Showing papers on "Dynamic pressure published in 1995"

Techniques for the determination of local dynamic pressure and angle of attack on a horizontal axis wind turbine

Abstract: Surface pressure data from the National Renewable Energy Laboratory`s ``Combined Experiment`` were analyzed to provide a statistical representation of dynamic stall occurrence on a downwind horizontal axis wind turbine (HAWT) Over twenty thousand blade rotational cycles were each characterized at four span locations by the maximum leading edge suction pressure and by the azimuth, velocity, and yaw at which it occurred Peak suction values at least twice that seen in static wind tunnel tests were taken to be indicative of dynamic stall The occurrence of dynamic stall at all but the inboard station (30% span) shows good quantitative agreement with the theoretical limits on inflow velocity and yaw that should yield dynamic stall Two hypotheses were developed to explain the discrepancy at 30% span Estimates are also given for the frequency of dynamic stall occurrence on upwind turbines Operational regimes were identified which minimize the occurrence of dynamic stall events

Energy dissipation in oscillatory flow within a baffled tube

Abstract: Pressure fluctuations and rates of energy dissipation have been measured for sinusoidal oscillatory flow of light oil in a tube equipped with a series of wall baffles. A laboratory shell-and-tube heat exchanger was fitted with a single length of 1.0 m, 12 mm internal diameter tubing containing 55 orifice-type wall baffles. The frequency of oscillation was varied in the range 3 to 14 Hz, and the amplitudes (centre to peak) in the range 1 to 6 mm. The pressure/time characteristics show that the pressure variation leads the velocity variation by a phase angle which decreases as frequency is increased. The power dissipation measured for oscillatory flow agrees with the well-known quasi-steady model at large amplitudes, but at lower amplitudes and higher frequencies the predictions of quasi steady theory are exceeded by a significant degree. A new flow model is proposed, based on acoustic principles and the concept of eddy viscosity. The model contains two adjustable parameters; the mixing length (approximately equal to the orifice diameter), and a correction factor for the fluid inertia. This model is able to predict the dynamic pressure response and the overall power dissipation rate with reasonable accuracy

Air data system for measuring fluid flow direction and velocity

Abstract: The invention is a system for determining the physical characteristics of an incident fluid flow stream over a surface of a vehicle relative to an axis thereof, the apparatus. In detail, the invention includes at least one first pressure sensor mounted on the surface, the at least one first pressure sensor for receiving dynamic pressure signals generated by the convected boundary layer of the fluid flow stream and providing an output signal representative thereof. At least one array of second pressure sensors (pressure transducers) is positioned down stream of the at least one first pressure sensors, the second sensors of the at least one array each of said second pressure sensors providing a second output signal representative of the above pressure signals received thereby. A computer system is adapted to receive the first and second signals and to calculate the angular direction of the fluid flow relative to the axis and the velocity thereof.

k-factors for HVAC ducts: Numerical and experimental determination:

Abstract: A new method for determining the velocity pressure loss factor (k-factor) of HvAC duct fittings has been established The method presented here is based on computational fluid dynamics (CFD) and experimental measurements The constant-injection tracer-gas technique and a pitot tube were used to measure mean air velocity in a square duct with bends Pressure distribution along the duct was measured using static pressure tappings The k-factor was calculated from the measured pressure loss and air velocity for the duct fitting CFD was used to predict airflow and pressure distribution in the duct It was found that the accuracy of the prediction depends on the turbulence model and differencing scheme used Optimum predictions of pressure loss and k-factor were achieved using CFD with a combination of the standard k-e turbulence model and quadratic upstream interpolation scheme The predicted k-factor was in good agreement with experimental results

Mixing and Chemical Kinetics Interactions in a Mach 2 Reacting Flow

Abstract: An experimental study of transverse hydrogen injection and combustion behind a rearward-facing step into a Mach 2 airflow was conducted in an electrically heated (not vitiated), continuous-flow facility to evaluate the effects of initial conditions (temperature, pressure, and equivalence ratio), and analyze the interactions between mixing and combustion in supersonic, reacting flows. Neither mixing nor reaction rates dominate in this particular regime, thus the use of initial conditions to scale fuel mixing (i.e., dynamic pressure ratio) has to be modified by a descriptor that includes the effects of combustion on the flow conditions at the fuel injection station. Combustor inlet static pressure was varied from 0.25 to 0.5 atm, and total temperature from 300 to 850 K. Injector configurations include both single and staged injection with injectors of 1 and 1.5 mm diam, transverse to the airflow, behind a 5-mm rearward-facing step. Images of visible flame emission distribution at several temperatures correlated with pressure and temperature measurements are used to describe the coupling between fluid dynamics and chemical kinetics, discussed in terms of a characteristic global Damkohler number (ratio of chemical reaction rate to turbulent mixing rate). A proposed modification to mixing scaling with dynamic pressure ratio in the presence of heat release effects is presented.

