Showing papers on "Dynamic pressure published in 1977"

Fluctuating Pressure Environment of a Drag Reduction Spike

Abstract: Wind-tunnel measurements have been made of the fluctuating pressure environment in a region of spikeinduced flow separation. Extremely large pressure fluctuations (30% of freest ream dynamic, pressure) were measured on the sides of the spike base at transonic speeds which are related to the nonaxisymmetric, vortical nature of the separated flow at a>0. Even higher (42% of freestream dynamic pressure) pressure fluctuations were observed on the windward side of the nose cap at supersonic speeds and a>7 deg. This is the result of an intermittent shock-shock interaction. The method of Coe et al. of normalizing the spectral data with the local separated flow height was moderately successful in collapsing the data into a manageable number of characteristic spectra. However, the spectra for the spike-induced separation at supersonic speeds agreed better with the results of Speaker and Ailman for two-dimensional step-induced separation than they did with the threedimensional ramp-induced separation of Coe et al. Spectral peaks were observed which corresponded to Roberts' critical subsonic wake flapping frequency.

Matched pressure properties of low altitude plumes

Abstract: Nomenclature A parameter given by Eq. (6a) B = parameter given by Eq. (6b) C = parameter given by Eq. (6c) CD = drag coefficient CF = thrust coefficient D = plume drag F = missile thrust h = enthalpy M = Mach number P = static pressure q = dynamic pressure R = gas constant r = plume radius AS = entropy change T = plume temperature v = plume velocity 7 = ratio of specific heats e = expansion ratio p = plume density £ = parameter given by Eq. (5) or (9)

Interferometric techniques for fundamental static or dynamic pressure measurements and transducer calibration

Abstract: New techniques for the interferometric measurement of quasi-static and dynamic pressure variations are discussed. The pressure variations are transmitted through oil contained in a closed cavity and the measurements depend on an experimental calibration constant derived solely from measurements of mass and length. The sensitivities of the interferometers (a Michelson and a Jamin) are adjusted so that pressure variations produce phase changes of less than +or- pi /2; this then allows the pressure variations to be directly displayed. In an application of the technique pressure transducers are calibrated by mounting the elements in the side of the cavity. Their outputs are then compared with pressure variations measured over the frequency range from 0 (quasi-static pressure changes) to 6 kHz.

A simple total energy sensor

Abstract: This research concerns a simple technique for total energy compensation having the primary requirement of good compensation with a low cost, easy to make sensor. A comprehensive library search and a small wind tunnel were used to explore fundamentals and to develop a number of probes which were flight tested with satisfactory results. Simple probe configurations were tested using the characteristics of laminar flow separation around a small cylinder to produce a sensor pressure having the desired relationship between static and dynamic pressures. Wind tunnel and flight tests confirmed the concepts for a wide range of speeds, altitudes, and flow directions encountered in soaring. Data and findings are presented, along with a discussion of factors important to total energy compensation.

Theoretical Aerodynamics of Over-Wing-Blowing Configuration

Abstract: Previous investigations on OWB aerodynamics2'3 have been centered on the jet entrainment effect, without properly accounting for the dynamic pressure difference in the flowfield because of the presence of the jet. The predicted lift has been found to be too low as compared with experiments, in particular, when the jet is close to the wing. In this paper, the additional lift induced by the over-wing-blowing jets is attributed to the inviscid jet-wing interaction due to the higher jet dynamic pressure and the jet flap effect. The methods used in computing the jet entrainment effect and the wing-jet interaction are summarized in the following. Existing methods for computing jet entrainment are mainly for incompressible, nonheated jets.4 To extend the methods to compressible heated jets, Kleinstein's theory for free compressible jets is revised to include the effect of external stream, with the simplicity of his theory being retained. In this extended theory, the axial velocity is given by

Free-Rocket Trajectory Errors from Plume-Induced Loading during Tube Launch

Abstract: Aerodynamic loads induced on the body of a free rocket during launch from a tube have been investigated by using a cold-gas (N2) static test facility. The rocket had four wrap-around fins, forward bore riders, aft spin rail guides, and a seven-orifice nozzle configuration. Circumferential pressure measurements at various body stations were used to obtain resultant differential pressure distributions. Body pressures were affected by chamber pressure (thrust), gravity drop, longitudinal position of the rocket in the tube, and nozzle orientation. The differential pressure distributions were incorporated into a six-degree-of-freedom computer simulation to estimate the error contribution, using the error budget technique. The plume-induced loading on the rocket afterbody was shown to be a significant source of trajectory error.

