Showing papers on "Dynamic pressure published in 1979"

Numerical solution of problems in incompressible fluid flow: treatment of the velocity-pressure coupling

Abstract: Coupling between the momentum and mass conservation equations for “ incompressible” flows is often the major cause of the slow convergence of iterative solution techniques. Several methods of handling this coupling, some of which are novel, are examined, and results of their application to a test problem are compared. The application is made in a manner that completely isolates the effect of the coupling and leads to a clearer understanding of how the methods perform. Several recommendations are made for potential users.

Perturbation Pressure and Cumulus Convection

Abstract: A simple model of perturbation pressure in cumulus convection is presented. The results show that the buoyancy- and drag-induced perturbation pressures act against the prescribed forcing. The dynamic pressure is found to be a consequence of the Bernoulli effect and a balance for the centrifugal force which arises from the curved motion of the air. Quantitative calculations reveal that the pressure force is of the same order of magnitude as the buoyancy and drag and offers a plausible explanation for the acceleration of negatively buoyant air near the base of convective updrafts.

A Non-Archimedean Approach to the Equations of Convection Dynamics

Abstract: A new formulation of the momentum equations in convection dynamics is presented, dividing the pressure into separate hydrostatic and dynamic components. In this formulation, termed non-Archimedean, convection is envisaged as developing through the horizontal gradient of a time-dependent hydrostatic pressure, rather than the customary buoyancy. It is shown that in the vertical momentum equation there is only one forcing term, viz., the vertical gradient of the dynamic pressure rather than the customary combination of perturbation-pressure gradient and buoyancy force. In the multi-dimensional case, the new formulation leaves the vorticity form of the momentum equation unchanged from that obtained in the customary approach. A diagnostic equation is presented for computing the dynamic pressure component.

Method and means for measuring flow of a two phase fluid

Abstract: A Pitot tube is provided for measuring fluid momentum in a transmission line. A signal is transmitted through the Pitot tube to the fluid, and return energy is detected to determine the gas or liquid phase of the fluid at the point of momentum measurement, thus providing a more accurate measurement of fluid flow. Two Pitot tubes may be employed to determine absolute pressure or momentum and static pressure, from which the dynamic pressure is determined. The transmitted signal may be ultrasonic, electrical, or optical.

Patterns of Dynamic Pressure Increment of Formation-Fluid Flow in Large Drainage Basins, Exemplified by the Red Earth Region, Alberta, Canada

Abstract: Analysis of approximately 600 stabilized formation-fluid pressures in northern Alberta indicates a correlation of pore pressures not only with depth of measurement but also with elevation of the well-head. Deviations of observed formation pressures from nominal hydrostatic values were plotted against depth and elevation and were found to be arranged according to patterns expected theoretically for gravity-induced and regionally unconfined flow systems of various boundary conditions. These pressure differences are therefore considered to represent the difference between static and dynamic conditions and are termed the dynamic pressure increment. Effects of geologic heterogeneities and the topographic relief on the subsurface pressure-distribution are reflected by changes in the vertical and lateral spacing of the iso-p contours as well as by their configuration. The method does not give site-specific information on pressure and flow conditions; rather it indicates the type, nature and dimensions of the flow systems. On the basis of comparisons between observed and theoretically generated patterns of p (d, z) three major hydrodynamic zones were recognized in the area of study. Both the general conclusions and, to some extent, the details of the analysis based on the dynamic pressure increment were corroborated by and complementary to analyses of formation-fluid dynamics by other energy-related parameters. Consequently, the dynamic pressure increment is considered to be a valid parameter in the study of formation-fluid flow in large drainage basins.

Settling Times of Pressure Measurements through Capillary Tubes

Abstract: A settling time of pressure instrumentation connected through long, thin capillary tubes is studied theoretically and experimentally. A nonlinear partial-differential equation of heat flow type is derived under an assumption of laminar subsonic isothermal flow for pressure variations along tubes with small radius to length ratios. The equation is integrated numerically for problems with initial stepwise pressure difference assumed to be at the open end of tubes (case A) or at the junction of tubes and pressure transducers (case B); the results are compared with experiments, which show fair agreement as long as the Reynolds number is small. The pressure settling times are shown to depend heavily on the tube radius to length ratio, the tube inside volume to pressure transducer cavity volume ratio, and the absolute value of the pressure to be measured, whereas the dependence on the initial pressure difference across the tube is weak. The existence of a front of pressure variation that travels within tubes is proved and the speed of compression fronts is shown to be smaller than that of expansion ones. The approximate settling time estimation formulas appropriate for very long, thin capillary tubes are presented.

Pressure and velocity measurements in a three-dimensional wall jet

Abstract: The effects on the flow fields of varying the ratio of the velocity at the exit plane of the nozzle to the outer tunnel flow are reported. The pressure-velocity correlations are taken and some trends are discussed. Emphasis is placed on comparing the coherence between the fluctuating pressure and velocity fields at various locations in the different flow configurations.

Pressure instrumentation for gas turbine engines - A review of measurement technology

Abstract: Many types and designs of pressure measuring instrumentation are used during the development and testing of gas turbine engines. This paper provides an overview of more commonly available pressure transducers and their characteristics. Probe designs for use in both steady-state and dynamic pressure measurement systems are reviewed. Techniques used to qualify instrument probes and the methods used to calibrate pressure transducers during engine testing are described.

Aircraft Wake Flow Effect and Horizontal Tail Buffet

Abstract: As part of a program to investigate the fluctuating pressure distribution and response behavior of a fighter aircraft in transonic maneuver, an F-5A scale model has previously been tested in an 11-ft transonic wind tunnel. The model, with a number of static and dynamic pressure transducers imbedded in the lifting surfaces was tested at various angles of attack up to 16 deg. In this paper, test results of particular interest to wake flow and horizontal tail buffet are described. It is shown that the dynamic pressure data on the tail surface at the specified flight conditions serve to determine the local dynamic loads. They also influence the control performance of the aircraft under maneuver conditions where buffet is encountered. The data presented demonstrate a number of contributing factors that affect the tail dynamic pressures in the transonic regime.

Static pressure gaseous matter bearing equipped with bearing surface in both radial and thrust directions

Abstract: PURPOSE:To improve load capacity by dint of dynamic pressure effect by making bearing gaps at the intermediate parts between plural rows of air feeding bores in the circular direction smaller than settled static pressure bearing gaps. CONSTITUTION:A cylindrical surface 120 of an annulus 105 has two rows of air feeding bores 109, 109 installed at the same intervals on the circle having the same sectional surface. An axle 101 and plural air feeding bores 110, 110' installed at the same intervals on the circle with the axial core constitutes thrust type of static pressure bearing surface which is situated in the middle of annular flat surfaces 111, 111' and has self-throttle. Annular flat surfaces 112, 112' installed on side plates 104, 103 constitutes thrust type of static pressure bearing part through settled bearing gaps 113, 113' between 110, 110'. Static pressure bearing gaps 118, 118' are provided between circular surfaces 121, 121' and the cylindrical surface 120, while between the air feeding bores 109, 109' is provided a bearing gap 119 which is smaller than the static pressure bearing gaps, to improve the load capacity by dint of the dynamic pressure effect.