Showing papers on "Dynamic pressure published in 1974"

The cryogenic wind tunnel concept for high Reynolds number testing

Abstract: Theoretical considerations indicate that cooling the wind-tunnel test gas to cryogenic temperatures will provide a large increase in Reynolds number with no increase in dynamic pressure while reducing the tunnel drive-power requirements. Studies were made to determine the expected variations of Reynolds number and other parameters over wide ranges of Mach number, pressure, and temperature, with due regard to avoiding liquefaction. Practical operational procedures were developed in a low-speed cryogenic tunnel. Aerodynamic experiments in the facility demonstrated the theoretically predicted variations in Reynolds number and drive power. The continuous-flow-fan-driven tunnel is shown to be particularly well suited to take full advantage of operating at cryogenic temperatures.

Nonlinear Panel Response by a Monte Carlo Approach

Abstract: The vibration of clamped and simply supported elastic panels due to subsonic and supersonic turbulent boundary-layer flows is investigated by a Monte Carlo technique. The resulting generalized random forces are simulated numerically from boundary-layer turbulence spectra, and the response analysis is performed in the time domain. The mutual interaction between panel motion and external and/or internal airflow is included. Response studies are performed with respect to rms response, probability structure, peak distribution, threshold crossing and spectral density. The effect on the response statistics of in-plane loading, static pressure differential, and cavity pressure is investigated.

Simulation of flight test conditions in the langley pilot transonic cryogenic tunnel

Abstract: The theory and advantages of the cryogenic tunnel concept are briefly reviewed. The unique ability to vary temperature independently of pressure and Mach number allows, in addition to large reductions in model loads and tunnel power, the independent determination of Reynolds number, Mach number, and aeroelastic effects on the aerodynamic characteristics of the model. Various combinations of Reynolds number and dynamic pressure are established to represent accurately flight variations of aeroelastic deformation with altitude changes. The consequences of the thermal and caloric imperfections of the test gas under cryogenic conditions were examined and found to be insignificant for operating pressures up to 5 atm. The characteristics of the Langley pilot transonic cryogenic tunnel are described and the results of initial tunnel operation are presented. Tests of a two-dimensional airfoil at a Mach number of 0.85 show identical pressure distributions for a chord Reynolds number of 8,600,000 obtained first at a stagnation pressure of 4.91 atm at a stagnation temperature of 322.0 K and then at a stagnation pressure of 1.19 atm at a stagnation temperature of 116.5 K.

Gauge system for measuring air flow in ducts

Abstract: For use in measuring air velocity and pressure changes in a duct, a gauging system comprising a gauge including a vertically extending transparent tube within which a ball moves to a position corresponding to the pressure in the tube above and below the ball, a velocity scale and a pressure scale extending alongside the tube and increasing from their lower end to their upper end, a vertically extending transparent shell enclosing the tube, and one or more rigid tubes for connecting the lower end of the gauge tube to the interior of the duct to read total pressure or static pressure and a flexible tube for connecting the upper end of the shell to the interior of the duct to read static pressure. The rigid tube or tubes provide a distal end portion with an open end arranged to be pointed upstream or opposite to the direction of flow of air through the duct to read total pressure including velocity pressure and static pressure while the flexible tube provides a distal end portion with an open end and arranged to read the static pressure. The static pressure, therefore, pushes downwardly upon the ball while the total pressure pushes upwardly on the ball such that the static pressure is subtracted from the total pressure leaving velocity pressure which corresponds to velocity. The gauging system can simply be carried into a walk-in duct to read the air velocity therein without drilling or cutting access holes in the duct wall. The gauging system can be used to read pressure drop or increase across an item such as a coil or fan in a duct.

Numerical solutions for determining wave induced pressure distributions around buried pipelines

Abstract: Numerical models using both the finite difference and finite element technique are developed to simulate the interaction of a two-dimensional pipe-soil-wave system. The wave- induced pressure distribution in the soil region without an embedded pipe is first studied and solutions validated by comparing with existing analytical and experimental results. Numerical models are then used to solve the dynamic pressure distribution around buried pipes. Results are obtained for both a square pipe and a circular pipe and comparisons are made for different cases of input wave and soil parameters.

Simulation of Real-Gas Effects for Mars Entry

Abstract: The changes in aerodynamic characteristics due to real-gas effects associated with high speed flight (characterized by large shock density ratios) are primarily the result of changes in surface pressures acting on the forebody. The surface pressures are affected by a change in shock density ratio (real-gas effects) in two ways. First, the level of pressure at the stagnation point relative to freestream dynamic pressure is changed, and second, the distribution of surface pressure relative to stagnation-point pressure is changed. The density-ratio effect on the stagnation point pressure level can be estimated by considering the flow of a perfect gas about a blunt body.

Dynamic Passive Earth-Pressure Problem

Abstract: An incremental method is proposed for the study of stress and strain fields in a dynamic passive earth-pressure problem, where an initially vertical retaining wall is considered to translate or rotate with specified acceleration into a dry loose sand medium. The proposed incremental approach of this work enabled us to treat the problem of dynamic passive earth pressure as a mixed boundary value problem. At the beginning of the wall displacement, the dynamic normal earth pressure distribution is generally larger than the static pressure distribution. The dynamic mass ratio at the beginning of the wall displacement is shown not to depend on the amount of wall movement nor on the wall acceleration.

Flight-measured inlet pressure transients accompanying engine compressor surges on the F-111A airplane

Abstract: Two-F-111A airplanes were subjected to conditions that caused engine compressor surges and accompanying duct hammershock pressure transients. Flight speed ranged from Mach 0.71 to Mach 2.23, and altitude varied from approximately 3200 meters to 14,500 meters. A wide range of compressor pressure ratios was covered. Stabilized free-stream, engine, and duct conditions were established before each compressor surge. Dynamic pressure instrumentation at the compressor face and in the duct recorded the pressure transients associated with the surges. Hammershock pressures were analyzed with respect to the stabilized conditions preceding the compressor surges. The hammershock transients caused large pressure rises at the compressor face and in the duct. Hammershock pressure ratios at the compressor face were not affected by free-stream Mach number or altitude but were functions of engine variables, such as compressor pressure ratio. The maximum hammershock pressure ratio of approximately 1.83 occurred at a compressor pressure ratio of approximately 21.7.

A Stagnation Pressure Probe for Supersonic and Subsonic Flows

Abstract: The usefulness of a probe which can sense the absolute value of the stagnation pressure in supersonic flow has long been recognised. In the past such a probe has not been available and therefore it has been necessary to infer this fundamentally important flow property from measurements of other properties. This paper describes a probe which has been developed specifically to measure accurately the stagnation pressure of a supersonic gas stream. Measurements of the performance of the probe to date show that it is capable of measuring absolute stagnation pressure with an accuracy of 0.1 per cent in the Mach number range 1.5 to 2.1. No measurements have yet been made in the transonic range, but at low subsonic speeds the probe has demonstrated its ability to measure dynamic pressure within an accuracy of 0.1 per cent at a Mach number of approximately 0.13. The permissible range of misalignment in pitch and yaw before the pressure recovery begins to deteriorate are functions of free-stream Mach number and are usefully wide.