Measurement and analysis of static pressure field in a torque converter pump

Abstract: In this paper, the static pressure field and performance parameters of a torque converter turbine are measured, analyzed, and interpreted under three speed ratio conditions (0, 0.6, and 0.8). A proven measurement technique was developed for the steady-state measurement of static pressures in the turbine. Results show that: (1) the static pressure field is generally poor at the core section; (2) centrifugal force has the dominant effect on the static pressure drop in the turbine at SR = 0.6 and SR = 0.8; and (3) the static pressure loss due to viscous effects and due to the diffusion of the relative velocity is very pronounced at SR = 0.

A linear perturbation analysis of magnetopause motion in the Newton-Busemann limit

Abstract: The response of the magnetopause surface to time-varying solar wind dynamic pressure is examined. We argue that to a first approximation the magnetopause surface may be considered as analogous to an elastic membrane. Upon displacement from equilibrium resulting from a change in applied external pressure, it moves to a new equilibrium under the equation of motion of a forced, damped, simple harmonic oscillator. We derive this equation of motion by linearising for small perturbations the momentum equation for flow past a nonrigid ellipsoidal body in the Newton-Busemann limit. Though our approach is only an approximation to the real dynamics of the magnetopause boundary, it serves to demonstrate the importance of inertia in the system response. It allows us to estimate the natural eigenperiod of magnetopause oscillation as typically around 7 min, the precise value depending on solar wind conditions. However, the magnetopause eigenoscillation is furthermore found to be strongly damped, regardless of solar wind conditions. One consequence of these properties is that short-period fluctuations in the solar wind dynamic pressure elicit a suppressed magnetospheric response. We outline other theoretical expectations by which our model may be tested against observation, and discuss the implications of our findings for current interpretations of spacecraft observations made in the dynamic magnetopause environment.

Pressure‐pulse driven surface waves at the magnetopause: A rebuttal

Abstract: A variety of mechanisms have been proposed to account for transient events observed in the vicinity of the dayside magnetopause. Discriminating among the various proposed mechanisms is a key objective of magnetospheric physics but requires careful consideration of their predictions. Song et al. (1994) recently reported the results of an effort to determine the characteristics of transient events produced by variations in the solar wind dynamic pressure. Noting that the observed characteristics did not coincide with those they predicted, they concluded that transient events in the vicinity of the dayside magnetopause could not be caused by solar wind dynamic pressure variations. In this rebuttal, we call attention to our previous work concerning the expected characteristics of transient events produced by variations in the solar wind and foreshock pressure ; that work uses more realistic parameters to conclude that the transient events are consistent with a solar wind/foreshock pressure mechanism.

Effect of Pressure Wave Form on Pulse Tube Refrigerator Performance

Abstract: We have constructed a pulse tube refrigerator (PTR) test apparatus that can be operated in different modes: as basic, orifice-, or double-inlet-type PTR. A special motor driven multi channel rotary valve in combination with needle valves serves to control the Helium gas flow between compressor and refrigerator inlets. With dynamic pressure and temperature sensors at various positions and a calibrated heat input at the cold end the cooling performance of the refrigerator was studied systematically under various working conditions, such as frequency and amplitude of the pressure wave and the settings of the orifice and second inlet flow. Keeping constant the average mass flow through the rotary valve, particular attention has been directed towards a possible effect of the shape of the pressure wave. A minimum temperature of 42 K has thus far been achieved with double inlet configuration using a frequency of 2.1 Hz, an average pressure of 21 bar, a high to low pressure ratio of 1.32, an average mass flow rate through the rotary valve of 1.0 g/s, and an approximately trapezoidal wave form. Under these conditions, the net cooling power at 80 K is Q = 2.5 W. With a higher pressure ratio of 1.5, corresponding to an average mass flow of 1.56 g/s, Q = 4 W at 80 K is obtained at the expense of a higher no-load temperature of 52 K. In all three modes of operation the net cooling power varies linearly with cold end temperature. For orifice and double-inlet configuration the measured slopes dQ/dT are in qualitative agreement with the enthalpy flow theory of Radebaugh et al.. A significant effect of the pressure wave form on the minimum temperature and the temperature profile along the pulse tube has been observed. While holding all other parameters constant, the minimum temperature increases markedly when the dwell times at high or low pressure are reduced. Regarding high cooling power, the optimum wave form is characterized by a long dwell time at high pressure, which may be ascribed to an increased heat transfer to the hot heat exchanger.

