Hypersonic Technology for Military Application (1989) / Chapter Skim
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2 Technologies Relevant to Hypersonic Vehicles and Their Status
2 Technologies Relevant to Hypersonic Vehicles and Their Status
Pages 15-72
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From page 15... ...
While the resulting configurations are conceptually appealing, especially to the propulsion-oriented, they pose problems that, though not entirely new, are certainly more serious than for more conventional designs, in which the propulsive streamtube and fuselage and wing airflows are farther apart. Thus, in most if not all conceptual designs for hypersonic vehicles, the propulsion system is assumed to ingest the boundary layer flow that develops on the forebody.
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From page 16... ...
The ramp boundary layer and shock layer now accumulate more losses, higher static pressure, hotter and lower stagnation pressure air, and these are ingested into the engine. With no change in fuel flow, tile engine thrust and the pressure on the nozzle face HYPERSONIC TECHNOLOGY FOR MILITARY APPLICATION change and ~ strong pitching moment is developed.
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From page 19... ...
The importance of aerodynamicpropuisive integration for hypersonic vehicles has been recognized for many years, and has been highlighted over the last two by active participants in the NASP program and by advisory groups. But today there is more enthusiasm than integration.
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From page 20... ...
This flow field is quite complex due to the heat release, which is controlled by the molecular mixing process, and by the ramp boundary layer and bow shock layer that may be ingested by the engine. The heat release has a pro HYPERSONIC TECHNOLOGY FOR MILITARY APPLICATION pounced effect on the structure of the flow field which, in turn, strongly influences the mixing processes.
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From page 21... ...
When the engine ingests the ramp boundary layer and bow shock layer, the gas entering the combustor has a very non-uniform temperature distribution over its cross-section. As a consequence, the chemistry, which has a strong and non-linear temperature dependence, may vary even more violently over the cross-section.
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From page 22... ...
Though we have HYPERSONIC TECHNOLOGY FOR MILITARY APPLICATION some experience with this sort of problem, two important factors make the present situation unique. First, the transition to the scramjet mode lies in a Mach number range far outside our experience and where an error may be costly.
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From page 23... ...
The aerodynamic considerations require the treatment of real gases with full viscous effects applied to configurations that consist of blunt noses and leading edges on slim bodies with complex configurations that generate three-dimensional gradients and shock waves. The requirement is to predict, with reasonable accuracy, the following parameters, assuming similar inputs will be provided by the propulsion system: · Local pressures, heat transfer, and skin friction, on the surface of the entire vehicle, including the flow through the inlet.
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From page 24... ...
Conventional low Mach number use of the parameter Rex/M at values as low as 150 to about 300 has not been validated under the conditions of hypersonic flight or for complex flows. New attempts to use the parameter en are being studied by HYPERSONIC TECHNOLOGY FOR MILITARY APPLICATION NASAiLangley.
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From page 25... ...
2.3.3 Real Gas Effects in Complex Flows Inlets, bodies' fins, and wings, and their interactions, cause a combination of viscous effects, shock waves, and strong gradients with real gas effects. These must be understood to give detailed flowfields, such as for the combustor, where the local conditions and the constituents (state of the gas)
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From page 26... ...
This ancient problem could become a design driver at best and a potential show stopper at worst. 2.4.1 Physical Factors Hypersonic vehicles will demand sophisticated control for the engines, inlet, and guidance and control of the aircraft.
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From page 27... ...
One is a technology program focused on the thermal capabilities of sensors, cables, and connectors and the other is careful attention to the details of the thermal environment to which this type of equipment will be subjected. Hypersonic vehicles with their very high temperature will present an unusual requirement on control system sensors.
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From page 28... ...
Precise sideslip control is needed in essentially all hypersonic designs. 2.4.2.2 Integrated Propulsion/Flight Control and Guidance Speed control is sometimes essential to the trajectory adjustment control for hypersonic vehicles.
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From page 29... ...
(For example, relatively large effective time delays, partially due to structural mode filters, played a major role in the ALT 5 Shuttle PIO.) The net result for structural/slosh mode control is that the system may have to be "phase stabilized" in such a way that the net effective vehicle dynamics are appropriate for piloted control.
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From page 30... ...
Even worse, heat transfer rates will increase as leading edge radius decreases. Considering the shapes of projected hypersonic vehicles, a compound problem of very high temperature and no room for equipment such as the "Q ball" will further complicate the sensor problem even before redundancy is considered.
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From page 31... ...
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From page 33... ...
2.5 Materials for Hypersonic Vehicles 2.5.1 Introduction Structures for hypersonic vehicles must be lightweight, high-temperature resistant, inspectable, durable, and reliable. These requirements demand materials and concepts for structural design of hypersonic vehicles that are still in the emerging technology phase of development.
