Showing papers on "Dynamic pressure published in 1993"

Performance and test section flow characteristics of the National Full-Scale Aerodynamics Complex 80- by 120-Foot Wind Tunnel

Abstract: Results from the performance and test section flow calibration of the 80- by 120-Foot Wind Tunnel are presented Measurements indicating the 80- by 120-ft test section flow quality were obtained throughout the tunnel operational envelope and for atmospheric wind speeds up to approximately 20 knots Tunnel performance characteristics and a dynamic pressure system calibration were also documented during the process of mapping the test section flow field Experimental results indicate that the test section flow quality is relatively insensitive to dynamic pressure and the level of atmospheric winds experienced during the calibration The dynamic pressure variation in the test section is within +/-75 percent of the average The axial turbulence intensity is less than 05 percent up to the maximum test section speed of 100 knots, and the vertical and lateral flow angle variations are within +/-5 deg and +/-7 deg, respectively Atmospheric winds were found to affect the pressure distribution in the test section only at high ratios of wind speed to test section speed

Goddard problem in presence of a dynamic pressure limit

Abstract: The Goddard problem is that of maximizing the final altitude for a vertically ascending, rocket-powered vehicle under the influence of an inverse square gravitational field and atmospheric drag. The present paper deals with the effects of two additional constraints, namely, a dynamic pressure limit and specified final time. Nine different switching structures involving zero-thrust arcs, full-thrust arcs, singular-thrust arcs, and state-constrained arcs are obtained when the value of the dynamic pressure limit is varied between zero and infinity and the final time is specified between the minimum possible time within which all of the fuel can be burned and the natural final time that emerges for the problem with final time unspecified. For all points in the aforementioned domain of dynamic pressure limit and prescribed final time, the associated optimal switching structure is clearly identified. Finally, a simple intuitive feedback law is presented for the free time problem. For all values of prescribed dynamic pressure limit, this strategy yields a loss in final altitude of less than 3 percent with respect to the associated optimal solution.

Magnetospheric response to solar wind dynamic pressure variations: Interaction of interplanetary tangential discontinuities with the bow shock

Abstract: Some magnetic impulse events observed in the polar region are related to vortices associated with plasma convection in the ionosphere. Recent analyses of satellite and ground data suggest that the interaction of solar wind dynamic pressure pulses and the magnetosphere may lead to the formation of velocity vortices in the magnetopause boundary layer region. This can in turn lead to the presence of vortices in the polar ionosphere. However, before reaching the Earth's magnetopause, these interplanetary pressure pulses must interact with and pass through the bow shock. A variation of the solar wind dynamic pressure may be associated with shocks, magnetic holes, or tangential discontinuities (TDs) in the interplanetary medium. We study the interaction of interplanetary TDs with the Earth's bow shock (BS) using both theoretical analysis and MHD computer simulations. It is found that as a result of the collision between a TD and the BS, the jump in the solar wind dynamic pressure associated with the TD is significantly modified, the bow shock moves, and a new fast shock or fast rarefaction wave, which propagates in the downstream direction, is excited. Our theoretical analysis shows that the change in the plasma density across the interplanetary TD plays the most important role in the collision process. In the case with an enhanced dynamic pressure behind the interplanetary TD, the bow shock is intensified in strength and moves in the earthward direction. The dynamic pressure jump associated with the transmitted TD is generally reduced from the value before the interaction. A fast compressional shock is excited ahead of the transmitted TD and propagates toward the Earth's magnetosphere. For the case in which the dynamic pressure is reduced behind the interplanetary TD, the pressure jump across the transmitted TD is substantially weakened, the bow shock moves in the sunward direction, and a rarefaction wave which propagates downstream is excited. We also simulate and discuss the interaction of a pair of tangential discontinuities, which may correspond to a magnetic hole, with the BS.

An improved method to determine free stream conditions in hypersonic facilities

Abstract: For determing pressure coefficients and Stanton numbers from the measured surface pressures and heat fluxes at a model surface, the dynamic pressure, mass flux and the total enthalpy of the free stream have to be known. Usually these values are determined by computing the wind tunnel nozzle flow. But a lot of uncertainties enter the computation which may lead to unreliable results. Therefore, a simple method was developed which yields the desired free stream conditions with high accuracy. This could be achieved by using mainly values which are measured within the test section. The method requires the measurement of the Pilot pressure, the stagnation point heat flux on a sphere and the static pressure of the free stream. For the static pressure an estimated value can also be used, because it has no large influence on the result. Some simple considerations show that the derived method is also valid for nonequilibrium free stream conditions. With the procedure presented the accuracy of the pressure coefficients and Stanton numbers could be increased significantly. Further, it improved the repeatability of these test results. This is very important for fundamental research, for the design of hypersonic vehicles as well as for CFD-validation with experimental data. The application of the method presented is not limited to short duration facilities, it can also be used for continuously working wind tunnels.

