: Experimental measurements of convective stagnation point heat transfer in partially ionized air at stimulated flight velocities up to 55,000 fps are presented. Stagnation point heat transfer rates were measured in an arc-driven shock tube with calorimetric heat transfer gages, either coated with silicon-monoxide films or uncoated. The data are compared to theoretical predictions made with a simple binary diffusion model of partially ionized diatomic gas, nitrogen, whose transport properties were estimated from measured and calculated cross-section data. Stagnation point heat transfer rates calculated from this model for both a frozen and an equilibrium boundary layer, as well as equilibrium boundary layer results from other available calculations using more elaborate models of air, are compared to the data. It is concluded that the transport properties of air up to 15,000 K are known to reasonable accuracy and that heat conduction by electrons does not present a serious engineering problem for flight velocities up to 50,000 fps.

https://apps.dtic.mil/sti/pdfs/AD0406269.pdf

Stagnation point heat transfer measurements in partially ionized air

The laminar boundary layer behind a moving shock is studied. The major objective is to obtain improved correlation formulas (valid for large W, where W is the density ratio across the shock) and to simplify the procedure for obtaining boundary‐layer parameters. Numerical solutions for shear, heat transfer, and boundary‐layer thicknesses are presented for 1 ≤ W ≤ ∞, σ = 0.67, 0.72, and 1.0 (σ is the Prandtl number) assuming constant ρμ (ρ is the density and μ, the viscosity) and an ideal gas. Correlation formulas are obtained which agree with these numerical results to within fractions of a percent. Approximate corrections for variable ρμ and real‐gas effects are then introduced. Charts and tables are presented which describe boundary layers in air (Ms ≤ 22) and argon (Ms ≤ 10).

Correlation Formulas for Laminar Shock Tube Boundary Layer

A study of shock tube operation with free-piston compression of the driver gas is presented. It is shown theoretically and experimentally that shock Mach numbers exceeding 30 in air may be obtained with an apparatus of moderate size. The operating limitations imposed by the maximum pressures allowed in the apparatus, by the ratio of the volume of the shock tube to the volume of the compression tube, and by the maximum pressure available for driving the piston are all explored theoretically. The compression process is studied experimentally, and results for three different compression tubes are used to indicate empirical rules for maximising the efficiency of the compression process. Streak photographs of the movement of the luminous gas behind the shock wave in a 1 in diameter shock tube are used to demonstrate the quality of the shock-wave motion produced.

The Free-Piston Shock Tube

A spectroscopic technique is described for measuring nonequilibrium shock front rotational, vibrational and electronic temperatures. This method uses a triple channel monochromator which is able to resolve the vibrational structure of diatomic molecular radiation, and a monitor channel to observe an electronic transition composed of many vibrational transitions. Measurements are made on incident nitrogen shock waves by observing the Δv = +1 sequence of the N 2 + (1-) and N 2 (1+) systems. As well as giving nonequilibrium temperature results, this experiment has given equilibrium radiation intensities which indicate an f number at the 0, 0 transition of 0·035.

/pdf/nonequilibrium-shock-front-rotational-vibrational-and-3k4wvg7473.pdf

Nonequilibrium shock front rotational, vibrational and electronic temperature measurements

The admittance of a waveguide-fed rectangular aperture under an inhomogeneous plasma is derived and experimentally verified. For both flowing and stationary inhomogeneoas plasmas, the agreement is at least as accurate as presently available plasma diagnostic techniques will allow. It is shown that there is a clear separation of the dependence of aperture-admittance properties upon plasma properties, such as electron density, profile shape and collision frequency, over two to three decades of peak electron density, change. The collision frequency primarily affects the aperture conductance, particularly for critical and overdense plasmas. The profile shape, i.e., a boundary layer, primarily affects the aperture susceptance.

The Input Admittance of a Rectangular Waveguide-Fed Aperture Under an Inhomogeneous Plasma: Theory and Experiment

A shock tube has been developed capable of producing a gas sample of known conditions by shocks with velocities as high as 43 000 ft/sec. The driver of this shock tube employs a capacitor bank which discharges electrical energy into helium, heating the helium to temperatures of 10 000–20 000 °K, and raising the pressure to 10 000–20 000 psi. The high‐pressure bursts the scribed diaphragm and the resulting shock wave propagates into the test gas. Diagnostic techniques have been employed to investigate the resulting hot gas sample. The growth of this sample has been observed optically and correlations have been achieved with theoretical calculations. The observed radiation has been compared with and can be used to extend the known radiative properties of high temperature air. Time‐resolved luminous pictures and spectra have also been taken to show the purity of the test gas. The speed and attenuation of the shock front have been measured. The observed operation of this shock tube has been compared with theoretical predictions, and although no precise correlation can be made, the driver gas energy transfer and losses in the shock tube boundary layer can be accounted for.

Electric Arc-Driven Shock Tube

: Shock tubes were developed capable of producing a gas sample of known conditions at velocities as high as 43,000 ft/sec. The driver of these shock tubes employs a capacitor bank which discharges electrical energy into helium, heating the helium to temperatures of 10,000 - 20,000 K, and raising the pressure to 10,000 - 20,000 psi. The high pressure bursts the scribed diaphragm and the resulting shock wave propagates into the test gas. Extensive diagnostic techniques were employed in the resulting hot gas samples. The growth of this sample was observed optically, and correlations were achieved with theoretical calculations. The observed radiation was compared with and can be used to extend the known radiative properties of high-temperature air. Time-resolved luminous pictures and spectra were also taken to show the purity of the test gas. The speed and attenuation of the shock front were measured. The observed operation of this shock tube was compared to theoretical predictions, and although no precise correlation can be made, the driver gas energy transfer and losses in the shock tube boundary layer can be accounted for. (Author)

Electric shock tube for high velocity simulation

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Electric Arc-Driven Shock Tube

Electric shock tube for high velocity simulation