Showing papers on "Dynamic pressure published in 1986"

An Improved Control Volume Finite-Element Method for Heat and Mass Transfer, and for Fluid Flow Using Equal-Order Velocity-Pressure Interpolation

Abstract: A new control volume-based finite-element method for the solution of heat, mass, and momentum transfer equations is presented. As compared with other similar methods, the new feature of the proposed method lies in the choice of the particular shape function that accounts explicitly for the source terms in the transport equations. The use of such a shape function for interpolating the velocity components while discretizing the continuity equation leads, very naturally, to a consistent equal-order formulation that permits velocity and pressure to be computed at all the grid points in the domain. The method is applied to a number of test problems, and in all cases the results are found to be more accurate than those obtained by its predecessors.

Air pressure measurement element and system incorporating same

Abstract: A unitary element for use in measuring the total and static pressure of a gas flowing through a duct is disclosed in a preferred embodiment. The element is elongated and hollow, having a continuous, impermeable wall dividing the interior into total and static pressure chambers. In cross section, the element is of aerodynamic or airfoil shape, having a curved forward edge and converging toward the trailing edge adjacent which the outer surfaces are parallel for a short distance. Spaced openings along the forward edge and the upper and lower portions of the rearwardly converging wall portions communicate with the total and static pressure chambers, respectively. Separate manifolds communicate with the total and static pressure chambers of a plurality of such members arranged across an air flow duct to obtain average pressure readings across the cross section of the duct. Configuration of the measuring element and the position of the static pressure openings highly influence accuracy of the signals and permit velocity pressure readings which are amplified, yet linear over a wide range, with respect to actual velocity pressure within the duct.

Control law synthesis for an airplane with relaxed static stability

Abstract: The synthesis of a command and stability augmentation control law for a transport airplane is presented. To improve fuel efficiency, the airplane has a relatively small horizontal tail surface and therfore has unsatisfactory inherent longitudinal stability. Over a wide range of center-of-gra vity locations and the full flight envelope, the control law furnishes 1) task tailored column force gradients; 2) excellent dynamic responses for normal acceleration, pitch rate, and speed; and 3) better than f =0.5 damping for the phugoid and short period modes. The control law is based on linear quadratic Gaussian synthesis at a single operating point. The gains are scheduled as functions of dynamic pressure and airplane flap position. The control is the elevator command and the sensors are column force, normal acceleration, pitch rate, airspeed, longitudinal acceleration, and vertical speed.

Nearly-grazing optimal trajectories for aeroassisted orbital transfer

Abstract: In the present treatment of optimal control problems arising in the study of coplanar aeroassisted orbital transfer, the hybrid combination of propulsive parameters in space and aerodynamic maneuvers employing lift modulation in the sensible atmosphere indicates that the optimal energy-viewpoint solution is the grazing trajectory; this trajectory is characterized by favorable values of the peak heating rate and the peak dynamic pressure. Numerical solutions are obtained by means of the sequential gradient restoration algorithm for optimal control problems. It is found that nearly-grazing trajectories yielding the least-square value of the path inclination have desirable characteristics from the standpoints of energy, heating rate, and dynamic pressure.

Dynamic behaviour of paired metal hydrides II: Analytical survey of the experimental results

Abstract: The operational characteristics of a paired metal hydride system are strongly dependent on the amount of hydrogen gas which is transferred from one metal hydride as hydrogen donor to the other metal hydride as hydrogen acceptor. In such a dehydriding-hydriding process the amount of hydrogen gas which is transferable between the paired metal hydrides is considered as the result of the dynamic pressure-temperature-composition (P-T-C) behaviours in such a combined system. These dynamic P-T-C behaviours are studied from the experimental P-C and P-T diagrams in order to analyse the effect of operational parameters which influence the system characteristics. Correlations between dynamic P-C behaviours and static P-C relationships revealed that the actual pressure difference (defined as the dynamic pressure driving force) determines the pressure levels of the given system and the amount of hydrogen transferred through dehydriding and hydriding reactions. Three different types of pressure driving forces under equilibrium (static) conditions are also discussed in connection with the dynamic pressure driving force which is obtained from the experimental dynamic study of a paired metal hydride system.