NASA Lewis 8- by 6-foot supersonic wind tunnel user manual

Abstract: The 8- by 6-Foot Supersonic Wind Tunnel (SWT) at Lewis Research Center is available for use by qualified researchers. This manual contains tunnel performance maps which show the range of total temperature, total pressure, static pressure, dynamic pressure, altitude, Reynolds number, and mass flow as a function of test section Mach number. These maps are applicable for both the aerodynamic and propulsion cycle. The 8- by 6-Foot Supersonic Wind Tunnel is an atmospheric facility with a test section Mach number range from 0.36 to 2.0. General support systems (air systems, hydraulic system, hydrogen system, infrared system, laser system, laser sheet system, and schlieren system are also described as are instrumentation and data processing and acquisition systems. Pretest meeting formats are outlined. Tunnel user responsibility and personal safety requirements are also stated.

Advanced launch system trajectory optimization using suboptimal control

Abstract: The maximum-final mass trajectory of a proposed configuration of the Advanced Launch System is presented. A model for the two-stage rocket is given; the optimal control problem is formulated as a parameter optimization problem; and the optimal trajectory is computed using a nonlinear programming code called VF02AD. Numerical results are presented for the controls (angle of attack and velocity roll angle) and the states. After the initial rotation, the angle of attack goes to a positive value to keep the trajectory as high as possible, returns to near zero to pass through the transonic regime and satisfy the dynamic pressure constraint, returns to a positive value to keep the trajectory high and to take advantage of minimum drag at positive angle of attack due to aerodynamic shading of the booster, and then rolls off to negative values to satisfy the constraints. Because the engines cannot be throttled, the maximum dynamic pressure occurs at a single point; there is no maximum dynamic pressure subarc. To test approximations for obtaining analytical solutions for guidance, two additional optimal trajectories are computed: one using untrimmed aerodynamics and one using no atmospheric effects except for the dynamic pressure constraint. It is concluded that untrimmed aerodynamics has a negligible effect on the optimal trajectory and that approximate optimal controls should be able to be obtained by treating atmospheric effects as perturbations.

Dynamic Pressure of Water and Sediment on Rigid Dam

Abstract: Earthquake response of reservoir sediment and its dynamic interaction with the impounded water are analyzed using a two‐dimensional model of poroelastic media. The pressure wave equation for the pore water and the sediment is solved by an implicit finite difference method coupled with a fast Poisson solver. The numerical scheme requires a conversion of the boundary condition on the rigid dam face to a Dirichlet boundary condition. For incompressible impounded water, a reduction in the dynamic pressure appears at the onset of ground motion when the bulk modulus of pore water in the sediment is compressible. The pressure rises rapidly with the celerity of pressure wave and exceeds that of Westergaard's solution for the incompressible case without the sediment. Augmentation of the pore pressure is primarily caused by the inertia of the sediment and the Stokes drag. The hydrodynamic pressures on the dam face could exceed significantly those calculated by an incompressible two‐fluid model for an idealized liqu...

Theory of the Equation of State at High Pressure

Abstract: of quantum and statistical mechanics. The application of pressure offers a means by which the lattice constant or density may be varied, thus resulting in changes in properties, including transitions to new structures or phases and modif ications in electronic configurations. This review focuses on how the application of theor etical techniques has provided a deeper under­ standing of these changes on an atomistic level. Recent theoretical developments have resulted from rapid advances in computational capabilit ies and high-pr essure experi mental techniques. Accurate measurements are now carried out by static and dynamic methods to pressures of several Mbar and several thousand Kelvins, and these have stimulated new theoretical efforts.

