SP-4302 Adventures in Research: A History of Ames Research Center 1940-1965

 

PART II : A NEW WORLD OF SPEED : 1946-1958

1958

 

15

Facilities

 

RANGES AND SHOCK TUNNELS

 

[283] DURING 1958 the atmosphere-entry simulator and the pressure range were completed and put into operation. The simulator was one of the principal displays at the inspection in July. The main range, which had been completed late in 1957, was also put into service in 1958 but for a time was used principally for gun-improvement studies. Meanwhile the development work on shock tunnels was continuing. In the 10- by 14-Inch Tunnel Branch, a team comprising Bernie Cunningham, Fred Han-sen, Sam Kraus, and Charles Hermach was giving attention to a tunnel in which fixed models could be tested in a high-energy airflow for reasonably long (100-millisecond) periods of time. At the same time Tom Canning and his colleagues in the SSFF tunnel were developing a shock tunnel, capable of producing flows of modest speed (6000 fps) but relatively high density, for use in counterflow arrangement with a shock-driven light-gas gun. One such arrangement, called the pilot hypervelocity free-flight facility, was completed in 1958 and used for investigating the radiation from the glowing wakes of aerodynamically heated test bodies. Radiation studies of this kind were, indeed, the intended function of the facility.

The pilot hypersonic free-flight facility was a modest pioneering sort of device built "on a shoestring" at a cost of less than $30,000. It used a two-stage shock-driven light-gas gun, capable of launching small models at speeds of about 20,000 feet per second, and a shock tunnel that produced air (any gas) speeds of about 5500 feet per second. The relative speed was approximately 25,000 feet per second, which equaled the reentry speed of an earth satellite. The available Reynolds numbers also covered the satellite reentry conditions fairly well except in the low-altitude portion of the flight trajectory. Heating conditions as determined by stagnation temperatures at the nose of the reentry vehicle, and density or Reynolds number, were also fairly well represented in the new facility.

The nose-stagnation temperature of a model in a test facility is largely [284] determined by initial air temperature (preheating) and relative velocity. It may also be thought of in terms of the thermal-energy content of the air under nose-stagnation conditions. The thermal content of the air, in Btu's per pound, has been given the name "enthalpy." Thus for proper simulation of aerodynamic heating, the stagnation enthalpy and the air density or Reynolds number obtaining in flight must be reproduced in the test facility. What then were the flight-stagnation enthalpies and Reynolds numbers to be matched in the new test facilities at Ames? Approximate flight enthalpies for cases of particular interest are:

 

(1) Reentering ballistic missile warhead: 8,000 Btu/Ib
(2) Returning earth satellite: 14,000 Btu/Ib
(3) Returning lunar spacecraft: 25,000 Btu/Ib
(4) Returning planetary spacecraft: 50,000 Btu/Ib

 

Reynolds numbers for the same cases range up to nearly 100 million per foot for the returning planetary spacecraft and perhaps only a million or two for the returning earth satellite and lunar spacecraft.

The new pilot hypersonic free-flight facility provided the highest enthalpy yet attained in an Ames facility-about 13,000. The Reynolds numbers attainable under these conditions were 1 million or less. This performance was not bad, but clearly, for space research, facilities having higher ranges of both variables would be needed. In a comparison of test devices, it was apparent that a desired value of enthalpy could be achieved with less preheating of the air in a device in which the model itself was in motion than in a device in which the model was fixed. And, since preheating was always troublesome, it also was clear that the hypervelocity free-flight facility had a certain advantage over other test devices such as the arc-jet, the shock tunnel, and, quite definitely, the heat-transfer tunnel.

 

HEAT OR HELIUM

 

The new heat-transfer and low-density tunnels were now in operation but were not entirely satisfactory. The low-density tunnel, while useful, did not provide adequate simulation of aerodynamic heating, and the heat-transfer tunnel was beset by a multitude of operational problems arising in large part from the use of high preheating temperatures in a continuous-flow tunnel having a variable-geometry throat. The latter facility provided Glen Goodwin and his staff with some valuable, if painful, experience in windtunnel design. The low-density tunnel, on the other hand, had a fixed throat and was of the nonreturn, blowdown type; in it preheating of the air was quite feasible. To achieve such heating, Jack Stalder was in 1957-1958 experimenting with a pebble-bed heater. This was the pioneer application of pebble-bed heaters at Ames and as earlier noted, led to the use of such heating means in the new 3.5-foot hypersonic tunnel.

