Showing papers on "Dynamic pressure published in 1988"

Development and experimental test of an analytical model of the orifice pulse tube refrigerator

Abstract: The promise of high reliability and high refrigeration capacity is responsible for a recent surge of interest in pulse tube refrigeration. This work involves the development of an analytical model describing behavior of the orifice pulse tube to gain a better understanding of the refrigeration process. Due to oscillating gas flow, the system is described in terms of average enthalpy flow with such simplifying assumptions as an ideal gas and sinusoidal pressure variation. Phasor analysis is used to represent the temperature, pressure, and mass flow rate waves in vector form. Also discussed in this paper is the verification of the model in which analytical predictions are compared to experimental measurements. The results confirm predictions by the model that refrigeration power is proportional to the average pressure, the pulse frequency, the mass flow ratio, and the square of the dynamic pressure ratio. Also, a temperature probe was devised to measure the average temperature profile and dynamic temperature in the tube. As a result of simplifying assumptions, magnitudes of refrigeration power from the model are between 3 and 5 times greater than experimental values.

Wave-induced forces on buried pipelines

Abstract: Ocean waves induce dynamic pressure responses in permeable seabeds which result in dynamic loads on buried pipelines. An analytical model is developed for estimating the pore pressure in the soil and the resulting pressure force on buried pipelines. It is assumed that the seabed is rigid, homogeneous, and porous with isotropic permeability, that the pore water is incompressible, that fluid flow in the soil is modeled by Darcy's Law, and that the seabed is infinitely deep. A solution is developed for a circular, rigid pipeline using conformal mapping techniques. The solution is compared with the results of both small and large‐scale tests; reasonable agreement is obtained for the small‐scale tests. Wave‐induced seepage forces are evaluated by integrating the pressure distribution over the pipe surface. The magnitude of the force remains constant but the direction rotates around the cylinder once with the passage of each wave. This force may be of sufficient magnitude to be an important consideration in the...

Magnetic fields in the venus ionosphere: General features

Abstract: Analysis of the properties of the dayside ionosphere at Venus has shown that two situations are characteristic. One corresponds to the high dynamic pressure of the solar wind, and the other is realized at low dynamic pressure. In both regimes the ionopause manifests itself as a change of the dominant chemical component of plasma rather than the boundary of the magnetized and unmagnetized plasmas (the widely used definition). The nonstationary convection of the magnetized plasma in the Venus dayside ionosphere is analyzed qualitatively. It is argued that the observable large-scale magnetic field in the dayside ionosphere of Venus is the solar wind magnetic field pushed down into the ionosphere during the periods of high solar wind dynamic pressure which evolves under the action of convection and diffusion. The upper boundary of the magnetic belt forms in the vicinity of the upper boundary of the photochemical region. At low dynamic pressures of the solar wind, in a region from approximately 300 km to the ionopause, an upward flux of ionospheric plasma can exist due to motion of plasma to the terminator under the day-to-night pressure gradient. With the plasma convection and the results of the study of the Venus ionopause stability taken into account, the destruction of the large-scale ionospheric field is a probable source of flux ropes in the Venus lower ionosphere rather than small-scale ionopause instabilities.

Comparison of predictions and experimental data for hypersonic pitching motion stability

Abstract: The stability of oscillatory motions of vehicles flying at hypersonic Mach numbers is of considerable relevance to their initial design. Methods are needed for quick and accurate predictions of stability and control that are applicable over a wide range of body shapes, angles of attack, and flow conditions without the need to resort to computationally time-consuming numerical flowfield calculation methods. The purpose of this paper is to present experimental and theoretical data concerning the static and dynamic pitching stability of pointed and blunted 10 deg semiangle cones and a double-flared hyperballistic shape. Although Newtonian theory gives inadequate accuracy of prediction, inviscid embedded Newtonian theory, which accounts for the reduced dynamic pressure and lower flow velocity in the embedded flow downstream of the strong bow shock, is shown to provide surprisingly good agreement with experimental data over a wide range of conditions. Comparisons with experimental results show that the broad flow features associated with nose bluntness, angle of attack, and center of gravity position and their effect on static and dynamic stability are well described in regimes not containing flow structural change. However, in some cases discrepancies exist between the predictions and experimental observations, and these have been attributed to a variety of viscous-flow phenomena involving boundary-layer transition and flow separation, including complex lee-surface vortical flows.