Energy deposition in the cathode layer of transient high pressure glows derived from interferograms of the emanating pressure wave

Abstract: The large electric fields in the cathode sheath of high pressure glow discharges lead to localized energy deposition in the gas, which drives a gas dynamic pressure wave into the region where the transient high pressure glow is homogeneous. For a range of parameters typical for discharge pumped XeCl‐lasers the gas density profiles of these waves have been measured interferometrically with high spatial resolution (20 μm). From comparisons with gas dynamic model calculations the amplitude and the spatial profile of the initial temperature distribution resulting from the energy deposition during the formation of the cathode sheath have been determined. These data can be used to verify assumptions to be made in future improvements of self consistent discharge models of the cathode sheath formation.

User manual for NASA Lewis 10 by 10 foot supersonic wind tunnel

Abstract: This manual describes the 10- by 10-Foot Supersonic Wind Tunnel at the NASA Lewis Research Center and provides information for users who wish to conduct experiments in this facility. Tunnel performance operating envelopes of altitude, dynamic pressure, Reynolds number, total pressure, and total temperature as a function of test section Mach number are presented. Operating envelopes are shown for both the aerodynamic (closed) cycle and the propulsion (open) cycle. The tunnel test section Mach number range is 2.0 to 3.5. General support systems, such as air systems, hydraulic system, hydrogen system, fuel system, and Schlieren system, are described. Instrumentation and data processing and acquisition systems are also described. Pretest meeting formats and schedules are outlined. Tunnel user responsibility and personnel safety are also discussed.

High speed rotor assembly

Abstract: A ring-shaped magnet (19) is bonded to an outer circumferential portion of a rotary body (21) supported on a rotary shaft (13) which forms a radial dynamic gas pressure bearing. A ring-shaped magnet (23) is provided with a predetermined distance maintained between itself and the ring-shaped magnet (19). Owing to the magnetic attractive force of these two ring-shaped magnets (19, 23), the rotary body (21) is restricted in its axial movement and held radially rotatable. Since the rotary body (21) is held in a 0.5 decentered state due to the difference in the magnetic balance between the ring-shaped magnets (19, 23), the radial dynamic gas pressure bearing generates a high dynamic pressure. A high dynamic pressure occurs due to herringbone dynamic gas generating grooves (15a, 15b) as well. Owing to the synergetic effect of these parts, a very high radial load capacity occurs, and the rotational accuracy is improved.

Unsteady Pressure Measurement in a High Temperature Environment Using Water Cooled Fast Response Pressure Transducers

Abstract: Measurement of unsteady pressure is a requirement in many proposed aero-engine active control systems. In the high temperature environment associated with the engine, thermally unprotected transducers may not measure accurately or even survive. This paper reports an examination of two water cooled, commercially available unsteady pressure transducers, which assesses the ability of the transducer to accurately measure unsteady pressure when mounted in a water cooling adapter and the effectiveness of the thermal protection at high temperatures.Mounting the transducer in a cooling adapter was shown to have no adverse effect upon its ability to measure dynamic pressure. Deliberately recessing the adapter back from the flow provided the most stable and predictable output at all flow conditions tested. Thermal protection allowed the transducer to survive at flow temperatures of up to 500°C with a potential to survive at higher temperatures. No reduction in performance is shown at elevated temperatures relative to performance at ambient conditions.Copyright © 1995 by ASME

Measurement of gust response on a turbine cascade

Abstract: The paper presents benchmark experimental data on a gust response of an annular turbine cascade. The experiment was particularly designed to provide data for comparison with the results of a typical linearized gust-response analysis. Reduced frequency, Mach number, and incidence were varied independently. Except for the lowest reduced frequency, the gust velocity distribution was nearly sinusoidal. For the high inlet-velocity series of tests, the cascade was near choking. The mean flow was documented by measuring blade surface pressures and the cascade exit flow. High-response pressure transducers were used to measure the unsteady pressure distribution. Inlet-velocity components and turbulence parameters were measured using hot wire. In addition to the synchronous time-average pressure spectra, typical power spectra are included for several representative conditions.

