Total pressure

About: Total pressure is a research topic. Over the lifetime, 5199 publications have been published within this topic receiving 66658 citations.

Studies of hypervelocity firings into mixtures of hydrogen with air or with oxygen

Abstract: Plastic spheres, of 9 mm diameter, were fired at velocities of 1500–3000 m/sec into mixtures of hydrogen with air or oxygen. High-speed shadow and schlieren pictures gave good results concerning the phenomena before and behind the missile. Most experiments were made with a stoichiometric H 2 /air mixture at 0.55 atm. At firing velocities higher than the detonation velocity, a steady combustion front is established and at lower velocities instabilities in the form of oscillations appear. A quantitative study of the frequencies, shock pressures, and stagnation temperatures associated with the missile velocities, showed that the reciprocal frequency, or period of oscillation, is equal to the induction time for self-ignition. Similar results were obtained with H 2 /air mixtures with a twofold partial pressure of H 2 at a total pressure of 0.72 atm. However, frequencies did not vary with stagnation temperatures (and, hence, induction times) for a stoichiometric H 2 /O 2 mixture at 0.24 atm. Probably, these are acoustic oscillations with no relation to induction time. Photographs also were taken some distance behind the missle, when it had already passed the observation field. These pictures show a horizontal combustion-gas column, with a shock waveformed by propellant gases emitted by the gun muzzle. By taking two pictures, one over the other, with a definite delay, the shock-wave velocity in the column is determined as v =950–1200 m/sec. By considering the intensity of secondary shock waves in the ambient gas, the sound velocity in the combustion gas column is estimated from the shock velocity. This value allows one to calculate, approximately, the temperature of the combustion gas as T =1100°–1200°K for H 2 -air and H 2 −O 2 mixtures. However, experiments with stoichiometric H 2 −O 2 mixtures showed the development of a detonation wave along the combustion-gas column, with a detonation velocity D ≈2000 m/sec. These findings demonstrate that the combustion reaction, before and around the missile, is rather incomplete. A calculation with an intermediate temperature T 1 =1200°K, gave a value of D =2360 m/sec for a Chapman-Jouguet detonation.

Apparatus and method for measuring pressures and indicating leaks with optical analysis

Abstract: A partial pressure gauge utilizes an efficient electron collision excitation source yielding de-excitation radiation characteristic of residual gases. The intensity of a given spectral line is proportional to the partial pressure of the gas having such spectral line, and the current drawn from the excitation source provides a measure of the total pressure. A calibration technique based upon comparing the emitted light intensity with the ion currents associated with the excitation process yields an accurate measure of the relative partial pressure. Use of a filter to selectively pass radiation from a known constituent in known proportion in ambient gas provides an indication of the presence of a leak without the need for probing with a test gas. Provision for passing an evaporant stream through the excitation region permits accurate monitoring of the evaporant flux from which depostion rate is determined. In combination with techniques for achieving high differential sensitivity to iluctuations in light output from a selected spectral line, a novel leak detector is achieved. In combination with an optically dispersive element a residual gas analyzer is obtained.

Optimization of Two-Dimensional Scramjet Inlets

Abstract: The classical optimization of two-dimension al supersonic inlets for maximum total pressure recovery is extended to two-dimensional scramjet inlets. The result that optimal supersonic inlets have shock waves of equal strength is often applied to scramjets. However the typical flow turning constraint required for scramjets, along with the lack of a terminating normal shock, lead to a more involved optimization problem. Despite this, optimization by the method of Lagrange multipliers indicates that scramjet inlets with maximum total pressure recovery have external shocks with almost equal strength. The optimal total pressure recovery and turning angles for some typical scramjet inlet configurations with up to five shocks are presented.