Measurement of gasdynamic pressure on a target subjected to CO2 laser radiation

Abstract: Measurements were made of the pressure on the surface of a target subjected to high-power CO2 laser radiation under conditions ensuring one-dimensional motion of the resultant plasma. These measurements were carried out on lead, aluminum, and titanium targets using laser radiation of 107?109?W/cm2 power density. The pressure in the air surrounding the target was varied from 0.07 to 760?Torr. It was found that the pressure on the target surface in vacuum was due to the evaporation of the target material but in air this pressure was governed by the gasdynamics of a laser-absorption wave traveling from the target to meet the incident radiation. The transition from one interaction regime to the other occurred when the air pressure was ~80?Torr.

Measurement of post-separated flowfields on airfoils

Abstract: Detailed experimental measurements have been made of separated flow fields on a two-dimensional airfoil at low speeds. A rather small pitch yaw pressure probe was chosen. This probe has the capability of remote traversing in the vertical axis and remote yawing of plus or minus 180 deg. The calibration of the probe indicates a useful pitch angle range of about plus or minus 45 deg. The probe and its calibrations provide static and total pressure information as well as three components of velocity. Description and calibration of the probe and typical velocity and pressure plots of the separated flow fields are included.

Pitot tube type anemometer - measures wind velocity and direction using differential pressure transducer and rotary potentiometer

Abstract: The anemometer provides an indication of both wind speed and horizontal direction. Wind speed is measured using the Pitot tube principle and provides greater accuracy than impeller type instruments. The rotating head of the anemometer consists of a cylindrical tube (1) with rounded leading edge (2) and outer, coaxial funnel (12), the flared, trailing edge acting as a wind vane (9). The inner tube has an aperture (4) in its leading edge and a second aperture (5) at a point nearer the centre of the head. These apertures are connected to a differential pressure transducer (3) mounted within the head. The dynamic pressure thus measured is proportional to the wind velocity. The electrical signals are conveyed down the mast (11) to a rotary pick-up. Directional data is provided by a rotary potentiometer.

Wall interference effects of static pressure probes in an incompressible turbulent boundary layer

Abstract: Measurements of static pressure across the boundary layer on the wall of a circular cylinder with flow parallel to its axis display wall-interference effects which exceed corrections due to turbulence by almost an order of magnitude. Two different types of static pressure probe were investigated and gave different pressure distributions in the same boundary layer.

Cryogenic wind-tunnel technology

Abstract: The cryogenic concept and the advantages it offers with respect to achieving full scale Reynolds number in a moderate size tunnel at reasonable levels of dynamic pressure are described. Aspects which must be considered during the development of a facility that uses gaseous nitrogen as the test gas are examined. These include the properties of nitrogen, particularly at high pressure; isentropic expansion and normal shock flows in nitrogen; real gas ratios; and the problem of condensation. Sources of information on cryogenic technology are cited.

Research on Wave Phenomena in Hydraulic Lines : 3rd Report, Frequency Characteristics between Pressure and Flow Rate

Abstract: The impedance properties of a wave transmission line containing viscous liquid are experimentally investigated. The pulsating flow rate is measured with an accelerometer connected to a light piston placed at the inlet of a pipe with a closed end. There is good agreement between the experimental results and the theoretical ones given by the axisymmetrical viscous wave equations. Another wave equations considering also a radial pressure gradient are introduced to explain the transition of velocity profile in front of the piston. As the result it is thought the the influence of the piston interposed in oil column decreases rapidly with an increasing distance from it, and is negligible for the present purpose. According to the equations proposed here, dynamic pressure and flow rate in a circular liquid pipe are expressed in infinite series with respect to eigenvalues. A numerical procedure to obtain the eigenvalues for oscillation is developed, too.

