Showing papers on "Dynamic pressure published in 1999"

The Wave-Driven Ocean Circulation

Abstract: Oceanic surface gravity waves have a mean Lagrangian motion, the Stokes drift. The dynamics of winddriven, basin-scale oceanic currents in the presence of Stokes drift are modified by the addition of so-called vortex forces and wave-induced material advection, as well by wave-averaged effects in the surface boundary conditions for the dynamic pressure, sea level, and vertical velocity. Some theoretical analyses previously have been made for the gravity wave influences on boundary-layer motions, including the Ekman currents. The present paper extends this theory to the basin-scale, depth-integrated circulation in a bounded domain. It is shown that the Sverdrup circulation relation, with the meridional transport proportional to the curl of the surface wind stress, applies to Lagrangian transport, while the associated Eulerian transport is shown to have a component opposite to the Stokes-drift transport. A wave-induced correction to the relation between sea level and surface dynamic pressure is also derived. Preliminary assessments are made of the relative importance of these influences using a global wind climatology and an empirical relationship between the wind and wave fields. Recommendations are made for further development and testing of this theory and for its inclusion in general circulation models.

Fault-Tolerant Neural Network Algorithm for Flush Air Data Sensing

Abstract: A fault-tolerant neural network algorithm was successfully developed for use with flush air data sensing systems. This algorithm is composed of a combination of aerodynamic and neural network models used to translate a discrete pressure distribution from the nose of an aircraft into a set of air data parameters, including static pressure, dynamic pressure, Mach number, angle of attack, and angle of sideslip. Techniques were developed to detect and eliminate the effect of a lost signal from the measured pressure distribution. This system was evaluated with archived data, and its performance was compared with a signal processing system based completely on aerodynamic models

Substorm-associated pressure variations in the magnetotail plasma sheet and lobe

Abstract: Simultaneous pressure measurements by Interball-Tail in the high-latitude lobe and by Geotail in the equatorial plasma sheet were analyzed for 30 substorms which exhibited significant pressure changes. At the onset of a few substorms we observed equatorial pressure peaks with magnitudes up to 50% higher than those in the lobe. These pileups are probably rather localized, and their properties are consistent with plasma sheet thickening between two active regions in the tail. During expansion and recovery phases of more than half of substorms, we observed equatorial pressure depletions relative to the high-latitude lobe pressure. These depletions can last more than 2 hours and are likely formed during the substorm expansion phase near the equatorial plane behind (tailward of) the strongly dipolar near-Earth magnetotail region. The observed pressure gradient is probably a nonstationary feature and can be compensated partially by magnetic tension on the curved field lines. Magnitude and history of the solar wind dynamic pressure appear to significantly influence substorm scenarios in the magnetotail. Possible existence of the pressure difference should be taken into account in single-spacecraft substorm studies.

A Numerical Study of Traveling Microbursts

Abstract: An analysis of traveling microbursts in unidirectionally sheared environments is undertaken using a three-dimensional numerical model with 50-m resolution in a 19 × 12 × 4 km domain. For each run, the cooling source is centered at a height of 2 km and travels in an eastward direction of Cm, where Cm = 3, 6, 9, 12, and 15 m s−1. Environmental winds above 2 km are equal to Cm and decay linearly to 0 m s−1 below 2 km. The authors examine the kinetic energy budget of each run, focusing on the dynamic features that are not found in a static microburst simulation. As the source speed Cm increases from 0 to 9 m s−1, the magnitude of the surface horizontal winds increase in the direction of source movement. An examination of the dynamic pressure equation shows that rotationally induced pressure work forces are primarily responsible for increasing surface horizontal winds for the moving-source microbursts. In a similar form to previous studies of vertical perturbations in a sheared environment, elevated h...

Integrated spark plug ignition coil with pressure sensor for an internal combustion engine

Abstract: An ignition coil, spark plug, and pressure sensor for an internal combustion engine are integrated into a single assembly and mounted directly on a plug hole of an internal combustion engine. A hard spark plug shell serves as a magnetostrictive section for pressure detection. A radially polarized biasing magnet is disposed adjacent the spark plug shell thereby generating an initial flux through a sensing winding. The sensing winding is wound about the lower end of the coil case to sense changes in the induction characteristics of the spark plug shell as a result of pressure changes in the cylinder. A first passive method of sensing pressure whereby the flux change due to the permeability change generates a signal voltage in the sensed coil. This voltage is proportional to the time rate of change of pressure which is integrated to produce a cylinder pressure waveform. A second active method employs an oscillator to drive the sensing circuit with a frequency at least ten times that of the pressure signal content. The frequency or amplitude of this signal is then modulated in response to the induction property change of the spark plug shell the induction changes The second method is capable of detecting both static and dynamic pressure.

