Development of a Mach 5 Nonequilibrium-Flow Wind Tunnel

Abstract

A small-scale Mach 5 blowdown wind tunnel has been developed to generate steady-state nonequilibrium flows. The wind tunnel uses transverse nanosecond pulse discharge, overlapped with transverse dc discharge, to load internal energy modes of N 2 and O 2 in plenum. The stable discharge is operated at high plenum pressures, at energy loadings of up to 0:1 eV=molecule in nitrogen, generating nonequilibrium nitrogen and airflows with run time of 5-10 s, translational/rotational temperature of T 0 300-400 K, and N 2 vibrational temperature of up to T V0 2000 K. Internal energy-mode disequilibrium is controlled by injecting O 2 , NO, H 2 , or CO 2 into the subsonic flow between the discharge and the nozzle throat. Flow over a cylinder model in a Mach 5 test section is visualized by schlieren imaging and NO planar laser-induced fluorescence imaging, using a burst-mode laser operated near 226 nm, at a pulse-repetition rate of 10-20 kHz. NO planar laser-induced fluorescence images on two single-line NOX; v 0 0 ! A; v 00 0 transitions are used to infer rotational temperature distributions in NO-seeded nitrogen flows in the supersonic section, with and without discharge. Single-line NO planar laser-induced fluorescence images on a NOX; v 0 1 ! A; v 00 1 transition are used to infer the NO vibrational temperature in a nitrogen Mach 5 flow excited by the discharge and seeded with NO. The results are compared to three-dimensional nonequilbrium flow modeling calculations, showing good agreement.

Nitrogen Vibrational Population Measurements in the Plenum of a Hypersonic Wind Tunnel

“…In the present work, the reduced electric field was estimated simply as the reduced voltage between the dc electrodes V-V 0 divided by the electrode gap and the number density, assuming 375 K gas temperature in the discharge. This is justified by our previous translational-rotational temperature measurements in the pulser-sustainer discharge at these conditions [4,5] from N 2 emission UV/visible spectroscopy, which yields temperature in the range T 350-400 K. Figure 15 shows essentially identical vibrational temperature behavior for all three pressures for E=n < 7 Td. For the 200 torr case, lower vibrational excitation is observed for E=n > 7 Td than that observed for the other two pressure cases, which remain in good agreement.…”

“…Additionally, as mentioned, the calculation for reduced electric field was performed with the assumption of spatial uniformity, and it is possible that the actual E=n at the measurement location is somewhat lower than the estimated value. A third factor, which was previously mentioned, is the discharge spatial nonuniformity with the visual intensity, and likely the energy deposition, being greater near the edges of the discharge than in the center [4,5] (see Fig. 16).…”

“…Figure 3 shows typical pulse voltage and current traces (top), as well as instantaneous power and coupled pulse energy traces (bottom), measured in a repetitively pulsed discharge in nitrogen at P 0 350 torr and 100 kHz [5], without dc electrodes present in the test section. The waveforms shown are for a pulse generated 0.1 s after the beginning of the pulse burst (i.e., for pulse number 10,000).…”

“…The experiments conducted for this study were performed in the plenum of a Mach 5 nonequilibrium flow tunnel, previously developed and described in detail [4,5]. Briefly, the laboratory-scale wind tunnel, a schematic of which is given in Fig.…”

“…This provides a significant incentive for the development and use of small-scale test facilities that are capable of recreating environments seen in the flow conditions of interest, and which lend themselves to development of optical diagnostics of nonequilibrium hypersonic flows. Our approach to generating a nonequilibrium hypersonic flow is to use a high-pressure low-temperature diffuse electric discharge sustained in the plenum of a small-scale Mach 5 wind tunnel to load internal energy modes of nitrogen and oxygen molecules [4,5]. A similar approach has been used previously to develop electrically excited gas dynamic lasers [6,7].…”