Unsteady Pressure Measurements on a Biconvex Airfoil in a Transonic Oscillating Cascade

Abstract: Flush-mounted dynamic pressure transducers were installed on the center airfoil of a transonic oscillating cascade to measure the unsteady aerodynamic response as nine airfols were simultaneously driven to provide 1.2 deg of pitching motion about the midchord. Initial tests were performed at an incidence and angle of 0 deg and A Mach number of 0.65 in order to obtain results in a shock-free compressible flowfield. Subsequent tests were performed at an incidence angle of 7 deg and Mach number of 0.8 in order to observe the surface pressures with an oscillating shock near the leading edge of the airfoil. Results are presented for interblade phase angles of 90 and -90 deg and at blade oscillatory frequencies of 200 and 500 Hz (semi-chord reduced frequencies up to about 0.5 at a Mach number of 0.8). Results from the zero-incidence cascade are compared with a clasical usnteady flat-plate analysis. Flow visualization results depicting the shock motion on the airfoils in the high-incidence cascade are discussed. The airfoil pressure data are tabulated.

Excitation of Blade Vibration by Flow Instability in Centrifugal Compressors

Abstract: Experiments were conducted to investigate the interactions between blade vibrations and self-excited flow oscillations in a high performance centrifugal compressor system Unsteady pressure fluctuations and dynamic stress levels were measured during compressor operation near choke, in self-excited oscillating flow conditions and near surge for four different speed lines The unsteady pressure field for every operating condition was determined from the simultaneous recording of the output of twelve dynamic pressure transducers which were successively positioned in two peripheral and one meridional planes Corresponding blade vibration data were collected using an eight channel telemetry system transmitting the outputs of semi-conductor strain gages located on different blades Analysis of the measurements showed that the unsteady pressure field due to self-excited flow oscillations can be characterized by multiples of rotating and non-rotating pressure patterns at different frequencies The blade vibration signals clearly demonstrated the excitation of the blade by each of the different unsteady pressure patterns and the frequencies of the unsteady flow field demonstrates the complexity of this flow phenomena and the need to understand the mechanism of its occurrence in order to avoid blade resonance excitation and failure during compressor operationCopyright © 1986 by ASME

Three-dimensional computation of mixing of transverse injector in a ducted supersonic airstream

Abstract: Numerical solutions of the three-dimensional mass-averaged elliptic Navier-Stokes equations, including species transport, are obtained for nonreacting, turbulent, mixing flow fields for the case of transverse sonic injection of a secondary gas into a supersonic airstream through a circular orifice injector. Results are presented for flow through a constant area duct and through a duct with a rearward-facing step upstream of the injector. The equations are numerically integrated using MacCormack's explicit method and turbulence is included using the Baldwin-Lomax algebraic eddy viscosity model. In the species transport and energy equations, diffusion coefficients based on Fick's law and an assumption of unit Lewis number are applied. The computations were performed on a CDC-VPS-32 (extended version of Cyber-205) using a grid consisting of approximately 200,000 points. The computed results are compared with experimentally observed penetration and spreading boundaries for an injected gas at two dynamic pressure ratios. Three-dimensional flow field structures are dipicted in terms of static pressure, mass fractions of species and velocity vectors.

Oscillation pressure device for dynamic calibration of pressure transducers

Abstract: Method and apparatus for obtaining dynamic calibrations of pressure transducers. A calibration head (15), a flexible tubing (23) and a bellows (20) enclose a volume of air at atmospheric pressure with a transducer (11) to be calibrated subject to the pressure inside the volume. All of the other apparatus in the drawing apply oscillations to bellows (20) causing the volume to change thereby applying oscillating pressures to transducer (11) whereby transducer (11) can be calibrated.

Arrangement for influencing the flow on guide or rotor blades for turbo engines

Abstract: Arrangement for preventing the laminar flow separation of boundary layers on turbo engine blades by blowing out and sucking in flow fluid on the blade suction side by means of apertures at the pressure minimum and in the area of the flow separation, which are connected together, characterised in that their position is so selected that at Reynolds numbers of more than 200,000 equal pressure prevails at the apertures, whilst at Reynolds numbers of less than 100,000 a pressure differential of 5 to 10% of the outlet dynamic pressure is produced, thereby causing flow fluid to be blown in in the area of the flow separation.