Air flow metering terminal and control system

Abstract: A system for metering the flow rate of air through a duct in which gates are pivotally mounted and connected together to vary the area of the duct. The gates are balanced so as to be effectively weightless. The forces on and the position of the gates correspond to the pressure and the flow rate in the duct thereby avoiding the need for air pressure transducers exposed to the pressure in the duct. The forces due to the pressure in the duct are amplified by the gates so that the pressure measurement as a function of the forces on the gates is a much more sensitive function of the flow rate through the duct than is obtainable directly in response to the pressure in the duct (for example, the velocity pressure of air as measured by pressure transducers responsive directly to the velocity pressure in the duct). A computer system is responsive to the position of the gates and to the magnitude of an actuating signal (the fluid pressure applied to an actuating cylinder coupled to the gates) for determining the air flow rate and for varying the actuating signal in order to control the area in the ducts between the gates so as to obtain a desired air flow rate. 7

Perturbation pressure at the base of cumulus clouds in low shear

Abstract: We examine the pressure fields wound the cloud-base updraft of three cumulus clouds observed in environments with low vertical shear of the horizontal wind near cloud base. These fields are compared to the corresponding pressure fields beneath convective clouds embedded in moderate to large shear. All of the pressure fields are derived from aircraft measurements taken during the 1981 Cooperative Convective Experiment, CCOPE. The pressure fields associated with these low-shear clouds are weaker than those for the clouds in higher shear. Furthermore, the low-shear fields are not consistently dominated by the dynamic pressure created by the interaction of the cloud-base updraft with the vertical shear of the horizontal wind. The weaker dynamic pressure is due to the smaller size and intensity of the cloud-base updraft as well as the smaller vertical shear of the horizontal wind. The reduction of the dynamic Pressure allows buoyancy effects on the pressure field to become more apparent.

Fluid additive injector

Abstract: A system which combines an additive storage vessel and mixing section containing pressure and suction taps off of a main transfer tube. This allows controlled blending of additive into a fluid stream without external energy or controls. The tank is shaped to allow a stratified layer of fluid to slowly displace the additive. Displacement energy is supplied by a positive pressure tap facing into the flow converting dynamic pressure of fluid flow into increased static pressure and a reduced pressure tap created by facing with the stream flow. Trickle tubes connect the taps to opposite ends of the additive charge, which is slowly pushed and pulled into the fluid stream. Rate of additive supply can be controlled by restrictors, tap orientation or tank orientation. An air relief valve is provided to allow escape of non-pressurized air from tank.

Vessel speed detecting device

Abstract: A vessel speed indicating device including a semiconductor pressure detector that detects dynamic pressure and outputs a signal indicative of this pressure. A speed indicator and calculator is incorporated which senses when the speed is below a speed at which high accuracy can be expected and outputs a warning signal in the event of that condition. Alternatively, when the device is operating in a range where the speed signal is accurate, actual speed is indicated.

Nondimensional Pressure Responses of Pneumatic RC Circuits Considering Heat Transfer

Abstract: Dynamic characteristics of pneumatic RC circuits is the basis for many fundamental pneumatic circuit dynamics. This paper describes dynamic pressure response of pneumatic RC circuits with nondimen sional equations, considering the heat transfer effect. Pressure response of pneumatic RC circuits is affected by the heat transfer effects between the air in the chamber and chamber wall. From this viewpoint, thermal-time constant and pressure-time constant are derived. With nondimensional parameter, which is the ratio of two time constants, pressure and temperature responses can be analyzed. The experimental data are in satisfactory agreement with the calculated pressure and temperature responses.

Description of an oscillating flow pressure drop test rig

Abstract: A test rig designed to generate heat exchanger pressure drop information under oscillating flow conditions is described. This oscillating flow rig is based on a variable stroke and variable frequency linear drive motor. A frequency capability of 120 hertz and a mean test pressure up to 15 mPA (2200 psi) allows for testing at flow conditions found in modern high specific power Stirling engines. An important design feature of this rig is that it utilizes a single close coupled dynamic pressure transducer to measure the pressure drop across the test sample. This eliminates instrumentation difficulties associated with the pressure sensing lines common to differential pressure transducers. Another feature of the rig is that it utilizes a single displacement piston. This allows for testing of different sample lengths and configurations without hardware modifications. All data acquisition and reduction for the rig is performed with a dedicated personal computer. Thus the overall system design efficiently integrates the testing and data reduction procedures. The design methodology and details of the test rig is described.

