Showing papers on "Dynamic pressure published in 1980"

Threshold windspeeds for sand on Mars: Wind tunnel simulations

Abstract: Wind friction threshold speeds for particle movement were determined in a wind tunnel operating at martian surface pressure with a 95 percent CO2 and 5 percent air atmosphere. The relationship between friction speed and free-stream velocity is extended to the critical case for Mars of momentum thickness Reynolds numbers between 425 and 2000. It is determined that the dynamic pressure required to initiate saltation is nearly constant for pressures between 1 bar and 4 mb for atmospheres of both air and CO2.

Application of two design methods for active flutter suppression and wind-tunnel test results

Abstract: The synthesis, implementation, and wind tunnel test of two flutter suppression control laws for an aeroelastic model equipped with a trailing edge control surface are presented. One control law is based on the aerodynamic energy method, and the other is based on results of optimal control theory. Analytical methods used to design the control laws and evaluate their performance are described. At Mach 0.6, 0.8, and 0.9, increases in flutter dynamic pressure were obtained but the full 44 percent increase was not achieved. However at Mach 0.95, the 44 percent increase was achieved with both control laws. Experimental results indicate that the performance of the systems is not so effective as that predicted by analysis, and that wind tunnel turbulence plays an important role in both control law synthesis and demonstration of system performance.

Transonic Unsteady Airloads on an Energy Efficient Transport Wing with Oscillating Control Surfaces

Abstract: An aspect ratio 10.8 supercritical wing with oscillating control surfaces is described. The wing is instrumental with 252 static orifices and 164 in situ dynamic pressure transducers for studying the effects of control surface deflection on steady and unsteady pressures at transonic speeds. Results from initial wind tunnel tests conducted in the Langley Transonic Dynamics Tunnel are discussed. Unsteady pressure results are presented for two trailing edge control surfaces oscillating separately at the design Mach number of 0.78. Some experimental results are compared with analytical results obtained by using linear lifting surface theory.

Zero extension line theory of dynamic passive pressure

Abstract: A theory for dynamic passive pressure for sand is developed. The theory is based on a simplified zero extension line field. Equations and charts for computing the dynamic coefficient of earth pressure for various values of wall roughness are presented. The theory is capable of predicting an engineering solution to dynamic passive pressures for the cases of translation, rotation about the top, rotation about the bottom into loose or dense sand. The results are in agreement but generally higher than those predicted by the rigorous methods of associated fields.

Radiation pressure on randomly oriented infinite cylinders.

Abstract: Expressions are developed for the radiation pressure on infinite dielectric cylinders caused by an oblique incidence as a function of the size parameter alpha = 2pialpha/lambda. It is shown that for nonabsorbing cylinders the radiation pressure is always perpendicular to the axis of the cylinder and thus not along the direction of the incident radiation except for the case of normal incidence. This result applies also for other small nonspherical particles. Consequently, the radiation pressure on a randomly oriented nonspinning group of small nonspherical particles causes the particles to spread away from the direction of propagation of the incident radiation. It is suggested that this conclusion should be taken into account when discussing the effect of the radiation pressure on small particles in space, as compared with other forces such as the dynamic pressure on the solar wind.

VTOL in-ground effect flows for closely spaced jets

Abstract: Results of a series of in ground effect twin jet tests are presented along with flow models for closely spaced jets to help predict pressure and upwash forces on simulated aircraft surfaces. The isolated twin jet tests revealed unstable fountains over a range of spacings and jet heights, regions of below ambient pressure on the ground, and negative pressure differential in the upwash flow field. A separate computer code was developed for vertically oriented, incompressible jets. This model more accurately reflects fountain behavior without fully formed wall jets, and adequately predicts ground isobars, upwash dynamic pressure decay, and fountain lift force variation with height above ground.

Air Pressure Measurement Techniques

Abstract: Air pressure is defined as the force acting normal to a unit area. Its SI unit is the Pascal, or Newton m-2 *. In the fluid momentum equations fluid velocities are linked with pressure gradients. The effect of pressure is to transport energy and to redistribute the velocity components towards isotropy, since its effects are independent of direction.