CVT contact-pressing device with electronic control, in particular for highly dynamic operating conditions

Abstract: Contact-pressing device for CVT (continuously variable transmission), comprising both pressure medium supply devices and open-loop and closed-loop control devices for the contact pressure, for operating conditions having spontaneous torque loading peaks. Ensuring and building up sufficient contact pressure force in the case of highly dynamic operation require relatively large pressure medium supply devices, because of the elasticities necessarily present in the hydraulic and mechanical systems and components of the CVT (inertias). Obvious, correspondingly largely dimensioned contact pressure and adjusting pressure medium supply devices on the CVT, which could undertake this task concomitantly but would have to operate continuously under the highest disk set pressure, are not acceptable on economic grounds. Solutions according to the invention of low-loss, highly dynamic pressure medium supply, open-loop and closed-loop control systems exist in the following embodiment versions as a result of the arrangement of: - a pressure store and a rapidly switching digital-process computer-controlled servo valve which modulates contact pressure peaks to the basic contact pressure set for static operating conditions; - a modification having a differential piston which increases the contact pressure with respect to the store pressure level; - an additional or separate, largely dimensioned hydraulic pump which, in normal operation, delivers in a low-pressure and low-loss manner in a circuit and is only activated as required for the spontaneous increase of contact pressure force. A further useful effect consists... Original abstract incomplete.

Brake system for vehicle

Abstract: PURPOSE: To suppress the change in the brake operation feeling in the electronic control for the brake power or in the failure of the electronic control and secure the brake power in the failure of the electronic control, at the same time as for an electronic control type brake system. CONSTITUTION: A front wheel brake 8 for a front wheel FW is connected with the static pressure brake systems A1 and A2 for introducing the liquid pressure from a tandem master cylinder 1, and a wheel brake 9 for a rear wheel RW is connected with the dynamic pressure brake systems B1 and B2. The hydraulic pressure generated by a high liquid pressure generator 5 is pressure-adjusted by an electronically controlled pressure control valve 6 and sent into the dynamic pressure brake system. An electronic controller 7 receives the outputs of a brake operation detector 3 and a vehicle deceleration speed sensor 4, and outputs a drive signal to the pressure control valve 6 so that the output of the sensor 4 develops a prescribed relation for the output of the detector 3. COPYRIGHT: (C)1995,JPO

Apparatus for dynamic wind pressure test for body to be tested

Abstract: PURPOSE:To enable reproduction of virtual conditions of typhoon by generating a differential pressure from an internal pressure of a pressure chamber and by supplying a wind at the same time onto the surface of a body to be tested such as a curtain wall or a glass panel from free directions, regarding an apparatus for a dynamic wind pressure test which conducts tests on wind pressure resistance, airtightness and water tightness and others by generating a dynamic pressure as well as a static pressure for the body to be tested such as the curtain wall. CONSTITUTION:A pressure chamber 1 one side of which is made an opening 4 for fitting hermetically a body W to be tested, and a static-pressure loading device 2 which has a blast port 10 provided on the side facing the body fitted to the pressure chamber and the pressure of which is adjustable, are provided. Moreover, a dynamic- pressure loading device 3 in which a trunk air port 11 and a suction port 12 are formed oppositely on the lateral sides of the pressure chamber and in the vicinity of the surface of the body fitted to the chamber and are connected with each other by an airtight duct 20 outside the pressure chamber, while an axial flow blower 21 is provided in an appropriate place of the airtight duct, is provided.

Flow visualization by velocity-pressure cross-correlation

Abstract: For a better understanding of turbulent structure, a new flow visualization method of the time averaged structure of the turbulence has been developed by using wall pressure fluctuations to detect the velocity fluctuations of the flow. Velocity fluctuations were visualized by the measured velocity-wall pressure cross-correlation with the whole flow field for various time-delays between two measured values. Turbulence structures of a backward-facing step flow were investigated for three different flow regions--the recirculating flow just behind the step, the reattachment flow, and the boundary layer flow far down stream from the step. Sequential contour maps of cross-correlation values were calculated to display movement and deformation of turbulent structures both qualitatively and quantitatively.

Experimental evaluation of crack propagation velocity in pmma under dynamic pressure loading

Abstract: The pressure chamber is an open vessel, whose top end is sealed with a MELINEX** membrane, avoiding any membrane distortion. It is, then, pressurized up to a certain level, lower than the 2 bar. After the required presure has been reached (burst pressure), the knife at the bottom part is released, breaking the membrane at its center and along two perpendicular diameters. A pressure wave, which is directed along the expansion chamber against the specimen, is generated. It expands in the atmosphere through a gap between the bottom face of the specimen and the top flange of the expansion chamber. The blast wave is reproducible and its front is a plane.

