equipment must work. flow fields Small regions within the physical flow plane, in each of which all flow properties, including velocity, direction, pressure, etc. are considered constant. free stream Fluid outside region affected by aircraft or other-body. hypersonic faster than Mach number 5. Knudsen number, Kn Mean free path divided by characteristic length of body. laminar boundary layer Comprise successive laminar layers, that adjacent to surface having zero relative velocity and successive layers adding velocity out to the free stream. laminar flow Fluid flow in which streamlines are invariant and maintain uniform separation with perfect non-turbulent sliding between layers. Lewis number Le = Pr (Prandtl)/Sc (Schmidt), used in hypersonics. lift 1. Total lifting force from a wing (component of resultant force along lift axis), aerostat envelope or other source excluding engine thrust. Normally, force supporting aircraft. 2. Any element of such lift, acting through particular point. Mach number, M Ratio of true airspeed to speed of sound in surrounding fluid (which varies as square root of absolute temperature). moment Turning effect about an axis; force multiplied by perpendicular distance from axis to force. monocoque Three-dimensional form, such as fuselage, having all strength in skin and immediate underlying frames and stringers, with no interior structure or bracing. Monte Carlo methods Use of random numbers to generate statistics on the behavior of estimators of an assumed set of structural equations. Navier-Stokes equations Basic set of equations for motion of body or flow parcel in viscous fluid. Nusselt number Non-dimensional parameter Nu = -qD/~5T where q is quantity of heat, D is typical length, ~ is thermal conductivity and [T is temperature difference. pitch Angular displacement (rotation) about lateral (OY) axis.

OCR for page 92
HYPERSONIC TECHNOLOGY FOR MILITARY APPLICATION pitching moment One causing pitch, measured as positive when nose-up or tail-heavy. 71 Prandtl number Ratio of momentum diffusivity to thermal diffusivitY. Pr = u Cal/) = vet where ~ is viscosity, Cp is specific heat at constant p, A is thermal conductivity, v is kinematic viscosity, and ox is angle of attack. pyrolysis Chemical decomposition by heating. q dynamic pressure ~,, ram Increase in pressure in forward-facing tube, duct, inlet, etc., as result of vehicle speed through atmosphere; if fluid flow were brought to rest in duct, pressure would be q, dynamic pressure. Hence ram inlet, ram pressure, ramjet, ram air, ram effect. ramjet Air-breathing jet engine similar to turbojet but without mechanical compressor or turbine; compression is accomplished entirely by ram and is thus sensitive to vehicle forward speed and non-existent at rest (hence ram cannot start from rest). Inefficient below Mach number 3 but extremely important for unmanned vehicles, especially in conjunction with rocket (.e.g., ramrocket). Also called athodyd, Lorin duct; not to be confused with pulsejet or resonant ducts. ramp Sharp-edged wedge with sloping wall forming inner wall of supersonic inlet duct to create oblique shocks and improve pressure recovery, especially at supersonic speeds; usually has variable geometry. regenerative cooling Use of cool incoming liquid, e.g., rocket engine propellant, to remove heat from hot hardware, e.g., rocket nozzle skirt and exit cone. Essential feature is that heat transfer is beneficial to both cooled item and coolant. Rex Reynolds number based on position along surface measured from start of boundary layer growth. Reynolds number Most important dimensionless coefficient used as indication of scale of fluid flow, and fundamental to all viscous fluids; R = pVl/p where p is density, V velocity, 1 a characteristic length (e.g., chord of wing) and ~ viscosity = Vl/v where v is kinematic viscosity. Expression is ratio of inertia to viscous forces. It shows, e.g., that for dimensionless similarity, model tests in tunnels should be run at pressures greater than atmospheric. Schmidt number Sc = p/pD, 2 where ~ is viscosity, p is density, and DO diffusion coefficient; ratio of viscous and mass diffusivity, or kinematic viscosity divided by mass diffusivity. scramjet Supersonic combustion ramjet; one in which flow through combustor itself is still supersonic. shock front The initial part of a shock wave in which the pressure rises from zero up to its peak value. The shock front is generally assumed to be infinitely thin and a mathematical discontinuity, but is actually of finite thickness. This front is not in equilibrium; it is a transition region between equilibrium conditions in the air ahead of the shock and the changed gas mixture behind it.