Combustion unit in gas turbine

Abstract: PURPOSE:To provide a combustion unit whose swirler is also able to feed the set quantity of air from the source of high static pressure head made available by installing in the air duct the vanes which transform the dynamic pressure head carried in the compressed air into a static pressure head

The characteristics of pitot and static tubes in incompressible flow

Abstract: This chapter discusses the characteristics of the pitot and static tubes for measurement of incompressible flow. In incompressible flow, the velocity pressure can be obtained from the difference between two pressure observations: the total pressure and the static pressure. The measurement of total pressure is relatively simple. On the surface of any solid body immersed in a stream of fluid, there is some point at which the fluid is brought to rest and the pressure acting is the total pressure of the undisturbed flow. This pressure can be determined by providing an orifice at that point and connecting it to a manometer. This is the basis of the pitot tube, which has been universally adopted for the measurement of total pressure. Pitot-static tubes are the only practical standards of reference for the measurement of air speed against which all other designs, and indeed all anemometers, have to be calibrated either directly or indirectly.

Investigation of real-gas and viscous effects on the aerodynamic characteristics of a 40 deg half-cone with suggested correlations for the shuttle orbiter

Abstract: Parameters were evaluated that might be used to correlate shuttle orbiter aerodynamic data to be used in extrapolating from wind-tunnel to flight conditions. Preliminary calculations indicate that the lee-side forces will have an insignificant influence on the aerodynamic characteristics of the orbiter for moderate angle-of-attack entries; therefore, this work is focused on phenomena which have an overriding influence on windward forces, namely, real-gas (equilibrium and nonequilibrium) and viscous-interaction effects. Analytically determined flow fields previously obtained on 40 deg blunted cones were used as a data source to evaluate various correlation parameters. Inviscid effects were found to be the dominant contributor to the aerodynamic coefficients in the altitude range of 64 to 76.2 km. The most suitable correlation of the aerodynamic forces on these cones is based on local dynamic pressure and local Mach number.

Pressure Recovery in a Diffuser for Gas Centrifuge

Abstract: The pressure recovery of supersonic flow at very low density was studied in a vane-island type diffuser for gas centrifuge. A tester of diffuser with a rapidly rotating cylinder was used in experiments. Wall static pressures were measured at many points in the diffuser to observe the static pressure distribution. The change of pressure distribution with back pressure and the effect of flow rate were investigated. Pressure distribution showed that the pressure recovery occurred in the converging section. The pressure ratio increased linearly with the back pressure in this experimental range and the effect of flow rate was not observed. A numerical analysis of the pressure recovery in the channel section of the diffuser was made by applying the finite difference method to the slender-channel equations. The pressure distribution obtained in experiments could be explained as a result of supersonic compression with reverse flow.

Grooving exposure method for spherical dynamic pressure bearing

Abstract: PURPOSE:To botain a spherical dynamic pressure bearing with good performance the medium suction phenomenon of spherical dynamic pressure bearing at high-speed rotating time by engraving a spiral grave to the equator position and to prevent accidents at printing time.

Miscellaneous methods of flow measurement

Abstract: This chapter presents different methods and instruments for the measurement of flow—such as single-observation method, ultrasonic-beam deflexion method, soap-film method, method to study vortex frequency, and laser Doppler anemometer. When the distributions of velocity and static pressure at the section of measurement are fairly symmetrical and conditions there are reasonably steady, a rapid and simple method of determining the mean rate of flow is to establish, by a preliminary exploration, the relation between the mean and the axial velocity and to take single readings of the velocity pressure at the axis of the pipe. The method may be used for large as well as for small pipes, provided that a favorable velocity distribution exists. The soap-film method is used for measurement of very small rates of flow. In this method, the gas or air whose flow is to be measured is passed upward through a vertical glass tube. The laser Doppler anemometer is based on principle of Doppler effect.

Instrument measures dynamic pressure fluctuations

Abstract: Pressure probe instrument, incorporating "infinite line" principle, can be used to remotely measure dynamic pressure fluctuations in hot high-pressure environemnts too severe for sensors. System is designed and can be utilized for measurements in core of operating turbofan engine.

Boundary Layer in a Plasma Blanketed by a Low Pressure Neutral Gas

Abstract: The steady state pressure balance and the diffusions in the boundary layer of a gas-blanketed plasma for the case that a magnetic pressure is much higher than a neutral gas pressure are calculated ...