Engineering topics

Blackwell, Harvel E.

Publications and source records attributed to Blackwell, Harvel E..

4 records

NASA NTRS1992

Measured rotational and vibrational temperature differences in arc jet shock layers

Shock-layer-radiation emission spectra from the first negative system of the nitrogen molecular ion N2(+) are analyzed over the wavelength region between 370 and 430 nm. The shock layer is produced by a blunt body placed in the expanded flow from an arc heater employing either pure nitrogen or a nitrogen-oxygen air mixture. A rotational temperature is obtained from analysis of (0,1) band emission from N2(+). Vibrational temperatures are extracted from population distributions obtained through spectral fitting of the N2(+) (B-X) band sequences. Rotational temperatures up to 9500 K near the front of the shocks are determined for different energy and flow conditions. The rotational temperatures are found to be lower than those obtained for vibration confirming previous measurements and contrary to expectation based on theory.

Blackwell, Harvel E.↗

NASA NTRS1989

Nonequilibrium shock layer temperature profiles from arc jet radiation measurements

Shock layer temperature profiles are obtained through analysis of radiation from shock layers produced by a blunt body inserted in arc jet flow. Spectral measurements have been made in a nitrogen flow of 54.4 gm/s at an enthalpy of 8.72 MJ/kg. Vibrational temperatures for N2+ are obtained by matching spectral regions from arc jet spectra with spectra generated using the NEQAIR code. Temperature profiles obtained from the radiation layers show a vibrational temperature higher than the rotational temperature near the front of the shock and both temperatures decrease as the flow approaches the body. The spectral measurements are made and analysis completed for four distances, from the surface of the blunt body. The corresponding shock layer thickness is approximately 3.6 cm. Although the shock layer appears to be in thermal nonequilibrium, the measured rotational temperature approaches the single temperature results of viscous shock layer calculations at this test condition.

Blackwell, Harvel E.↗

NASA NTRS1989

Vibrational temperature from measurements of N2 and N2(+) shock layer radiation

Measurements of the vibrational temperature in a shock layer produced by a cylindrical blunt body in an arc jet nitrogen flow are made for both the neutral molecule and the molecular ion. Spectra were obtained at two locations in the shock layer produced by a 20-cm long cylindrical blunt body inserted in the arc jet conical flow. The technique used for determining the temperatures from the spectral radiation involves obtaining ratios of integrated intensities for certain spectral regions of the measured spectrum and making a comparison with computed ratios as a function of temperature for the same spectral regions. The technique is difficult to apply due to radiation overlapping bands from other species. However, using a trial and error procedure, the vibrational and rotational temperatures at the two locations are inferred. The results indicate that the shock layer is significantly out of thermal equilibrium.

Blackwell, Harvel E.↗

NASA NTRS1987

Spectral determination of nitrogen vibrational temperatures

A technique for determining the vibrational temperature of nitrogen molecules is found from the emission of the N2 first positive spectrum. The technique involves calculating wavelength integrals of portions of the emission spectrum associated with transitions from the ststes B3Pi(g)(v-prime) to A3 Sigma(u +)(v-double prime) where Delta = 2, 3, etc. Ratios of the integrated intensities are then correlated with vibrational temperature. The dependence of the technique on rotational temperature is considered and less dependence is obtained if the overlap between Delta v-regions is accounted for. The technique is applied to the shock layer of a blunt body in an arc jet flow. The N2(1+) spectrum is measured in the shock layer to obtain the intensity integral ratios. From these ratios estimates of the vibrational temperature are found from the correlation which agree quite well with calculated temperatures in the shock layer flow.

Blackwell, Harvel E.↗