Aerodynamic pressure spindle device

Abstract: PURPOSE:To provide an aerodynamic pressure spindle device that is able to widely cope with various machining modes different in rotation speed of a main spindle as this main spindle is provided with sufficient rigidity even in any rotation speed ranging from low speed rotation to the high speed one. CONSTITUTION:This spindle device is composed of a spindle 1 rotating as connected to a driving means, a radial aerodynamic pressure bearing 3 being installed in and around this spindle 1 and supporting a shaft 1 on a housing 2 free of rotation, and a thrust aerodynamic pressure bearing 4 being installed in and around the spindle 1 and regulating a movement of the shaft 1 in the axial direction. In this constitution, a static pressure generating recess on the same surface with a dynamic pressure generating groove and to be interconnected to this groove is formed in both these radial and/or thrust aerodynamic pressure bearings 3 and 4, and further a static pressure imparting means 10 imparting static pressure to these bearings 3 and 4 is installed there, whereby rotation of the spindle 1 is supported as making those of static pressure and dynamic pressure work together.

Inviscid analysis of transonic oscillating cascade flows using a dynamic mesh algorithm

Abstract: A locally implicit total-variation-diminishing scheme and a rigid-deformable dynamic mesh algorithm are formulated on the quadrilateral-triangular meshes. The unsteady Euler equations with moving domain effects are solved in a Cartesian coordinate system. For transonic flows around an oscillating cascade of four biconvex blades with different oscillation amplitudes, reduced frequencies, and interblade phase angles, the calculated distributions of magnitude and phase angle of the first harmonic dynamic pressure difference coefficient agree better with experimental data than those from linearized theory and related numerical results on triangular meshes in most of the cases. Also, the numerical wiggles of instantaneous blade surface pressure coefficient distributions, which appeared on the triangular meshes, are eliminated. From the instantaneous pressure and Mach number contours, the unsteady flow phenomena, such as periodical characteristics, pressure wave and shock behaviors, and time-variations of zones with high Mach number gradient normal to the blade surfaces, are investigated. Furthermore, the lift coefficient distributions indicate that the oscillation .amplitude, reduced frequency, and interblade phase angle all have significant effects on the transonic oscillating cascade flows.

Dynamic pressure bearing and manufacture thereof

Abstract: PURPOSE: To form a dynamic pressure plane and a dynamic pressure generation groove efficiently at a predetermined accuracy CONSTITUTION: A shaft body 21 and a shaft fitting body 31 constituting a dynamic pressure plane are made of aluminum or an alloy thereof excellent in machinability Both the dynamic pressure planes 21, 31 and a dynamic pressure generating groove 25 are formed by cutting using a same cutting machine without requiring any mounting/demounting With such method, both the dynamic pressure planes 21, 31 and the dynamic pressure generating groove 25 can be formed well without decrease of the machining accuracy COPYRIGHT: (C)1996,JPO

Exploratory Analysis of Helium Layer Usage for Dynamic Pressure Enhancement in the Large Blast/Thermal Simulator.

Abstract: : Numerical simulations of the time dependent flow in the Large Blast/Thermal Simulator (LB/TS) were executed to model a possible use of that facility for enhancing dynamic pressure using a helium layer positioned on the floor of the expansion tunnel. The simulations were performed using a 2-D, finite difference Euler equation solver with multiple material models. The flow structure and recorded flow history data for the simulation, employing a single helium layer, are compared to the results of a calculation without a helium layer in order to quantify the dynamic pressure enhancement produced by the presence of the helium layer. The results of the calculations show that the greatest enhancement in dynamic pressure impulse is approximately a factor of two over the case with no helium layer but is limited to a region less than 1 meter from the floor of the expansion tunnel. This limited region of dynamic pressure enhancement is insufficient for blast testing of full scale military vehicles and equipment.