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From page 34... ...
HYPERSONIC TECHNOLOGY FOR MILITARY APPLICATION At high altitude, atmospheric oxygen begins to dissociate above Mach number 7, with both oxygen and nitrogen almost fully dissociated above about Mach number 15, and ionization above about Mach number 20. These real gas effects at the stagnation regions will require coatings to protect against oxidation, to form high emittance surfaces to lower surface temperatures, and to protect against erosion.
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From page 35... ...
Compared to the materials data required for subsonic aircraft, hypersonic aircraft materials data base requirements are much more extensive because of the need for thermal, chemical, oxidation and other data at elevated temperatures over specified time periods. 2.5.2 High Temperature Materials Potential system requirements dictate that the structural weight fraction of proposed hypersonic vehicles be much smaller than that of conventional subsonic aircraft.
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From page 36... ...
. Titanium aluminides have been proposed as matrix materials for SiC and other fiber-reinforced metal matrix composites, where the high temperature strength of the fibers offsets the rapid fall-off in strength of the titanium aluminide above 800° C
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From page 37... ...
1095 °C for-ODS (or MA) alloys TABLE 2-A Ti tan i up Al umi n i des Property Compari son
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From page 39... ...
The aim is to produce alloys capable of operation up to about 1000- 1 100° C while maintaining fabricability, formability, and while retaining oxidation resistance for thousands of hours, and exhibiting suitable strength, toughness, etc. Some properties of titanium aluminide materials are compared to conventional nickel base superalloys and titanium alloys in Table 2-A.
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From page 40... ...
The critical structural parameter is the interparticle spacing among dispersoids, making it HYPERSONIC TECHNOLOGY FOR MILITARY APPLICATION desirable to use exceedingly fine dispersoids (0.01 to 0.2 microns) to achieve high strength levels, long time stability at very high fractional melting temperatures, combined with demonstrated practical formability, useful ductility, and toughness.
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From page 41... ...
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From page 43... ...
2.5.2.4 Carbon-Carbon Composites and Ceramic Composite Materials For temperatures to 2200° C, carbon-carbon composite materials have shown excellent properties and performance on the shuttle leading edges and nose. New, improved manufacturing methods continue to be developed.
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From page 44... ...
Another aspect of the thermomechanical behavior at high temperatures that should be examined is the potential for stress relaxation by creep, particularly above 1650° C All carbon-carbon composites in hypersonic vehicles will encounter oxidizing environments, and the single most critical factor that could limit the use of such materials for structural applications is reliable oxidation protection.
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From page 45... ...
2.5.2.5 Processing Developments for Advanced Metallic Materials Since about 1950 a significant number of processing technologies have beers developed for incorporating fine refractory particulates into metallic matrixes. Recently, Benjamin and coworkers at the International Nickel Company, developed a mechanical alloying process for blending ultrafine Y2O3 into nickel base superalloys.
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From page 46... ...
. 2.5.3 Coatings Coatings will play a large role in insuring stability of the major structural materials at the high temperatures that hypersonic vehicles will be subjected to in flight at the high Mach numbers.
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From page 47... ...
2.6 The Structural Challenge The challenge confronting the structural designer of a hypersonic vehicle is reflected in the structural weight fraction, which is the weight of the whole structure divided by the take-off gross weight (TOGW)
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From page 48... ...
2.6.2 Structural Concepts Hypersonic vehicle performance depends intimately on such structural concepts as material choice, active/passive cooling, insulation, thermal protection, thermal/structural behavior, configuration, fabrication, and manufacturability. Vehicle structural concepts depend on the mission profile, e.g., a high-Mach cruiser with frequent use and short turn-around times will have different requirements than an orbital vehicle used frequently or a hypersonic reentry vehicle used only once.
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From page 49... ...
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From page 50... ...
Power Plant 3,941 0.016 523 0.002 Hydraulics 2,293 0.009 2,689 0.009 Electrical 4,041 0.017 2,683 0.009 Electronics 5,063 0.021 2,871 0.009 Furnishings 2,130 0.009 5,017 0.016 Air Conditioning 3,649 0.015 2,537 0.008 Thermal Protecti on 27,154 0.112 0.000 Crew 1,252 0.005 2,756 0.009 Fuel 23,856 0.099 111,480 0.354 Payload 60,000 0.249 70,000 0.222 J TOGW 241r379 1.000 315,135 1.000 TABLE 2-B Summary Weight Statements for Shuttle Orbiter and C-141
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From page 51... ...