The Interpretation of Internal Pressure Patterns of Rotating Stall in Centrifugal Compressor Impellers

Abstract: Dynamic pressure measurement on the shroud wall for a high performance single stage centrifugal compressor has been implemented to record the unsteady pressure data during rotating stall. Apart from the frequency analysis of the stall characteristics, a computer-aided method has been developed to enable the unsteady internal pressure patterns inside the blade channel near shroud surface to be described and shown in an animated visualisation.Typical results of internal pressure patterns for a backswept impeller with two cell rotating stall occurrence at the impeller speed of 16000 rpm are presented in detail. The internal flow structure can be interpreted by pressure patterns of three types emerged consecutively within one time period of stall pressure oscillation: the normal pattern, the mixed pattern and the stalled pattern. The mixed pattern is characterized by a coexistence of the reverse movement of high pressure region towards inlet and the inlet separation. The stalled pattern is characterized by a collapse of pressure loadings in the blade channel. Such observation is thought to be useful for exploring the flow mechanism of rotating stall.© 1993 ASME

System and method for measuring the speed of fluid flow of varying direction

Abstract: An object of spherical shape is disposed in such a way that it changes thepeed of any flow of two-dimensionally varying direction to the same extent. The dynamic pressure on the object, relative to the ambient, is so measured that there exists a unique and theoretically determined relation between the pressure and the speed of approaching flow.

Dynamic pressure bearing made of ceramics and grooving method

Abstract: PURPOSE:To provide a ceramic dynamic pressure bearing and grooving method for it by which the quantity of fine particulates generated in the machining face of a fluid dynamic pressure generating groove can be reduced or eliminated and the machining of the ceramic material after the formation of the fluid dynamic pressure generating groove can be eliminated. CONSTITUTION:A dynamic pressure generating groove 2 is formed by radiating YAG pulse laser beams on the sliding face 1a of a bearing base body 1 made of ceramics of Sic, Si3N4, and Al2O3. On the internal surface of this dynamic pressure generating groove 2, a refined layer 2a comprising ceramics, which is the base metal of the ceramic bearing base substrate 1, melted and solidified is formed.

Pitot-tube type probe

Abstract: PURPOSE:To measure a speed accurately even in a low-speed region, wherein the changing rate of dynamic pressure is small, and to obtain aerodynamic data for the speed and the flying attitude accurately even under the conditions of cross wind and downwash CONSTITUTION:A total-pressure pipe is arranged at the apex part of a multiple- pyramid trapezoid A pressure hole is arranged in each pyramid surface A Pitot tube 1 determines the velocity vector of flow and the static pressure based on the pressure received with the total pressure pipe and the pressure received with the pressure hole A screening duct 10 is provided at the outer surface part of the pitot tube 1 so that a wind path 11 is formed and the tip of the duct is made to extrude slightly from the tip part of the Pitot tube A suction-flow generating means for generating the suction flow in the axial direction is provided at a part close to the rear part of the screening duct 10 The wind flow is artificially generated in the duct at a low-speed region Thus, the dynamic pressure is shifted, and the change is made large

Brake pressure control for hydraulic vehicle braking system - has throttle element to create dynamic pressure in return flow pipe

Abstract: Brake pressure control arrangement for a hydraulic vehicle braking system in which the inlet valve (6) has a control piston (32,34) which is subjected to pressure in a return flow pipe (12) against a compression spring (37). The return flow pipe contains a controllable outlet valve (11) which blocks the pipe in its rest position and frees the pipe in its switching position, and downstream of the outlet valve a throttle element (13) is provided to create a dynamic pressure in the return flow pipe when the outlet valve is open. ADVANTAGE - Low cost brake pressure control which gives a rapid pressure drop on opening the outlet valve.

Pressure-related driving forces in the fully filled nonintermeshing twin screw extruder

Abstract: Research in understanding the mechanisms behind driving forces in the fully filled nonintermeshing twin screw extruder concentrated on experimental analysis of the relation between stagger, screw speed, and cross-channel flow due to measured pressure differential in the nip region. A new measure of the pressure driving force was also sought out, to correlate new data to previous findings from visual studies. The first part of the study was to obtain the values for the dynamic pressure on both sides of the nip region. Further refinements to the equipment used in previous studies allowed closer placement of the transducers in the nip region. After the data were stored, analysis started by determining the δp values from the trace of the pressure differential. By plotting these values, we obtain a highly repeatable curve confirming that the greatest pressure flow occurs at small staggers. A simple 2-D model for pressure flow in the nip region was used to estimate the effect of the cross-channel pressure differential. Values for the cross-channel pressure flow were calculated and compared with the drag flow and found to be significant. © 1993 by John Wiley & Sons, Inc.