Influence of Pressure Gradient upon Boundary Layer Stability and Transition

Abstract: The present paper deals with the effect of adverse pressure gradient on boundary layer stability and transition in an incompressible fluid qualitatively as well as quantitatively. In order to produce various kinds of pressure gradients along a flat plate located horizontally, the cross sectional area of the working chamber is varied by the vertical side walls. Changes in velocity profiles and in intensity of streamwise velocity fluctuation in a boundary layer are measured in the transition region. The distribution of dynamic pressure at 0.43 mm from the surface is correlated with that of intensity of velocity fluctuation. Moreover, transition length is correlated with a shape parameter. Further, the process of transition is shown to be different from the case of zero pressure gradient when the half included angle is 3.6 degree. Finally, mention is made of the relation between transition Reynolds number and a characteristic frequency from the standpoint of linear stability theory.

Apparatus for measuring flow rate and pressure

Abstract: PURPOSE:To simplify the measurement of a mass flow rate, by making it possible to simultaneously measure the flow rate and pressure of a fluid when the temp. of the fluid is constant. CONSTITUTION:When a fluid flows through a pipe body 9, the pressure due to the dynamic pressure of the fluid acts on a pressure receiving plate 4 in a flow direction. Since a hose 12 has almost no restriction force in an up-and- down direction, the force FP due to the pressure P of the fluid acts on the disc part 11 of a T-shaped arm 1. When the pressure receiving area of the disc part 11 is assumed to be S, the force FP becomes FP=P.S. From the foregoing, when forces acting on two load sensors 5, 6 are set to FA, FB, relations FA+FB=FP=P.S and (FB-FA)l1=Fd.l2 hold by considerity the balance for force and moment. By this method, when the forces FA, FB acting on two load sensors 5, 6 are measured, the pressure P and velocity V of flow are obtained and a flow rate is calculated from the velocity V of flow and the inner diameter of a pipe body 9.

Silencing method in gas conducting devices with variable dynamic pressure in the flow, especially in exhaust devices of internal-combustion engines

Abstract: In a method for silencing exhaust systems of internal-combustion engines, having a throttling of the exhaust system as a function of at least one operating parameter of the internal-combustion engine, it is proposed that the exhaust system be throttled only during positive pressure amplitudes of the dynamic exhaust-gas pressure fluctuations, and in synchronism with the frequency of these pressure amplitudes.

Man type chute active and static pressure mixed air bearing

Abstract: The utility model relates to a man type chute active and static pressure mixed air bearing, belonging to the field of gas bearing. The utility model provides a gas bearing which requires low machining precision and can be used widely, and has the advantages of simple structure, convenient assembly and disassembly, and high capability and stability. The man type chute active and static pressure mixed air bearing is characterized in that axis have pumping man type grooves; the filtering external pressure bearing is used to supply air, which makes the bearing have both dynamic pressure effect and static pressure effect. The bearing has the advantages of little air consumption, and with the slit or multiporous material restrictor used to supply air, the problems of the start-stop of the self-action groove bearing and preventing dust from going into the bearing can be solved. The utility model can be used for the field of turbomachinery, gyro, etc.

Interaction of Wind Waves With Vertical Wall

Abstract: A modification of the linear wave theory of the interaction between wind‐induced waves and an infinite vertical wall is presented. As the free surface fluctuates with time, a point fixed in space in the vicinity of the mean water level is not submerged at all times but emerges from the water in some phases of the wavy motion. The modification consists of taking into account this effect, which is referred to in this paper as the emergence effect. Its influence is essential when determining the stochastical characteristics of pressures and forces on the vertical wall. Numerical results for the mean value and variance of the dynamic pressure and force induced by wind waves are obtained and presented graphically. Comparisons are made with the case in which the free surface fluctuation phenomenon is ignored. Inclusion of the free surface fluctuation phenomenon appreciably changes the mean value and variance of the pressure and force relative to the unmodified theory. The difference is most pronounced at points...