Air flow rate measuring apparatus

Abstract: PURPOSE:To miniaturize the measuring apparatus with less height of a air collection hood, by arranging a static pressure detector within the air collection hood in two directions viewed from the center therein to detect an average static pressure. CONSTITUTION:An opening 1a of a air collection hood 1 is put on a diffusion port 11 in the ceiling. A pitot tube 2 for detecting static pressure is provided in cross within the air collection hood 1 to detect average static pressure in the hood. The hood 1 is also provided with a connection tube 4 to detect average total pressure with a pitot tube 5 therein. A fan is provided at the lower end of the connection tube 4 and adjusts a variable blower 8 so that the static pressure in the hood 1 may equal that in the room. Then, the average static pressure is subtracted from the average total pressure to calculate the average dynamic pressure from which air volume is determined. Thus, as the static pressure detector is arranged to detect the average static pressure in the air collection hood, the miniaturization of the air collection hood is possible thereby enabling highly accurate measurement with a smaller air flow rate measuring device.

Computer simulation of a wind tunnel test section with discrete finite-length wall slots

Abstract: A computer simulation of a slotted wind tunnel test section which includes a discrete, finite-length wall slot representation with plenum chamber constraints and accounts for the nonlinear effects of the dynamic pressure of the slot outflow jet and of the low energy of slot inflow air was developed. The simulation features were selected to be those appropriate for the intended subsequent use of the simulation in a wall interference assessment procedure using sparsely located wall pressure measurements. It is demonstrated that accounting for slot discreteness is important in interpreting wall pressure measured between slots, and that accounting for nonlinear slot flow effects produces significant changes in tunnel-induced velocity distributions and, in particular, produces a longitudinal component of tunnel-induced velocity due to model lift. A characteristic mode of tunnel flow interaction with constraints imposed by the plenum chamber and diffuser entrance is apparent in simulation results and is derived analytically through a simplified analysis.

Hydraulic brake-power booster unit

Abstract: A hydraulic brake-power booster unit is provided for a vehicle having a dual-circuit brake system and an antilock system operating according to the drain principle. When the brake system is intact, the booster unit provides dynamic pressure to one of the two brake circuits and static pressure admission to the other. The pressure to the static brake circuit takes place by the separate-power-assisted shifting of an emergency piston. On one side, the emergency piston delimits an output pressure space to which the brake circuit that can be statically acted upon by pressure is connected. This brake circuit also remains operable in the case of a breakdown of the hydraulic power source only by the operation of the pedal and the resulting possible shifting of the emergency piston. A path transducer generates an electrical signal proportional to the position of the emergency piston. A pressure transducer generates an electrical signal proportional to the pressure in the output pressure space for the static brake circuit. Starting from a minimum position of the emergency piston, the brake circuit that initially could be acted upon statically by pressure is now acted upon dynamically. The reversing is caused by a mechanically path-controlled reversing valve. When the actual value of the output pressure of the brake-power booster unit is lower than a desired value, an electronic comparison arrangement generates a warning signal.

Fluid pressure spool valve and method of controlling pressure forces acting thereon

Abstract: The velocity head created at an inlet port of a spool valve decreases the static pressure head at the inlet. The valve is so constructed that the decrease in static pressure can act on only a very small effective area of the land side surface, with a substantial majority of the land side surface effective area being so positioned that it is not subject to the velocity pressure head and its lesser static pressure head. Therefore the majority of the effective land side wall area is not exposed to the decrease static pressure head, but is exposed primarily to the full static pressure head with virtually no velocity pressure head, as the opposite land. This therefore decreases the force differential tending to urge the spool valve toward the closed position and therefore decreases the amount of force which must be overcome to move the spool valve in an opening direction. As a near balance of static pressures acting in opposite directions on the spool valve lands is obtained, there is less resistance to the valve apply force. This is accomplished by providing recessed land facing surfacing areas in one or both of the lands of a typical two-land spool valve.

