Proposed Vertical Expansion Tunnel

It is proposed that the adverse effects from secondary diaphragm rupture in an expansion tunnel may be reduced or eliminated by orienting the tunnel vertically, matching the test gas pressure and the accelerator gas pressure, and initially separating the test gas from the accelerator gas by density stratification. This proposed configuration is termed the vertical expansion tunnel. Two benefits are 1) the removal of the diaphragm particulates in the test gas after its rupture, and 2) the elimination of the wave system that is a result of a real secondary diaphragm having a finite mass and thickness. An inviscid perfect-gas analysis and quasi-one-dimensional Euler computations are performed to find the available effective reservoir conditions (pressure and mass specific enthalpy) and useful test time in a vertical expansion tunnel for comparison to a conventional expansion tunnel and a reflected-shock tunnel. The maximum effective reservoir conditions of the vertical expansion tunnel are higher than the reflected-shock tunnel but lower than the expansion tunnel. The useful test time in the vertical expansion tunnel is slightly longer than the expansion tunnel but shorter than the reflected-shock tunnel. If some sacrifice of the effective reservoir conditions can be made, the vertical expansion tunnel could be used in hypervelocity ground testing without the problems associated with secondary diaphragm rupture

Experimental Investigation of Nozzle/Plume Aerodynamics at Hypersonic Speeds

The work performed by D. W. Bogdanoff and J.-L. Cambier during the period of 1 Feb. - 31 Oct. 1992 is presented. The following topics are discussed: (1) improvement in the operation of the facility; (2) the wedge model; (3) calibration of the new test section; (4) combustor model; (5) hydrogen fuel system for combustor model; (6) three inch calibration/development tunnel; (7) shock tunnel unsteady flow; (8) pulse detonation wave engine; (9) DCAF flow simulation; (10) high temperature shock layer simulation; and (11) the one dimensional Godunov CFD code

Superorbital expansion tube operation: estimates of flow conditions via numerical simulation

Two new operating conditions of the X3 superorbital expansion tube are studied experimentally and numerically. A two-stage numerical simulation is used to model the flow processes within the whole facility, from the compressed driver gas, through the initial shock-processing of the test gas and then through the unsteady expansion process to the final test flow state. Experimental measurements provide static pressure histories at particular points along the shock and acceleration tubes while the numerical simulations provide complementary information on gas density, temperature and composition. Operating condition properties such as shock speed are both observed in the experiment and produced as a result of the simulation are used to check the reliability of the numerical simulations

Incident shock-wave characteristics in air, argon, carbon dioxide, and helium in a shock tube with unheated helium driver

Incident shock-wave velocities were measured in the Langley 6-inch expansion tube, operated as a shock tube, with air, argon, carbon dioxide, and helium as test gases. Unheated helium was used as the driver gas and most data were obtained at pressures of approximately 34 and 54 MN/sq m. A range of pressure ratio across the diaphragm was obtained by varying the quiescent test-gas pressure, for a given driver pressure, from 0.0276 to 34.5 kN/sq m. Single- and double-diaphragm modes of operation were employed and diaphragms of various materials tested. Shock velocity was determined from microwave interferometer measurements, response of pressure transducers positioned along interferometer measurements, response of pressure transducers positioned along the driven section (time-of-arrival gages), and to a lesser extent, measured tube-wall pressure. Velocities obtained from these methods are compared and limitations of the methods discussed. The present results are compared with theory and the effects of diaphragm mode (single or double diaphragm), diaphragm material, heating of the driver gas upon pressurization of the driver section, diaphragm opening time, interface mixing, and two-dimensional (nonplanar) flow are discussed

Description and initial operating performance of the Langley 6-inch expansion tube using heated helium driver gas

A general description of the Langley 6-inch expansion tube is presented along with discussion of the basic components, internal resistance heater, arc-discharge assemblies, instrumentation, and operating procedure. Preliminary results using unheated and resistance-heated helium as the driver gas are presented. The driver-gas pressure ranged from approximately 17 to 59 MPa and its temperature ranged from 300 to 510 K. Interface velocities of approximately 3.8 to 6.7 km/sec were generated between the test gas and the acceleration gas using air as the test gas and helium as the acceleration gas. Test flow quality and comparison of measured and predicted expansion-tube flow quantities are discussed

Performance considerations for expansion tube operation with a shock-heated secondary driver

This paper reports on a study examining operation of a shock-heated secondary driver across the entire operating envelope of a free-piston driven expansion tube. It is found that the secondary driver operating characteristics depend significantly on the specific characteristics of the flow condition. Key trends and characteristics are identified, and theoretical concepts are validated by numerical analysis and experiment