Coolant fluid supply device

Abstract: PURPOSE:To surely clean a chip to be removed, by mounting a pressure increasing device, which generates a water hammer phenomenon by a blocking member intermittently opening and closing a return passage, to be interposed in a coolant fluid supply passage, in the case of a boring device. CONSTITUTION:Coolant fluid is allowed to flow into a high pressure chamber 18 of a pressure increasing unit 2 from a feed passage 4 by a volute pump and partly into a low pressure chamber 17 via a communication path 19 because a blocking member 22 is opened by a spring 26, and a supply device, filling a damper part 22c with the fluid through a groove 21c of a protruding member 21, returns the fluid to a storage tank from a passage 6. While the rest of the fluid is fed to a boring tool via a high pressure passage 5. If the predetermined time passes after the pump is operated, the supply device, increasing a flow speed of the coolant fluid to increase its dynamic pressure, moves the blocking member 22 to the right, till it closes the groove 21c, rapidly increasing pressure in the high pressure chamber 18 to generate water hammer, while if its reflective wave causes the pressure in the high pressure chamber 18 to decrease, the supply device moves the blocking member 22 to the left by a pressure in the damper part 22c, thus repeating the action in the above. In this way, the device well performs cooling of the boring tool, removal of a chip and washing.

Fluid measuring instrument

Abstract: PURPOSE:To measure pressure and temperature simultaneously at the same place and to calculate the mass, etc, of fluid by using a diffusion type semiconductor sensor CONSTITUTION:The diffusion type semiconductor sensor 16 is constituted by forming a bridge circuit of four diffusion gauge resistances 20 on a silicon substrate 18 and detects pressure This sensor 16 is arranged against a flow of fluid and a constant current is supplied 22 to both ends of the resistances 20 Then if there is a flow fluid at the periphery of the sensor 16, piezoelectric resistance effect is caused according to the flow velocity and the value of the resistances 20 varies The terminal voltage across the bridge impedance and bridge unbalanced voltage vary according to said variation and those are amplified 26 and 28, A/D-converted 31, and inputted to a CPU 32 Consequently, the CPU 32 obtain the pressure and temperature of the fluid from the respective voltages to perform temperature compensation and sensitivity compensation, and then computes accurate dynamic pressure, thereby obtaining density from a specific table Then, those values are substituted in a specific expression and the square root of the values is computed to find the mess flow rate of the fluid, which is outputted

Pressure control device, especially for pressure medium-actuated brake systems of motor vehicles

Abstract: A pressure control device is proposed with a control valve arranged in a housing (1) between an inlet (10) and an outlet (11), which valve is provided in a control piston (2) which is displaceable as a function of the pressure against a control force, with an inertial body (4), movable as a function of the acceleration, which actuates a control piston (3). In order to create a pressure control device which is cost-effective to manufacture and to assemble, and which has a dynamic pressure characteristic curve, it is proposed that, between the control piston (3) and the valve seat (45) of the inertial body (4), a pressure chamber (62) be connected to the main bore, the volume of which is adjustable against the force of elastic means.

Method and device for monitoring surging of axial flow compressor

Abstract: PURPOSE:To detect surging effectively by determining the Mach number and pressure factor on each operating occasion, comparing with the set value of pressure factor at the current Mach number, and thereby judging the degree of surging. CONSTITUTION:During the compressor being in operation, the dynamic pressure around inlet to strings of vanes and the Mach number are measured using a Pitot tube 5, and at the same time, the static pressure on the surface of a stator vane 4' is measured. A control device 8 selects the set value of pressure factor corresponding to the fed measurement of the Mach number to be subjected to comparison with the fed pressure factor. The degree of the obtained value from comparison serves judgement to know how much margin is reserved to surging.

Karman type air flow rate sensor

Abstract: PURPOSE:To increase an output amplitude and to accurately detect an air inflow by installing a connecting pipe which is open in an air inflow direction behind the side part of a vortex generation body CONSTITUTION:The connecting pipe 11 which is open in the air inflow direction is installed behind the side part of the vortex generation body 1 consisting of a prismatic edge and a trapezoid block behind it Thus, the connecting pipe 11 is provided at the position like this and then there is influence of not only the static pressure in a pressure variation area 5, but also dynamic pressure based upon the current velocity of an air flow, so the amplitude of variation in pressure is increased by a quantity corresponding to the dynamic pressure Consequently, the generation frequency of a vortex is detected by a pressure sensor 12 with good sensitivity and the air inflow is detected with high accuracy

Dynamic pressure fluid bearing device

Abstract: PURPOSE:To decrease the rotating speed to start floating in the thrust direction and shorten the time to attain the stationary flotation quantity by providing a pressure regulating valve on a flow hole communicating a pressure chamber formed between the end face of a shaft and the thrust bearing face to the outside of a housing. CONSTITUTION:A flow hole 11 is provided at the center of the thrust bearing bottom 3 of a housing 1, and a pressure regulating ball 12 is brought into contact with it. When the housing 1 is rotated, the housing 1 is floated by the action of the dynamic pressure generating groove 5 of a shaft 4. During the low-speed rotation, the ball 4 is kept in contact with the flow hole 11, the fluid does not flow out, and the housing 1 is floated at a lower rotating speed. When the rotating speed is increased and the dynamic pressure is made larger than the energizing force of the ball 12, the fluid flows out, and the flotation quantity of the housing 1 becomes a fixed value. Therefore, the rotating speed to start floating is decreased and the time to attain the stationary flotation quantity is shortened by regulating the pre-load by the ball 12.