Dynamic pressure calibrator

Abstract: A high pressure, short rise time pulse is generated by first pressurizing aarge chamber utilizing a pressure fluid. An initially closed channel communicates the large chamber with a small test chamber that is closed except for the channel and to which one or more pressure gauges are connected. One of the pressure gauges may be utilized as a standard to indicate pressure in the chamber while another one of the gauges can be calibrated utilizing the device. The channel is abruptly opened to discharge the high pressure fluid from the large chamber to the small test chamber. Only a small amount of fluid enters the small test chamber but the pressures in the large and small chamber are equalized rapidly so that the small chamber experiences a high pressure, short rise time pulse.

Bearing for optical deflector

Abstract: PURPOSE:To improve the performance of an optical deflector by engraving and providing a groove for generating a dynamic pressure, on the outside periphery of a fixed shaft of a static pressure fluid bearing, utilizing a static pressure when starting a rotation of the optical deflector, and switching it to a dynamic pressure driving, after it has reached a prescribed revolving speed. CONSTITUTION:On the upper face of a lower frame 4, a spiral groove 52 is engraved and provided so as to surround a revolving shaft 8, and on a part of this groove, a discharge port of a thrust fluid passage 18. Accordingly, a fluid which is discharged from the thrust fluid passage 18 through a radial fluid passage 15 from a hollow thrust hole 10 floats and rotates a thrust receiving member 30. When operating an optical deflector, first of all, it is started by utilizing a static pressure fluid bearing, and when the optical deflector has reached a prescribed rotating speed, it is operated as a dynamic pressure fluid bearing by operating a fluid on a herringbone groove which has been provided on the outside periphery of the revolving shaft. In this way, this optical deflector can be driven freely at a low speed and a high speed, and its performance is improved.

An instrument for measuring turbulent pressure fluctuations

Abstract: An instrument is described for laboratory measurements of the fluctuating static pressure in the turbulent boundary layer above progressive water waves It consists of a disk‐shaped sensing head properly designed to minimize the dynamic pressure variation to an acceptable level, a commercially available piezocrystal transducer housed inside a casing, and a forward‐bent connecting tube Pressure fluctuations sampled by the disk are converted into an electrical signal by the piezocrystal transducer Through low‐pass filtering, only the frequency range of interest is retained The instrument was tested successfully for frequency response, dynamic and mechanical noise sensitivity, and response to spurious pressure fluctuations (produced when operating in a Eulerian wave‐following mode) inside a cylindrical chamber and in a wind–wave facility, and some sample results along with the calibration procedures and data analysis are presented

Air speed indicator

Abstract: PURPOSE:To indicate the air wind speed at the time of low air wind speed by selecting air speed values converted from number of rotations of an air blower when the number of rotations of the blower is low rotational frequencies and selecting measured values of air speed measured by an air speedometer when the number of rotation is larger than it. CONSTITUTION:Total pressure and static pressure are detected by an air speedometer when a blower driving electric motor 12 is driven to rotate blades of an air blower 11 and wind of necessary air speed is generated in a measuring section 13. The detection signal is led to a differential pressure converter 15, and differential pressure (dynamic pressure) is converted to electric signals and inputted to a switching circuit 20 through a signal conditioner 16 and an A/D converter 17. On the other hand, the number of rotations of blades of the air blower 11 is detected by a pulse generator 18 attached to the electric motor 12 as a pulse train, and converted to an air speed value by an arithmetic circuit 19 through a counter and inputted to the circuit 20. The circuit 20 makes conversion of physical quantity based on each input signal and selects air speed values converted from the number of rotations of the blower, and when in excess of it, selects measured values of wind speed measured by the air speedometer, and sends to an indicator 21.

Guiding device with complex guide faces

Abstract: PURPOSE:To generate a large supporting force by providing a land section having a gap between the guiding face and the guided face smaller than other portions at one portion of a static pressure generating unit and forming many recesses having slant faces on the surface of the land section. CONSTITUTION:The return flow of the pressure fluid fed to a static pressure generating unit is controlled by a static pressure squeezing land section A2. The static pressure is generated in the static pressure generating band width L, and this static pressure is applied to the guiding face 21 of a rail member 2 and the guided face 31 of a moving member 3 to keep them at a fixed distance. In this case, a land section B1 holds a fixed small gap E not to bring the guided face 31 and the guiding face 21 into contact by the action of the static pressure. Accordingly, when the moving member 3 is moved in the straight line direction against the rail member 2, a fluid between many recesses 6 having slant faces 60 and opposing faces to them is compressed, and the dynamic pressure is generated.

