Theoretical study of nonadiabatic boundary-layer stabilization times in a cryogenic wind tunnel for typical stainless steel wing and fuselage models

The time varying effect of nonadiabatic wall conditions on boundary layer properties was studied for a two dimensional wing section and an axisymmetric fuselage. The wing and fuselage sections are representative of the wing root chord and fuselage of a typical transport model for the National Transonic Facility. The analysis was made with a solid wing and three fuselage configurations (one solid and two hollow with varying skin thicknesses) all made from AISI type 310S stainless steel. The displacement thickness and local skin friction were investigated at a station on the model in terms of the time required for these two boundary layer properties to reach an adiabatic wall condition after a 50 K step change in total temperature. The analysis was made for a free stream Mach number of 0.85, a total temperature of 117 K, and stagnation pressures of 2, 6, and 9 atm

A theoretical analysis of simulated transonic boundary layers in cryogenic-nitrogen wind tunnels

A theoretical analysis was made to determine the real gas effects on simulation of transonic boundary layers in wind tunnels with cryogenic nitrogen as the test gas. The analysis included laminar and turbulent flat plate boundary layers and turbulent boundary layers on a two dimensional airfoil. The results indicate that boundary layers in such wind tunnels should not be substantially different from ideal gas boundary layers at standard conditions. At a pressure of 9.0 atm, two separate effects produce deviations of real gas values from ideal gas values which are in the opposite direction from deviations at 1.0 atm and are of the same insignificant order of magnitude. Results also show that nonadiabatic boundary layers should be adequately simulated if the enthalpy ratio is the correlating parameter rather than the temperature ratio

Image tube

An optical image is projected onto a planar surface of a photocathode that derives an electron beam replica of the image. A target electrode displaced relative to the photocathode so that it does not obstruct the optical image includes a planar surface for receiving and deriving an accurate replica of the electron beam image. The two planar surfaces are parallel. The electron beam image is focused on the target electrode by providing throughout a region that extends between the planar surfaces of the photocathode and receiving electrode, constant homogeneous dc electric and magnetic fields. The electric field extends in a direction perpendicular to the planar surfaces while the magnetic field extends along a straight line that intersects the photocathode and target electrode at an acute angle

A magnetically focused image tube employing an opaque photocathode

Image converter has been developed which uses opaque photocathode for improved efficiency. Device is easier to fabricate than previous semi-transparent photocathode converters and uses compounds from Groups 3-5 that are responsive to wave-lengths between ultraviolet (approximately 100 nm) and near infrared region (approximately 1000 nm)

Dynamic measurement of total temperature, pressure and velocity in the Langley 0.3-meter transonic cryogenic tunnel

There is theoretical and experimental evidence which indicates that a sudden or step change in the rate at which the liquid nitrogen is injected into the circuit of a cryogenic wind tunnel can cause a temperature front in the flow for several tunnel circuit times. A temperature front, which occurs at intervals equal to the circuit time, is a sudden increase or decrease in the temperature of the flow followed by a nearly constant temperature. Since these fronts can have an effect on the control of the tunnel as well as the time required to establish steady flow conditions in the test section of cryogenic wind tunnel, tests were conducted in the settling chamber in the Langley 0.3-meter Transonic Cryogenic Tunnel (0.3-m TCT) in which high response instrumentation was used to measure the possible existence of these temperature fronts. Three different techniques were used to suddenly change the rate of liquid nitrogen being injected into the tunnel and the results from these three types of tests showed that temperature fronts do not appear to be present in the 0.3-m TCT. Also included are the velocity and pressure fluctuations measured in the settling chamber downstream of the screens and the associated power spectra

Imaging and quantum efficiency measurement of chromium emitters in diamond

We present direct imaging of the emission pattern of individual chromium-based single photon emitters in diamond and measure their quantum efficiency. By imaging the excited state transition dipole intensity distribution in the back focal plane of high numerical aperture objective, we determined that the emission dipole is oriented nearly orthogonal to the diamond-air interface. Employing ion implantation techniques, the emitters were engineered with various proximities from the diamond-air interface. By comparing the decay rates from the single chromium emitters at different depths in the diamond crystal, an average quantum efficiency of 28% was measured.Comment: 11 pages and 4 figure

Hydrogen refinement during solid phase epitaxy of buried amorphous silicon layers

The effect of hydrogen on the kinetics of solid phase epitaxy (SPE) have been studied in buried amorphous Si layers. The crystallization rate of the front amorphous/crystalline (a/c) interface is monitored with time resolved reflectivity.Secondary ion mass spectrometry(SIMS) is used to examine H implanted profiles at selected stages of the anneals. The H retardation of the SPE rate is determined up to a H concentration of 2.3×10²⁰ cm¯³ where the SPE rate decreases by 80%. Numerical simulations are performed to model the H diffusion, the moving a/c interfaces and the refinement of the H profile at these interfaces. Despite the high H concentration involved, a simple Fickian diffusion model results in good agreement with the SIMS data. The segregation coefficient is estimated to be 0.07 at 575 °C. A significant fraction of the H escapes from the a-Si layer during SPE especially once the two a/c interfaces meet which is signified by the lack of H-related voids after a subsequent high temperature anneal.This research was supported by a grant from the Australian Research Council

A parametric study of effect of forebody shape on flow angularity at Mach 8

Flow angularity and static pressure measurements have been made on the lower surface of nine forebody models that simulate the bottom forward surface of a hypersonic aircraft. Measurements were made in an area of the forebody that represents the location of an inlet of a scramjet engine. A parametric variation of the forebody surface investigated the effect of: (1) spanwise curvature; (2) longitudinal curvature; and (3) planform shape on both flow angularity and static pressure distribution. Results of each of the three parametric variations of geometry were compared to those for the same flat delta forebody. Spanwise curvature results showed that a concave shape and the flat delta had the lowest flow angularity and lowest rate of increase in flow angularity with angle of attack. Longitudinal curvature results showed a convex surface to give the better flow at the higher angles of attack. The better of the two planform shapes tested was a convex elliptical shape. Limited flow field calculations were made at angles of attack using a three dimensional, method-of-characteristics program. In general, at all angles of attack there was agreement between data and theory