Response to Dynamic Surface Pressure Distributions

Abstract: This paper uses Biot's theory for poroelastic media to examine the response to dynamic surface pressure distribution of layered systems of fluid-filled soils or porous rock. Pressure distributions that are spacially fixed but varying harmonically with time as well as uniformly moving distributions are considered. A general solution is obtained using a Fourier integral transform technique, which is applied to a system consisting of a layer of sand over a base of porous sandstone. Calculated results for deformations, stresses filtering velocities, and fluid flow rates within the layer are presented.

Protection device for innroom abnormal negative pressure

Abstract: PURPOSE:To simplify an air conditioning equipment and to keep the negative pressure inside a room within a fixed range by fitting auto-operative movable vanes in an air feed duct system. CONSTITUTION:When the pressure inside a ventilation room 1 has decreased below a predetermined negative pressure, the dynamic pressure inside an air feed duct 5 decreases, and the decrease in the dynamic pressure is transmitted through a dynamic-pressure introduction duct 23 and a dynamic-pressure blow-off port 24 to movable vanes 22, which are opened by high atmospheric pressure. The outside air is introduced through an outside-air introduction duct 21 into the air feed duct 5, to return the pressure inside the room 1 to a predetermined nagetive pressure. Because the vanes 22 are opened and closed by the balance between the dynamic pressure inside the duct 5 and the atmospheric pressure, the air conditioning equipment is simplified and the negative pressure inside the room is kept constant.

Minimum Energy Test Direction Design in the Control of Cryogenic Wind Tunnels

Abstract: The advent of the cryogenic wind tunnel concept is attributable to the need for high Reynolds number flow in wind tunnels. The cryogenic wind tunnel concept consists of operating the test medium of a conventional tunnel at cryogenic temperatures down to 80 K. Nitrogen gas, cooled by injected liquid nitrogen, proves to be ideal for the cryogenic tunnel test medium because of its near perfect behavior in insentropic flow. Cryogenic operation of a wind tunnel results in reduced fan power consumption and no penalty in flow dynamic pressure. In a cryogenic tunnel, the flow parameters (Reynolds number, Mach number and flow dynamic pressure) can be independently controlled by separately controlling the tunnel flow variables: total temperature, test section mass flow, and the tunnel total pressure. The problem of closed-loop control of the tunnel total temperature, flow Mach number, and total pressure is addressed and reported.

Time-Variant Aerodynamics for Translational Motion of Large-Turning Airfoils.

Abstract: : A cascade of five airfoil sections modelling the hub section of an advanced design turbine featuring a high inlet Mach number and 112 degrees of turning was evaluated at 4 steady-state conditions of varying exit Mach number and expansion ratio The resulting steady-state airfoil surface pressures were compared to a state-of-the-art analytical prediction A time-variant investigation was conducted at the 4 operating conditions of the steady-state experiment Time-variant pressure signals were obtained from a Kulite-instrumented airfoil as the cascade was torsionally oscillated at four values of interblade phase angle per expansion ratio by computer-controlled electromagnetic drive systems The dynamic pressure signals were evaluated in amplitude and phase lag (referenced to blade motion) and correlated with a state-of-the-art analytical prediction based on a flat-plate cascade A quasistatic experiment was performed to relate the dynamic surface pressure amplitudes to those obtained by resetting the cascade to various temporal positions in the torsional cycle of oscillation (Author)

Recording and reproducing device for information signal

Abstract: PURPOSE:To prolong life by leassening the abrasion of a body of revolution by forming a spiral grooves at fixed intervals in the circumferential direction while keeping a slight gap between the body of revolution and a stable plate corresponding to the reverse surface of the body of revolution. CONSTITUTION:Through the turning of body 1 of revolution, air staying in slight gap 3 has negative dynamic pressure by centrifugal force and position dynamic pressure through the viscous pump effect of spiral groove 12. The negative dynamic pressure can be made less than or equal to the positive dynamic pressure by selecting the number of spiral grooves 12, the formation angle of them and the depth of them, and at land part 13, both pressures are equal. According to pressure distribution in slight gap 3, body 1 of revolution, therefore, has pressure equal to circumferential pressure at the outermost circumference and greater than it at its internal circumference and the greatest pressure at the land part of the innermost circumference. Thus, body 1 of revolution can be prevented from deforming by pressure generated in slight gap 3 and the deformation state of body 1 can be determined as you desire.