Rotary hydraulic machine

Abstract: PURPOSE:To prevent a rotor from being vibrated by providing a passage which induces fluid having static pressure boosted inside a diffuser into a spacing defined between an impeller and a casing surrounding it in such direction that the circumferential flow speed of fluid in the diffuser is reduced. CONSTITUTION:Gas which is discharged from the outlet 35 of an impeller 3 flows into a fiffuser 5, in which dynamic pressure is converted to static pressure. A part of gas having static pressure boosted in the diffuser 5 passes through fluid passages 12 and 14 which open to casing faces 25 and 26 and then flows into spacing 8 and 10 defined between the impeller 3 and the casing 2 which surrounds the impeller 3 in the centripetal direction as shown by the arrow directions 13 and 15. Since fluid inside the spacing 8 and 10 scarecely has circumferential speed, the fluid makes virtually free swirl and therefore flows into labyrinth seals 6 and 7 at a reduced flow speed of the circumferential direction. Exciting force produced in the labyrinth seals 6 and 7 will then be reduced remarkably so that vibration of rotor can be prevented.

Static pressure gas bearing system

Abstract: PURPOSE:To improve the dynamic pressure rigidity in thrust direction of static pressure gas bearing system for dicer of semiconductor wafer by making a recess in axial direction in the thrust collar and communicating with a through- hole made through the thrust bearing. CONSTITUTION:Pressure air for supporting in radial direction to be fed through an air lead-in hole 31 and a radial bearing nozzle 32 into the gap between a tool spindle 1 and a sleeve 2 is discharged through the gap between a thrust bearing 4 and the tool spindle 1, recesses 41, 62, through-holes 46, 74 and the gap between a trust bearing 7 and the tool spindle 1. While pressure air in thrust direction fed to the trust bearing nozzles 44, 72 is discharged through the gap between a thrust plate 5 and the thrust bearings 4, 7, the recess 62 and the through-hole 74. With such structure, discharge is smoothed and the dynamic pressure rigidity in thrust direction can be improved.

Dynamic Pressure Calibration Standard

Abstract: A dynamic pressure calibration standard has been developed for calibrating flush diaphragm mounted pressure transducers Pressures up to 20 kPa (3 psi) have been accurately generated over a frequency range of 50 to 1800 hz The uncertainty of the standard is +/-5 pct to 5kPa (75 psi) and +/-10 pct from 5 kPa (75 psi) to 20 kPa (3 psi) The system consists of two conically shaped, aluminum columns, one 5 cm (2 in) high for low pressures and another 11 cm (43 in) high for higher pressures, each filled with a viscous fluid A column is mounted on the armature of a vibration exciter which imparts a sinusoidally varying acceleration to the fluid column Two pressure transducers mounted at the base of the column sense the sinusoidally varying pressure This pressure is determined from measurements of the density of the fluid, the height of the fluid, and the acceleration of the column A section of the taller column is filled with steel balls to control the damping of the fluid to extend its useful frequency range

Computation of Velocity and Pressure Variation across Axisymmetric Thick Turbulent Stern Flows.

Abstract: Many propellers and appendages are located inside of ship stern boundary layers. Therefore, it is essential for naval designers to obtain a fundamental understanding and accurate predictions of this special class of external thick turbulent stern flows. A series of experiments has been conducted at David W. Taylor Naval Ship R & D Center to determine the unique turbulence structure and viscous-inviscid interaction of thick axisymmetric [526–529] and simple three-dimensional [530–532] stern flows. The Lighthill [533] displacementbody concept has been proven experimentally to be an accurate approach for computing viscous-inviscid stern flow interaction. The measured static pressure distributions on the body and across the entire boundary layers were predicted by the displacement-body method to an accuracy within one percent of dynamic pressure.