Gain-Scheduled Linear Fractional Control for Active Flutter Suppression

Abstract: A gain-scheduled controller for active e utter suppression of the NASA Langley Research Center’ s Benchmark Active ControlsTechnology wing section is presented. Thewing section changessignie cantly as a function of Mach and dynamicpressureand ismodeled asa linearsystem whoseparameters depend in a linearfractionalmanneron Mach and dynamic pressure. The resulting gain-scheduled controller also depends in a linear fractional manner on Mach and dynamic pressure. Stability of the closed-loop system over a wide range of Mach and dynamic pressure is demonstrated. Closed-loop stability is demonstrated via time simulations in which both Mach and dynamic pressure are allowed to vary in the presence of input disturbances. The linear fractional gain-scheduled controller and an optimized linear controller (designed for comparison ) both achieve closed-loop stability, but the gain-scheduled controller outperforms the linear controller throughout the operating region.

Apparatus for altering the physical properties of fluids

Abstract: A system for fluid processing is provided to control shear, point velocity and pressure in either a Newtonian or non-Newtonian fluid which includes creation of three fields, namely a dynamic microshear field, a dynamic velocity field and a dynamic pressure field, with the fields being created by the injection of energy between 1 KHz and 10 MHz into the fluid. Control is achieved by control of the angle at which mechanical energy is delivered, steering and/or focusing of the energy, control of the amplitude of the energy waveform, of the energy, and control of the frequency of the energy in one embodiment to eliminate standing waves. By controlling the three fields, the system is able to control overall fluid behavior. In one embodiment, energy is injected into a fluid at any angle to the direction of flow assuming the fluid is flowing, with the injected energy providing a predetermined controllable zone of energy in the fluid at the region of energy injection. In another embodiment, the container itself is a transducer that acts as a processor, where the energy comes from the container itself. In a further embodiment, a phased array is used for electronically steering and focusing energy to any point within the fluid volume to provide for the desired shear, velocity and pressure distributions. Note that the direction and focusing of the injection of energy is turnable by physically moving a transducer or by the use of a phased array.

Magnetic Energy Release in Flux Pile-up Merging

Abstract: The problem of pressure limitations on the rate of flux pile-up magnetic reconnection is studied. We first examine the recent suggestion of Jardine and Allen (1998) for moderating the build-up of magnetic pressure in the current sheet by considering inflows with nonzero vorticity. An analytic argument shows, however, that unbounded magnetic pressures in the limit of small resistivities can be avoided only at the cost of unphysical dynamic pressures in the plasma. Hence, the pressure limitation on the reconnection rate in a low-beta plasma cannot be avoided completely. Nevertheless, we demonstrate that reconnection can be more rapid in a new solution that balances the build-up in dynamic pressure against both the plasma and magnetic pressures. This exact MHD solution has the characteristics of merging driven by the coalescence instability. The maximum energy release rate of the model is capable of explaining a modest solar flare.

Experimental and computational determination of the VKI Plasmatron operating envelope

Abstract: The present paper deals with the experimental determination of the operating envelope of the Plasmatron facility, designed and built at the von K&m&n Institute for Fluid Dynamics as the test bench of the European Space Agency to perform testing of TPS materials before their use in flight. As such the prime requisite of the facility is its capacity to reach specified values of stagnation pressure and catalytic cold wall stagnation point heat flux. These two variables are measured using a water-cooled Pitot probe and a steady-state heat flux probe. The paper contains the description of these probes and details about their use, as well as an analysis of experimental uncertainty. The results of the envelope exploration are presented and it is shown that the facility reaches and outdoes its basic requirements. The experimental results are also compared to the values predicted by a quasi-one-dimensional nozzle code of a plasma flow in chemical equilibrium. It is shown that the experimental values agree well with the predicted values. Results of measurements at various positions of the plasma jet are also reported. The decrease of heat flux and dynamic pressure with axial distance from the torch is essentially linear. The onedimensional model was shown to fail to predict the effect of mass flow rate, due to strong twodimensional effects in the jet. Perspectives of supersonic operation are examined in view of the pumping capacity. A brief description of the facility is also part of the report.