Gas turbine power plant - has separating walls for separate guidance of hot gas flows through low pressure turbine

Abstract: The plant has a dynamic pressure engine (13), and a turbine (14) with a high pressure (22) and low pressure turbine (23). There is a high pressure motor gas pipe (21) between engine and high pressure turbine, and a low pressure pipe (24) between engine and low pressure turbine. This forms a low pressure stage of the high pressure turbine, and is connected to it. Elements (28-31) are provided, to pass the hot gas flows from the low pressure motor gas pipe and the high pressure turbine separately through the low pressure turbine. The elements consist of separating walls (28,29) in the low pressure turbine. They prevent mixing of the two hot gas flows. Further separating walls (30) are located in front of the low pressure turbine. USE/ADVANTAGE - Improved low pressure turbine efficiency in gas turbine power plant.

Pressure-proof water-proof sealing system using unidirectional dynamic pressure bearing

Abstract: PURPOSE: To lengthen a life span by forming a dynamic pressure generating groove to prevent inflow of a pressure fluid to the side of a dynamic pressure bearing between the dynamic pressure bearing and the pressure fluid, to blow a fluid between both of cylindrical sliding members on the rotary side and the fixed side and to flow the fluid to the side of the pressure fluid through an oil sealing means. CONSTITUTION: When a pump shaft 9 is rotated, as a rotary side cylindrical ceramic sliding member 92a is rotated, a function to pump a fluid 94 in a fluid reserve room 93 to the side of a pressure fluid is generated by a unidirectional dynamic pressure bearing 92. The fluid 94 in the fluid reserve room 93 passes a radial gap between the rotary side dynamic pressure bearing constitutional element 92a and a fixed side cylindrical ceramic sliding member 92b and is flowed unidirectionally to the side of the pressure fluid through an oil sealing means 33. Consequently, as the oil sealing means 33 and the unidirectional dynamic pressure bearing 92 constitute a means to pass the fluid 94 unidirectionally, it is possible to constitute a perfect pressure proofed and water proofed sealing system. Even in the case of high speed rotation, the rotation axis and the bearing make contact with each other in line, it is possible to lengthen a life span and to lower noise and oscillation. COPYRIGHT: (C)1994,JPO

X-31a flight flutter test excitation by control surfaces

Abstract: which interfaced with the aircraft digital, flyby-wire control system. This paper describes the characteristics and use of the flutter excitation system, including the control box, the control surfaces operated, a block diagram of the interfaces with the control system, the sine sweep, dwell and pulse capabilities of the system, the oscillation frequency vs time, and typical amplitudes and phase angles of control surface rotation versus time. The flight envelope cleared, the real -time telemetry parameters monitored, and the test procedures used are briefly described. Typical time histories of response, and typical plots of the frequencies and damping versus dynamic pressure and mach number extracted from the response data are given. The required structural modes were adequately excited by the control surface sine sweeps used. Extrapolation of the plots of frequencies and damping versus dynamic pressure and mach number indicated large flutter margins of safety for the X-31A, which is in agreement with flutter analyses conducted prior to flight flutter tests.

Transition Aerodynamics for 20-Percent-Scale VTOL Unmanned Aerial Vehicle

Abstract: An investigation was conducted in the Langley 14- by 22-Foot Subsonic Tunnel to establish a transition data base for an unmanned aerial vehicle utilizing a powered-lift ejector system and to evaluate alterations to the ejector system for improved vehicle performance. The model used in this investigation was a 20-percent-scale, blended-body, arrow-wing configuration with integrated twin rectangular ejectors. The test was conducted from hover through transition conditions with variations in angle of attack, angle of sideslip, free-stream dynamic pressure, nozzle pressure ratio, and model ground height. Force and moment data along with extensive surface pressure data were obtained. A laser velocimeter technique for measuring inlet flow velocities was demonstrated at a single flow condition, and also a low order panel method was successfully used to numerically simulate the ejector inlet flow.

Optimal Flight Paths with Constrained Dynamic Pressure

Abstract: This paper presents optimal aircraft motion subject to constrained dynamic pressure. The aircraft is modeled as a point mass in the three-dimensional space. Two optimal control problems are solved: 1) range maximization in fixed time, 2) minimum time intercept of a moving target. At first all combinations of active state and control constraints are considered to determine the possible types of optimal control. They are composed to give the optimal switching structures of 1) and 2). Extremals for various boundary conditions are obtained with multiple shooting. Along the dynamic pressure boundary a) full throttle, b) partial throttle and c) minimum thrust subarcs occur, b) is a singular control, c) is a chattering control.