Total pressure

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

Behavior of shock trains in a diverging duct

Abstract: A shock train inside a diverging duct is analyzed at different pressure levels and Mach numbers. Nonreactive pressurized cold gas is used as fluid. The structure and pressure recovery inside the shock train is analyzed by means of wall pressure measurements, Schlieren images and total pressure probes. During the course of the experiments, the total pressure of the flow, the back pressure level and the Mach number upstream of the compression region have been varied. It is shown that the Reynolds number has some small effect on the shock position and length of the shock train. However, more dominant is the effect of the confinement level and Mach number. The results are compared with analytical and empirical models from the literature. It was found that the empirical pseudo-shock model from Billig and the analytical mass averaging model from Matsuo are suitable to compute the pressure gradient along the shock train and total pressure loss, respectively.

Large Eddy Simulation of Transonic Flow Field in NASA Rotor 37

Abstract: The current paper reports on numerical investigations on the flow characteristics in a transonic axial compressor, NASA Rotor 37. The flow field was used previously as a CFD blind test case conducted by American Society of Mechanical Engineers in 1994. Since the CFD blind-test exercise, many numerical studies on the flow field in the NASA Rotor 37 have been reported. Although steady improvements have been reported in both numerical procedure and turbulence closure, it is believed that all the important aspects of the flow field have not been fully explained with numerical studies based on the Reynolds Averaged Navier-Stokes (RANS) solution. Experimental data show large dip in total pressure distribution near the hub at downstream of the rotor at 100% rotor speed. Most original numerical solutions from the blind test exercise did not predict this total pressure deficit correctly. This total pressure deficit at the rotor exit was attributed to a hub corner flow separation by the author. Several subsequent numerical studies with different turbulence closure model also calculated this dip in total pressure rise. Also, several studies attributed this total pressure deficit to a small leakage flow coming from the hub in the test article. As the experimental study cannot be repeated, either explanation cannot be validated. The primary purpose of the current investigation is to investigate the transonic flow field with both RANS and a Large Eddy Simulation (LES). The RANS approach gives similar results presented at the original blind test exercise. Although the RANS calculates higher overall total pressure rise, the total pressure deficit near the hub is calculated correctly. The numerical solution shows that the total pressure deficit is due to a hub corner flow separation. The calculated pressure rise from the LES agrees better with the measured total pressure rise especially near the casing area where the passage shock interacts with the tip clearance vortex and flow becomes unsteady due to this interaction. The LES simulation also calculates the total pressure rise deficit near the hub and it agrees well with the measured data.

High-Temperature Wetting of Sapphire by Aluminum

Abstract: Sessile drop studies of molten aluminum on single-crystal sapphire substrates were conducted to investigate the effects of atmosphere on contact angle, substrate reactions, and interfacial crystal growth. Unlike previous investigations performed briefly in a vacuum environment in a temperature range within 600°C of the aluminum melting point, these experiments were conducted at higher temperatures (1200° to 1600°C) and at 1-atm total pressure over longer experimental times to more closely approach equilibrium conditions. A continuously flowing buffered gas system utilizing high-purity metered mixtures of hydrogen and helium in combination with a thoria ceramic electrolyte sensor were employed to achieve variations of the oxygen partial pressure from 10−19 to 10−15 atm while continuously maintaining the total pressure at 1 atm. At constant temperature, it was found that neither the oxygen partial pressure nor the crystallographic orientation of the sapphire substrate had a significant effect on the observed contact angles. A continuous decrease of acute contact angles and a single reaction ring characterized the 8-h experiments without the alternating spreading and contracting behavior repeatedly reported in the literature. This phenomenon can be attributed to the lower rate of metal evaporation and interfacial reaction at the higher total gas pressure and yet extremely low oxygen partial pressure of these experiments. Profilometric analysis of sapphire substrates subsequent to the removal of the quenched sessile drops indicates a reduction in metal–solid interaction due to the closer approach to equilibrium than in previous studies. An epitaxial orientation with respect to the substrate was observed in α-alumina crystallite formation at the metal–ceramic interface. Experimental evidence suggests that it was formed by a nucleation and growth process during the cooling period.