The Effects of Solidity, Interblade Phase Angle and Reduced Frequency on the Time-Variant Aerodynamic Response of a Compressor Stator.

Abstract: : An experimental investigation was conducted to provide basic unsteady pressure distributions on a stationary vane row, with the primary source of excitation being the wakes generated from an upstream rotor. This was accomplished over a wide range of key parameters in a large-scale, low-speed, single stage compressor. The excitation, the velocity defect created by the rotor blade wakes, was measured with a crossed hot wire. The resulting time-variant aerodynamic response was measured by means of flush mounted high response pressure transducers mounted on a stator vane over a wide range in incidence angles. The dynamic data were analyzed to determine the chordwise distribution of the dimensionless dynamic pressure coefficient and aerodynamic phase lag as referenced to the transverse gust at the vane leading edge. (Author)

The Perfecting of a Harmonic Pick-up for the Simultaneous Detection of the Thickness and Extent of a Fracture Crossed by a Boring

Abstract: The survey of fractured media by non-steady water tests requires the creation of dynamic signals at the entry to the fractures. Apparatus designed for such field survey is described. This apparatus can create a sinusoidal pulse flow inside the fracture and measure the pressure. Between two packers, set above and below the fracture, an alternating piston applies pressure through a membrane to fluid in the fracture. A sensitive oil pressure detector measures pressure and temperature. Signals are transmitted to the head of the boring by a frequency modulation device.

Exhaust gas recirculating device for engine

Abstract: PURPOSE:To improve the operationability of an engine, by controlling an EGR rate in accordance with a loading condition when the engine is in operation CONSTITUTION:When an engine is operated in a specific condition (at its cold state or low speed with a large amount of load and high speed with a small amount of load), a controller 29 inducts a static pressure of a line pressure P between an orifice 8 in an EGR line 7 and an EGR control valve 9 as a power actuating source into a pressure chamber 20 of a negative pressure regulator 18 through lines 24, 26 In this way, pressure in the pressure chamber 20 is relatively lowered to push down a diaphragm 19 by a spring 23 and dilute a negative pressure to a negative pressure chamber 13 While at the time of normal operation of the engine other than the above described specific condition, a dynamic pressure of the line pressure P is inducted as the actuating power source into the pressure chamber 20 through lines 25, 26 to decrease the level of dilution of the negative pressure to the negative pressure chamber 13 and enlarge the opening degree of a valve unit 12 of the EGR control valve 9

Fluid forwarding apparatus by mean of centrifugal vane wheel

Abstract: PURPOSE:To permit fluid blowoff over a wide range by forming a fluid passage through the arrangement of a centrifugal vane wheel between two side plates and forming a suction port at least on one side plate and forming a blowoff port over the whole periphery between two side plates. CONSTITUTION:Air flows into from the fluid suction port 6 of a side plate 2 and passes through a centrifugal vane wheel 1 from the fluid suction port 5 of the centrifugal vane wheel and flows into an annular diffuser 4 and flows out outside, passing through the passage between a static vane 7. The static pressure and the dynamic pressure increase when air passes through the centrifugal vane wheel 1. When passing through the annular diffuser 4, air decelerates, having the direction of stream line gradually getting near the radial direction of the centrifugal vane wheel due to the variation of distance E between the side plates 2 and 3, and a part of the dynamic pressure is converted to the static pressure. The direction of stream line is further varied by the static vane 7, and air is decelerated further, and a portion of the dynamic pressure is converted to the static pressure.