OCR for page 92
72 HYPERSONIC TECHNOLOGY FOR MILITARY APPLICATION shock layer In supersonic aerodynamics, the region between the shock front and the boundary layer; assumed to be an inviscid flow. Radiation from the shock layer to the nose cone of high speed missiles is one of the causes of skin heating. shock wave A surface or sheet of discontinuity set up in a supersonic field of flow through which the fluid undergoes a finite decrease in velocity accompanied by a marked increase in pressure, density, temperature, and entropy, as occurs, e.g., in a supersonic flow about a boov. sideslip Flight maneuver in which controls are deliberately crossed, e.g., to sideslip to left airplane is banked to left while right rudder is applied; result is not much change in track but flight path inclined downward, i.e. steady loss of height without significant change in airspeed and with longitudinal axis markedly displaced from flightpath. Angle of sideslip is angle between plane of symmetry and direction of motion (flightpath, or relative wind). Rate of sideslip is component of velocity along lateral axis. sloshing Gross oscillatory motion of liquid in tank sufficient to impose severe structural stress or affect vehicle trajectory. stagnation point Point on surface of body in viscous fluid flow (one facing upstream and one down) where fluid is at rest with respect to body, flow in boundary layer on each side of stagnation point being in opposite directions. stagnation temperature That at stagnation point, when all relative kinetic energy has been converted isentropically to heat. Stanton number Non-dimensional number defining heat transfer through a surface; St = -q/pVCpdT where q is total quantity of heat, p is density of fluid (e.g., air), V is relative velocity, Cp is specific heat at constant pressure and UT is recovery temperature minus wall temperature. static divergence The efflux per unit volume from a point. thermal fatigue Mechanical fatigue caused by stresses repeatedly imposed by thermal cycling (oscillation between low and high temperatures). thrust Force, especially that imparting propulsion. transitional flow A flow of fluid that is changing from laminar flow to turbulent flow. trim Angle between longitudinal axis (OX) and local horizontal, especially of airship, marine aircraft or seaplane float on water. {u rbulent flow Flow having turbulence superimposed on main movement, measured as velocity increments about all three axes expressed as fraction or percent of mean flow velocity. v iscosity Internal friction in fluid; property that enables fluid to generate tangential force and offer dissipative resistance to flow, defined as ratio of shear stress to strain; in air almost unaffected by pressure but increases with temperature.

OCR for page 92
HYPERSONIC TECHNOLOGY FOR MILITARY APPLICATION APPENDIX D: Dimensionless Groups in Fluid Mechanics Qualitative ratio Parameter Definition of effects Importance Reynolds number Re = pUL/p Inertia/Viscosity Always 73 Mach number Ma= U/a Flow speed/Sound speed Compressible flow Froude number Fr= U2/gL Inertia/Gravity Free-surface flow Weber number We = pU2L/T Inertia/Surface tension Free-surface flow Cavitation number Ca= p-pU/pU2 Pressure/Inertia Cavitation (Euler number) Prandtl number Pr = pcp/k Dissipation/Conduction Heat convection Eckert number Ec = U2/cpTo Kinetic energy/Enthalpy Dissipation Specific-heat ratio 7= cp/c',, Enthalpy/Internal energy Compressible flow Strouhal number St = wL/U Oscillation/Mean speed Oscillating flow Roughness ratio c/L Wall roughness/ Turbulent, rough walls Body length Grashof number Gr = ,B~TgL3p2/~2 Buoyancy/Viscosity Natural convection Temperature ratio TOO/To Wall temperature/ Heat transfer Stream temperature Pressure coefficient Cp = p_poO/IpU2 Static pressure/ Dynamic pressure Aerodynamics, hydrodynamics

OCR for page 92
74 HYPERSONIC TECHNOLOGY FOR MILITARY APPLICATION Parameter Lift coefficient Drag coefficient Lewis number Knudsen's number Stanton number Schmidt number p/pO Definition CL= F/IpU2A CD = D/ipU2A pcpu/p Molecular mean free path/ length h/cppv = (Cf/2)( 1 /PR)2/3 Qualitative ratio of effects Lift force/ Dynamic force Drag force/ Dynamic force Mass diffusion/ Energy diffusion Measure of continuum or Free molecular flow Reynolds analogy between friction and heat transfer Viscous to Diffusion ratio The only unusual parameter here is lo, which is a diffusion coefficient. Importance Aerodynamics, hydrodynamics Aerodynamics, hydrodynamics

OCR for page 92
HYPERSONIC TECHNOLOGY FOR MILITARY APPLICATION APPENDIX E: Letter to National Aerospace Plane Contractors Date: To: From: July 14, 1987 NASP Contractors AFSB Committee on Hypersonic Technology for Military Operations Subject: Approach Being Taken to Critical Technologies for NASP INTRODUCTION The National Research Council Air Force Studies Board has been requested by the Commander, Air Force Systems Command, to conduct a broad review of the status of technologies critical to hypersonic flight, and to assess the possible applications of hypersonic flight by the Air Force. More specifically, the task of the committee is to: 1) 3) 4) 5) develop an understanding of possible military applications of hypersonic flight. draw on the developing hypersonic technology base, including the evolving results of NASP Phase II, to assess the technical feasibility of realizing the potential applications. identify the technological needs for hypersonic flight. assess the research and development support requirements including availability of expertise, data bases, and tests facilities. provide technical advice to the command level on the research and development strategy of the NASP, including: a) the level of technical risk in a single-stage to orbit research vehicle, and strategies for risk reduction. by the research vehicle program approach to maximize the acquisition of knowledge in the most critical technical areas. 75