Aerodynamic Torque Acting on a Butterfly Valve. Comparison and Choice of a Torque Coefficient

Abstract: Most technological devices use butterfly valves to check the flow rate and speed through piping. Their main advantages are their low cost, their mechanical suitability for fast operation, and their small pressure drops when they are fully open. The fluid dynamic torque about the axis of large valves has to be considered as the actuator could be overstrained. This torque is generally defined using a nondimensional coefficient K T , in which the static pressure drop created by the valve is used for normalization. When the valve is closed downstream of an elbow, the valve pressure drop is not well defined. Thus, the classic normalization method gives many ambiguities. To avoid the use of the pressure drop, we define another torque coefficient C T in which the dynamic pressure of the flow is the normalization factor instead of the pressure drop. Advantages and drawbacks of each normalization method are described in the following.

An experimental study of vortex generators in boundary layer ingesting diffusers with a centerline offset

Abstract: A fundamental experimental investigation was conducted on the flow characteristics and performance of a diffuser ingesting a thick boundary layer of a high shape factor. The duct is characterized by a S-shaped offset and a cross-sectional area change going from a semi-circle at the entrance to a full circle at the exit. The performance of the diffuser was quantified by the two parameters of primary concern in jet engine applications: Total pressure recovery and total pressure distortion at the fan face (i.e. the exit) calculated from the total pressure data measured inside the duct. Flat plate vortex generators (vg’s) were deployed in an attempt to alter the flow structure inside the diffuser and eliminate separation in order to realize improvements in the diffuser performance descriptors. It was readily observed that the presence of the offset had a very strong effect on the behavior of the flow, causing separation and strong secondary flows in the Sduct accompanied by total pressure recovery of approximately 90% and total pressure distortion at the fan face of 77% (normalized to dynamic pressure) for the base case without flow control. Installation of vg’s in the Sduct helped to decrease the distortion to about 11% in some cases and prevented flow separation. However, in all cases, it was not possible to improve the pressure recovery in the S-duct much beyond the 90% range for the base flow with no vg’s.

A Compensated Acoustic Actuator for Systems with Strong Dynamic Pressure Coupling

Abstract: This study improves the performance of a previously developed acoustic actuator in the presence of an acoustic duct system with strong pressure coupling. The speaker dynamics and the acoustic duct dynamics are first modeled separately. The two sysrems are then coupled, and the resulting system is modeled. A velocity sensor is developed and used in feedback compensation. The resulting speaker system has minimal magnitude and phase variation over a 20-200 Hz bandwidth. These conclusions are verified through experimental results.

Apparatus for Atmospheric Surface Layer Measurements over Waves

Abstract: This paper describes an apparatus developed for simultaneously measuring water elevation and static and dynamic pressure, momentum, and heat fluxes above waves close to the interface. The apparatus was used successfully at the Lake Ontario wave research tower of the Canada Centre for Inland Waters. The principle and purpose of the various sensors used, calibration procedures, and data-gathering processes are described. Simultaneous measurements of the atmospheric surface layer’s physical quantities are presented. All the quantities necessary to close the kinetic energy budget in the atmospheric surface layer have been measured.

Simulation of Flow Around Hypersonic Blunt-Nosed Vehicles for the Calibration of Air Data Systems

Abstract: Control of a hypersonic vehicle in flight requires knowledge of the vehicle state to sufficient accuracy. Particularly important state data are the air data which describe the ambient atmosphere, and its interaction with the moving vehicle. Such information includes vehicle angle of attack, angle of sideslip, and dynamic pressure. Flush air data systems are commonly installed on blunt-nosed hypersonic vehicles to infer air data through consideration of pressure measurements made at the vehicle surface. An accurate pressure model, describing the relationship between air data parameters and surface pressure distribution, is required for such inferences to be made.In this work, a new computational fluid dynamics code is developed for the primary purpose of calibrating surface pressure models for use with flush air data systems. In particular, the hypersonic flight experiment (HYFLEX) vehicle is used as a case study. When tested with flight data, results from the calibrated HYFLEX flush air data system exhibit approximately doubled accuracy in estimating vehicle angle of attack and dynamic pressure, compared to an uncalibrated system. Also, the numerical calibration procedure has accuracy and efficiency advantages, compared to traditional, experiment-based calibrations.The selection and development of algorithms for use in the computational fluid dynamics code are described in detail in the thesis. Particular attention is paid to assessing the suitability of different numerical approaches and models for simulating the flow pressure field around blunt bodies at high speed. A largely original shock fitting formulation is used to improve the accuracy and robustness of the computational fluid dynamics program. The advection upwind splitting method, combining difference and vector splitting, is found to be a good technique for computing fluxes in blunt-body flow simulations. Also, a new modification to the van Albada limiter and monotone upwind scheme for conservation laws is used to provide accurate solution reconstruction. A range of validation and verification test cases are presented, to ensure that simulation results are credible. Some common failings of numerical simulation techniques are investigated, and suppressed or avoided. Such failings include excessive numerical dissipation, shock instability, shock smearing, spurious numerical noise and oscillation, and odd-even decoupling.