Presumably the structural concepts developed are designed to realistic criteria, ultralight, temperature resistant, and durable. The next iog,ical step to advance a technology toward use as structural hardware is often discounted This step is fabrication or demonstration of manufacturability Very often, high technology en~leas~ors (such as the development of hypersonic vehicles)
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From page 52... ...
2.6.4 Status of Structural Concepts for Hypersonic Vehicles The NASP program has an aggressive Technology Maturation Plan to develop the technology base to design an experimental hypersonic X-plane. Prior to this NASP program, hypersonic technology base development had been spotty at best for 20 years with the exception of technology for reentry vehicles and the shuttle orbiter.
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From page 54... ...
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From page 55... ...
Obviously, if a material were available that had a coefficient of thermal expansion comparable to pyrex glass, and had elevated temperature strength properties comparable to those of 7075-T6 at normal temperatures, then the thermal problem would be trivial. Strength properties are important but such factors as corrosion resistance, susceptibility to thermal stresses, maturity of the manufacturing infrastructure to translate materials into structural forms and availability are of equal significance.
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From page 56... ...
Thus, there is also a thermal as well as a momentum boundary layer within which convection, conduction, and dissipation are balanced. HYPERSONIC TECHNOLOGY FOR MILITARY APPLICATION Two parameters of chief interest to the structural designer are the recovery factor and the heat transfer coefficient.
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From page 57... ...
So in this new field, it is again the structural designer who needs intimate knowledge of the origin and transfer of thermal energy in the boundary layer. 2.6.5.3 The Temperature Distribution in the Structure All three basic heat-transfer processes: convection, conduction, and radiation, are present in the aircraft temperature distribution problem.
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From page 58... ...
These result from extensive calculations under a number of critical conditions to which all other conditions are compared. HYPERSONIC TECHNOLOGY FOR MILITARY APPLICATION These critical conditions are either obviously worse than others or have been shown from experience to be the most severe.
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From page 59... ...
2.7 Role of Computational Fluid Dynamics Computational fluid dynamics (CFD) has become the principal tool for aerodynamic and propulsion-flow design of hypersonic vehicles.
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From page 60... ...
In consequence, the potential overall ability HYPERSONIC TECHNOLOGY FOR MILITARY APPLICATION of computers to simulate the proper thermodynamic and chemical aspects of hypersonic flight, while providing extraordinarily detailed information, has made it apparent that CFD continues to be essential for the design of hypersonic vehicles. We must note, however, that some level of physical approximation will be required to bring the numerical problem within practical computational capabilities.
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From page 61... ...
2.7.1.1 External Aerodynamics Computational fluid dynamics codes for this type of flow are the most advanced. With present supercomputers and codes, we can make 3-D computations of aerodynamic and heating parameters using the Reynolds-averaged Navier-Stokes equations for hypersonic flow over fuselage-wing-tail configurations, provided we know the location of boundary layer transition.
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From page 62... ...
2.7.1.4 Nozzle Flows In the expansion of combustion products through a nozzle, or a partly wall-bounded nozzle, reaction-rate chemistry is essential to the flow HYPERSONIC TECHNOLOGY FOR MILITARY APPLICATION computation. Currently 2-D reactionrate codes are used to compute nozzle exhaust expanding into ambient air, but 3-D reaction-rate codes for an expansion partly over the surface of a vehicle, and partly into a vehicle-dependent external aerodynamic flow, do not yet exist, although they are under development.
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From page 63... ...
The potential future importance of DNST to the Air Force is great, since it would largely overcome most of the present limitations of CFD. Such a capability would provide a large increase in the effectiveness of CFD applications to the design of aircraft and turbine engines as well as hypersonic vehicles.
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From page 64... ...
Consequently, flight test programs are needed for components of hypersonic air-breathing vehicles that cannot be adequately tested in ground facilities, for validation of concepts, and proof of CFD codes. Such testing HYPERSONIC TECHNOLOGY FOR MILITARY APPLICATION represents an extension of the ground test concept and is complementary to, not a substitute for complete systems ground testing.
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From page 66... ...
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From page 67... ...
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From page 69... ...
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From page 71... ...
Although a steeper rate of ascent probably would have to be followed above Mach number 12 because of temperature limitations on materials, Reynolds numbers of the order of 10 to 20 million can be expected up to above Mach number 20. For free stream Mach numbers above about 10, test requirements become even 51 more severe for slender vehicles because Mach number, free flight Reynolds number, and full enthalpy must be reproduced in a single test facility as real gas effects become important.
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From page 72... ...
HYPERSONIC TECHNOLOGY FOR MILITARY APPLICATION Of these high Re facilities only the Calspan shock tunnels are able to produce free flight total temperatures above Mach 10, and only the 96-in. shock tunnel approaches total temperatures for a Mach number well in the teens.
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