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The nozzle in a hypersonic wind tunnel is generally subjected to a severe thermal environment. Several methods can be used to manage the energy absorbed by the nozzle, including backside cooling, film/transpiration cooling, and storing the energy in a heatsink fashion. The development of new alloys that retain strength at higher temperatures has increased the feasibility of the selflimiting heat-sink mode of operation. This paper discusses the development of a series of such alloys as well as the applications for which they have been designed. The most promising of these is an Ir-Zr alloy. A nozzle has been fabricated from this alloy. Nozzle survivability tests with this alloy are planned.

Arnold Engineering Development Center (AEDC) and the German Aerospace Institute (DLR) have conducted a cooperative program on operation and test technique development for high enthalpy shock tunnels. The AEDC Free-Piston Shock Tunnel (FPST) and the DLR High Enthalpy Gottingen (HEG) facility were used for complementary test programs. The two organizations individually and jointly analyzed data from these tests to assess and advance the state of their computational fluid dynamics capabilities. Several nonintrusive diagnostic techniques were employed at each facility resulting in new and improved diagnostic capabilities for each partner. This report explains the organization of the joint program reviews the operation of free-piston shock tunnels and presents the results of data acquisition and analysis from the test programs., "The original document contains color images"

Multiple experiments were conducted in the late 1980's and early 1990's to determine the effectiveness of transpiration and film cooling on the temperature control of an infrared (IR) seeker window during a missile's hypersonic flight. These efforts were made in support of the United States Army Space and Strategic Defense Command (USA SSDC) High-Endoatmospheric Defense Interceptor (HEDI) program. The experiments were designed as a series of complementary tests in several facilities that would provide the data necessary to predict window-cooling requirements. Recent emphasis on a similar missile system program, Atmospheric Interceptor Technology (AIT), has prompted a re- evaluation of the HEDI database of ground test data and led to new analysis of experimental results from one of the high-temperature facilities, Arnold Engineering Development Center's (AEDC) HR arcjet. While the HR test objective was oriented toward survivability issues and was conducted at a smaller scale (40 percent vs. 75 to 100 percent) and different geometry (2-D wedge vs. tetracone), window- cooling effectiveness results are in excellent agreement with other national facilities and the literature. Comparisons of the window-cooling data from AEDC Tunnels B and C, Calspan Hypersonic Shock Tunnel (HST) and HEDI facilities, AEDC/Naval Surface Warfare Center (NSWC) Tunnel 9, and AEDC HR are presented. In addition, the film-cooling effectiveness parameter, freestream turbulence, test article scale, and window-cooling breakpoint are discussed. Finally, new AEDC high-temperature facility capabilities are presented., Original contains color plates: All DTIC reproductions will be in black and white.

Issues relating to the use of arc-heated air for scramjet direct-connect testing are discussed. Direct- connect simulation issues are reviewed. The ability to satisfy simulation requirements is addressed. The effect of NO and copper contamination is discussed, as well as spatial and temporal flow fluctuations. It is concluded that arc heaters can provide a useful test environment in the simulated Mach number range, M(sim)= 6-10.

Arc heaters are required to provide the high pressure and temperature test conditions necessary to meet critical testing needs for propulsion, materials, and structures. Two configurations can produce the high power arc heater capability required: a single large arc or a multi-arc configuration based on manifolding a number of smaller heaters into a common plenum. Such multi-arc configurations can be a convenient route to high-power heaters (on the order of 200-300 MW), but at the cost of reduced performance because of additional wall cooling losses. A multi-arc configuration may be an effective way to improve flow uniformity of both enthalpy and pressure. The mixing of effluents of separate arc heaters in a single plenum may dampen flow-field fluctuations because oscillations in the individual arc units will probably be totally independent. Experiments were performed to assess the effect of manifolding arc heaters into a single plenum on flow quality and heater efficiency. A reduction in enthalpy of approximately 7 percent was attributed to the manifold. The reduction in enthalpy is caused by the additional wall losses in the manifold. Fluctuations in the flow were slightly better for the multi-arc configuration (compared to a single heater), primarily because of smaller fluctuations in the pressure. Heat flux fluctutations for the multi-arc system were nearly the same as for a single-arc heater.

The USAF/Arnold Engineering Development Center (AEDC) has undertaken an arc heater development program to develop a large, high-pressure, high-power arc heater capability. A large, state-of- the-art segmented arc heater (H3) is presently under development and is scheduled to be fully operational at chamber pressures up to 115 atm with a total power of 60 MW late 1995. The H3 arc heater is a 50-percent geometric scale- up of the existing Hi segmented arc heater and is designed to operate at 2.25 times the power of Hi. Future plans also include high-pressure (250 atm) segmented arc heater development, and development of a larger, higher power capability by manifolding several arc heaters into a single plenum or by developing a single very large arc heater. AEDO has also developed an extensive analytical capability to assist in the design and development of segmented arc heaters. This paper describes the present arc heater testing capabilities and development activities, along with future arc heater development plans., AIAA Aerospace Ground Testing Conference (18th), Colorado Springs, CO on Jun 20 - 23, 1994.

Analytical solutions of the integral equation of energy transport have so far been limited to a few simple geometries, one of which is the field with cylindrical symmetry - a good match with the geometry of modern high-pressure arc heaters, provided the electric discharge remains on the centerline of the heater. Unfortunately, it is known that the arc column in such devices undergoes substantial excursions from the centerline a large part of the time. To deal with the resulting strong asymmetries in temperature, the radiation transport was modeled using the differential (diffusion) approximation. This results in a partial differential equation which can be solved in multiple dimensions by the same methods that are used to solve the gasdynamic equations. The method has been verified by duplicating the one-dimensional formal integration results. Analysis of behavior of very hot gases requires the modification of the equations of motion by the addition of a radiant energy transfer term to the conservation of energy. Transport of radiant energy in a region of hot gas is described by the spatial and directional variation of the spectral radiation intensity function. This function is defined as the rate of flow of radiant energy of frequency v in the direction of the unit vector at a point specified per unit solid angle increment about the direction of propagation, and per unit increment of photon frequency about v. The spatial variation of Iv in a given direction is described by the radiative transfer equation (RTE) for a nonscattering gas., Original contains color plates: All DTIC and NTIS reproductions will be in black and white.