Square-wave pressure generator using a novel rotating valve

Abstract: To generate dynamic pressure precisely at low- and medium-pressure levels and in a low-frequency range, we have developed a square-wave pressure generator using a novel rotating valve. The main features of the valve are chambers in the rotor and grooves inside the stator. Pressurized air from two sources is continuously supplied to each chamber through the grooves. The valve switches the pressure alternately by its rotation, producing square-wave pressure. The amplitude and fundamental frequency of the generated pressure can be changed arbitrarily. The measured waveform is a periodic well-shaped square wave. The experimental results show that the repeatability of the system is good for a dynamic pressure source.

Liquid dynamic pressure bearing and the spindle motor

Abstract: PROBLEM TO BE SOLVED: To reduce mutual interference of an axial dynamic pressure part and a radial dynamic pressure part on a ring liquid dynamic pressure bearing. SOLUTION: Ring spaces 8, 9 to reserve lubricating oil for generation of dynamic pressure are provided along a neighbouring part of a radial dynamic pressure bearing part and an axial dynamic pressure bearing part formed between a ring 3 and a bearing part 5 and negative pressure is not generated in a boundary region of both of the dynamic pressure bearing parts in a ring liquid dynamic pressure bearing 1 constituted as a shaft part 4 constituted with the ring 3 fixed on an end part 2A of a shaft main body 2 supported by the bearing part 5. COPYRIGHT: (C)2000,JPO

Hydrodynamic bearing device

Abstract: A hydrodynamic bearing which prevents a lubricating fluid from scattering out of the dynamic pressure generating portion. The bearing includes radial spacing d of a gap at an open end of the thrust-side dynamic pressure generating portion, whose value is greater than a spacing of the thrust-side dynamic pressure generating portion, as measured relative to the thrust direction. Scattering of lubricating fluid from the open end of the thrust-side dynamic pressure generating portion is therefore prevented even when the bearing rotates at a high speed in a high temperature envivronent.

Fluid bearing equipment

Abstract: An object of the present invention is to provide a fluid bearing equipment which is free from lockup or seizure which may occur due to a deficiency of a lubricating fluid when the equipment is operated at a high rotation speed in a high temperature environment. The fluid bearing equipment is arranged such that maximum pressure generating portions 23 of dynamic pressure generating grooves 15, 16 provided in a thrust-side dynamic pressure generating portion are located closer to the outer circumference of a stationary thrust plate 9 than a radially middle position of the thrust-side dynamic pressure generating portion. With this arrangement, the lockup and seizure of a motor can be prevented which may otherwise occur due to a deficiency of the lubricating fluid when the equipment is operated at a high rotation speed in a high temperature environment.

Active flutter suppression via gain-scheduled linear fractional control

Abstract: A gain-scheduled controller for active flutter suppression of the NASA Langley Research Center's Benchmark Active Controls Technology wing section is presented. The wing section changes significantly as a function of Mach and dynamic pressure and is modeled as a linear system whose parameters depend in a linear fractional manner on Mach and dynamic pressure. The resulting gain-scheduled controller also depends in a linear fractional manner on Mach and dynamic pressure. Stability of the closed-loop is demonstrated via time simulations in which both Mach and dynamic pressure are allowed to vary in the presence of input disturbances. The linear fractional gain-scheduled controller and an optimized linear controller (designed for comparison) both achieve closed-loop stability throughout the operating region.

Experimental Investigations of Stall Flutter in a Transonic Cascade

Abstract: The design of modern gas turbines is more and more based on flow simulations by numerical calculation models. Due to the different influence parameters the development and verification of these codes requires detailed data bases, which can only be provided by experimental investigations. The demand of increasing power density leads to higher Mach Numbers up to transonic ranges. Due to the thin blade profiles the risk of stall flutter becomes an extraordinary point of interest. Therefore, in a transonic wind tunnel a cascade of nine compressor blades designed by MTU Munich were investigated at different inlet Mach numbers and incidence angles. To get information about flow behavior at steady state, profile pressure distribution was measured at midspan with pressure taps on profile surface. In order to provide information about the overall flow field oil flow visualization and Schlieren technique were applied for the investigation at steady state. For flutter simulation the blade in the middle position of the cascade was forced to torsional oscillating movement by an electromagnetic shaker system with a frequency of f = 310.0 Hz. The flow behavior with oscillating and fixed center blade was investigated at midspan by means of dynamic pressure transducers and hot films glued on profile probes. The results of these investigations are presented in this paper especially up to the appearance of stall flutter.Copyright © 1999 by ASME