Dynamic pressure gas bearing and its manufacture

Abstract: PURPOSE:To provide a high-speed, high-precision dynamic pressure gas bearing which can be increased in radial bearing rigidity by using compressive effect inherent in a dynamic pressure gas film, stabilized at a high speed and reduced in unbalanced vibration. CONSTITUTION:Recesses A1-A3 and protrusions B1-B3 with regular cycles in the peripheral direction are formed on the contour of a fixed shaft 3, and one cycle from the starting points to the finishing points of the recesses A1-A3 and the protrusions B1-B3 is constituted by harmonious waveforms.

Pi-slot dynamic and hydrostatic mixed gas bearing

Abstract: A pi-shaped slot dynamic and static pressure mixed type gas bearing belongs to the technical field of gas bearings. The gas bearing provided by the utility model has the advantages of high bearing capacity, high stability, simple structure and wide application. The utility model is characterized in that a pi-shaped slot is arranged on the surface of a rotating shaft, a filtered external pressure bearing is used for supplying gases, and thus, the bearing has two effects of dynamic pressure and static pressure. The bearing has the advantages of better pumping effect and high bearing capacity, and is especially suitable for rotary machines with high speed and heavy load.

The flow reference system-an air data system for wind tunnels

Abstract: The paper describes an integrated system specifically developed for establishing the elementary flow quantities Total Pressure (P/sub t/), Static Pressure (P/sub s/), and Total Temperature (T/sub t/) in a windtunnel environment with the highest presently attainable accuracy. These quantities are required for calculating quintessential aerodynamic parameters like Mach number (Ma), Dynamic Pressure (Q), Reynolds number (Re), and Flow Velocity (V). Up to four extremely accurate (0.015% Full Scale) absolute or differential Pressure Sensing Units can be accommodated on a plug-in basis in this "Flow Reference System". Temperature measurement is based on the use of a Platinum 100 ohm RTD sensor; accuracy of signal conditioning and linearization are better than 0.05/spl deg/C over a range of -200 to +100/spl deg/C. Data output for pressures and temperature is in fully corrected Engineering Units over two independent output links at a high sampling rate of 10 Hz. A status word output allows an effective monitoring of system integrity. The concept was originally developed by the European Transonic Windtunnel GmbH for application in their High-Reynolds number cryogenic facility, but the flexible, modular approach makes it an attractive proposition for any windtunnel. The implementation is based on the 5400 System Processor (SP) of Pressure Systems Inc. (PSI). The paper discusses the design considerations including an accuracy analysis, and presents details of the practical realization. Some results are given based on two years of operational experience.

Turbine expansion machine

Abstract: PURPOSE:To provide a turbine expansion machine which prevents a dynamic pressure type thrust gas bearing part from burning and occurrence of any accident following by its burning. CONSTITUTION:A turbine expansion machine is provided with a first pressure detector 1 to detect pressure for the outlet part 21 of a turbine impeller 11, a second pressure detector 2 to 7 detect pressure for the inlet part 22 of a blower impeller, and a controller 3 to output signals which calculate thrust force for acting from signals detected from the first and second pressure detectors 1, 2 to a rotary axis 13 and make a opening/closing valve 27 in opening condition when this thrust force exceeds a predetermined value.

Locking device fixing two mutually relative displaceable body

Abstract: PURPOSE: To faciliate stepless interlock by enabling two components capable of relatively sliding against each other after they have slid to the outside from a static position to open a fluid connection. CONSTITUTION: When a piston rod 3 makes axial sliding force of a sealed element 9 become larger than bearing force of a preparatory element 11 by additional tension, the sealed element 9 is separated from a sealed position to lose sealing function, and hydraulic fluid flows in a space between a piston 6 and a component 7 from a hydraulic chamber 4 through a fluid connection 17. After the hydraulic fluid flows into a hydraulic chamber 5 through a hole 14, chain lock pressure in the hydraulic chamber 4 is reduced to low dynamic pressure, and the dynamic pressure continuously holds the component 7 in regard to the larger fluid-pressure surface B of the component 7. When the hydraulic chambers 4 and 5 are connected to each other through the fluid connection 17 and hole 14, the fluid connection 17 is sealed by the sealed element 9 in this position. After initial high chain lock force is overcome, the piston rod 3 can be adjusted by small adjusting force, and when the motion of the piston rod is stopped, pressure compensation can be made between the hydraulic chambers 4 and 5.