[285] The troubles that Goodwin had with his hot tunnel caused him to take an increased interest in helium tunnels such as had been proposed to, and turned down by, NACA management. Glen's interest in helium tunnels was shared by Al Eggers, and during 1958 each of them set about designing such a facility. As a result of this work, the construction of a 12- by 12-inch helium tunnel was proposed to NACA management and included in the appropriations request for fiscal year 1959. Congressional approval was obtained in the fall of 1958 and the detail design of the facility was begun The tunnel was to be located just north of the Unitary Plan facility. It would be of the unheated blowdown type designed to operate with fixed nozzles at Mach numbers of 10, 15, 20, and 25. The helium, stored under pressure in steel cylinders, would be released through the test section whence it would flow into evacuated, spherical recovery tanks.

Despite the intriguing qualities of helium tunnels, such facilities, as earlier noted, lacked the capability for realistically simulating reentry heating conditions. As this limitation was generally recognized, Ames research engineers maintained a keen interest in arc-jet developments. Arcjet development work at Ames had begun in 1956 and since then had been carried on at an increasing tempo but still at a fairly low level of effort. This work now, in view of space research needs, acquired a new urgency. The idea of the arc-heated wind tunnel (arcjet) was not new by any means, but the theory behind such devices and also the design techniques were in a rudimentary and very incomplete state. The development of an arc-jet in which the extreme aerothermodynamic conditions of space-flight reentry might successfully be simulated would clearly require years of theoretical and experimental investigation.

Although begun in 1956, the arc-jet project in 1958 seemed not to have progressed very far. The work in 1958 was being carried on by William Carlson, Carl Sorensen, James Jedlicka, Warren Winovich, Nick Vojvodich, and others. Initial specifications were established for an arc-jet facility of the type which was felt to be needed at Ames. The specifications were: 100-atmosphere pressure, 1-megawatt power input, 14,000-Btu-per-pound-energy (enthalpy) addition to the air. No arc-jets then available would come anywhere near meeting these specifications. It was up to Ames to develop its own unit. The work undertaken at this time led to the development of the Ames concentric-ring arc heater. In the operation of this heater, the position of the arc between the water-cooled ring electrodes was to be continuously moved by means of a rotating magnetic field to avoid excessive evaporation of the electrode material.

 

AEROPHYSICS FACILITY

 

It had been clear for some time that much basic research on the physics of gases and particles was needed to support the studies of hypervelocity.....

 


[
286]

Concentric-ring arc-jet.

Concentric-ring arc-jet.

 

....aerothermodynamics to which the Ames Laboratory was heavily committed. The required studies were now of such magnitude and complexity as to preclude their accomplishment with makeshift equipment Iocated in some odd corner of an existing building. A separate new laboratory facility would be required; and such a facility, it was felt, should be equipped with a variety of research instrumentation such as shock tubes, particle accelerators, a Van de Graaff generator, all ionized-gas tunnel, magnetohydrodynamics facilities and a host of smaller items. In the fiscal 1959 construction budget, which was prepared in 1958, such a facility was proposed. This budget item, called the hypervelocity research laboratory, was approved by the Congress and put under design in the fall of 1958. It was to be located immediately north of the Unitary Plan facility and adjacent to the new helium tunnel.

 

COMPUTING FACILITIES

 

Computing facilities at Ames were further augmented during 1958 and their uses expanded. A powerful 704 computer was leased from IBM to serve the needs of theoretical research. It was planned that any time remaining to the machine after performing its principal function would be devoted to off-line wind-tunnel-data reduction. A beginning was made during this period in the application of computer techniques to administrative accounting. The EAM (Electronic Accounting Machines) system used for this application involved a combination or a mechanical card sorter and an electronic computer.


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