Oscillating vane for measuring speed of gas flow

Abstract: Experiments with an oscillatory vane in a wind tunnel reveal that the vane’s oscillation frequency is directly proportional to the square root of the dynamic pressure of the flow. The linear relationship is observed for flow speeds up to the speed of sound in air, argon, and helium. The vane’s oscillations are a measure of mass flow, or if used on an aircraft, of indicated air speed. In constant density media the oscillation frequency is directly proportional to flow speed, and a simple count of the oscillations is a measure of distance traveled. At given ambient temperature and pressure, the vane’s frequency is the same at the speed of sound for all gases, irrespective of their molecular weight.

Head for magnetic recording and reproducing device

Abstract: PURPOSE:To prevent spacing loss due to the increase of relative velocity from being increased, by setting the position of a read/write gap in a specific range on the outflow end of a sliding part assuming the length of the sliding part in the inflow/outflow direction of gas as one. CONSTITUTION:When a disk 1 is rotated and is moved in a direction of arrow head G for a head, the head 10 floats by a dynamic pressure effect due to air compression generated between the head 10 and the disk. At this time, a gap quantity between the head and the disk is distributed in a state where the quantity on the inflow side of the head is larger than that on the outflow side. And relation (h1

Wake-induced unsteady aerodynamic interactions in a multistage compressor

Abstract: The effects of steady loading and the detailed aerodynamic forcing function on airfoil row unsteady aerodynamics are investigated and quantified at high reduced frequency values. For the first time, both parallel and normal gust components of the forcing function are considered. This is accomplished by a series of experiments that quantify the unsteady aerodynamics of the first stage vane row of a research compressor. The effects of steady vane aerodynamic loading with both nonconstant and constant aerodynamic forcing functions are quantified. These data show that the steady loading affects only the magnitude of the complex dynamic pressure coefficient, whereas the ratios of the maximum amplitudes of the parallel and normal components of the aerodynamic forcing function affect both the magnitude and the phase lag. The relative effects of the two components of the time-variant inlet velocity field on the resulting vane row unsteady aerodynamics are also investigated, showing that the parallel component of the aerodynamic forcing function affects only the dynamic pressure coefficient phase lag. The correlation of the dynamic pressure coefficient data with flat plate predictions is also considered. The level and chordwise distribution of the steady aerodynamic loading, not the incidence angle, are revealed to be the key parameters to obtain good correlation with such mathematical models.

Measurement of dynamic pressure aronud the vane in an oil hydraulic vane pump.

Abstract: Measurements of the dynamic internal pressures near the vane of a pressure balance type of an oil hydraulic vane pump with intravanes have been made to provide essential information for the study of the pump dynamics and control, the pump design and the analysis of tribological problems in the sliding components. The influences of the discharge pressure and rotating speed of the vane on the dynamic pressure in four chambers surronding a vane have been investigated. The results indicate that the surge pressures of the chambers at the instant of the start of discharge and closure are affected by the rotating speed, and the pressure in the intravane chamber maintains approximately constant values with marked effect of pulsating discharge pressure.

Pressure gradient determination by three dimensional Doppler ultrasound using a modified Bernoulli equation

Abstract: Three-dimensional Doppler ultrasound was used to determine pressure gradients in an in vitro model of a velocity jet. Doppler velocity determinations were within 3.85% of actual velocities, and the pressure gradients predicted by these velocities were within 2.85% of the pressures predicted by the Bernoulli equation. A proposed modification of the Bernoulli equation was used to account for the differences between pressures predicted by the theoretical Bernoulli equation and the actual measured pressures, which varied by as much as 16.86%. The modified Bernoulli equation contains a first-order term in velocity, derived from the Navier-Stokes equations, to estimate the frictional loss in a circular tube. The application of a modified Bernoulli equation is discussed for predicting degree of stenosis in clinical applications. >