Method and apparatus for altering the physical properties of fluids

Abstract: A system for fluid processing is provided to control shear, point velocity and pressure in either a Newtonian or non-Newtonian fluid, which includes creation of three fields, namely a dynamic microshear field, a dynamic velocity field and a dynamic pressure field, with the fields being created by the injection of energy between 1 KHz and 10 MHz into the fluid. Control is achieved by control of the angle at which mechanical energy is delivered, steering and/or focusing of the energy, control of the amplitude of the energy waveform, of the energy, and control of the frequency of the energy in one embodiment to eliminate standing waves. By controlling the three fields, the system is able to control overall fluid behavior. In one embodiment, energy is injected into a fluid at any angle to the direction of flow assuming the fluid is flowing, with the injected energy providing a predetermined controllable zone of energy in the fluid at the region of energy injection. In another embodiment, the container itself is a transducer that acts as a processor, where the energy comes from the container itself. In a further embodiment, a phased array is used for electronically steering and focusing energy to any point within the fluid volume to provide for the desired shear, velocity and pressure distributions. Note that the direction and focusing of the injection of energy is turnable by physically moving a transducer or by the use of a phased array.

The hoverwing technology-bridge between WIG and ACV

Abstract: Wingships (WIG, Wing In Ground) utilise water as runways to reach their lift-off speed, which is determined by the wing loading. High Wing loadings are desirable for high cruising speeds with inherent height and longitudinal stability. To build up the necessary dynamic air pressure under the wings, they need roughly 3 times more power to overcome the hydrodynamic hump-drag compared to the drag during ground effect flight. So it is necessary to develop suitable devices as lift-off-aids in order to reduce the recommended power. With support of the German Ministry for R&D (BMB+F) Fischer-Flugmechanik (FF) has developed the Hoverwing - Technology in order to further reduce the necessary lift-off power. The principle of this technology, for which FF has patent rights, is the building up of static air pressure between the catamaran float. After lift-off the dynamic pressure will replace the static pressure and the craft operates as a WIG with high lift to drag ratios. FF is developing the Hoverwing 80, with the target to transport 80 passengers at 100 kts. Some test results with a scaled down two Seater will be demonstrated by video extracts

Pressure control system for passenger compartment of vehicle

Abstract: The vehicle has a ventilator which is closed in response to an external pressure wave. A valve (V) connects the compartment to an inlet orifice (O) that is located in an area of high dynamic pressure, and a sensor (P) which measures absolute pressure is located in the compartment. A controller which operates the ventilation is provided. This opens the valve in response to a reduction in pressure being sensed by the sensor and so limits the reduction in internal pressure.

Ales shallow-water flow solver with non-hydrostatic pressure: wave applications

Abstract: A shallow-water flow solver with non-hydrostatic pressure in a coordinates has been developed to include effects due to the moving grid, referred to as the ALES approach. The formulation is outlined for 2D vertical plane problems and tested against experimental data for wave flows over plane beds, bars and trenches. Agreement with experiment is generally good and the importance of non-hydrostatic pressure and moving-grid terms is demonstrated.

Dynamic pressure air bearing

Abstract: PROBLEM TO BE SOLVED: To provide a low-cost bearing of high accuracy by forming the bearing of a sintered alloy, providing a bearing face opposed to the outer peripheral surface of a shaft through a clearance, and inclined dynamic pressure grooves formed on the bearing face, and levitating to support the shaft by dynamic pressure action of air in the clearance. SOLUTION: A bearing face 4 opposed to the outer peripheral surface of a shaft through a bearing clearance is formed on the inner peripheral surface of a bearing body 1 formed of a sintered alloy into porous cylindrical shape. The bearing face 4 has a first dynamic pressure generating area m1 with a plurality of dynamic pressure grooves 5 inclined in one direction in relation to an axial direction and arranged in a circumferential direction, a second dynamic pressure generating area M2 axially separated from the first area M1 and having a plurality of dynamic pressure grooves inclined in the other direction in relation to the axial direction and arranged in the circumferential direction, and an annular smooth part (n) formed between both areas M1, m2. Air is collected to the smooth part (n) by the relative rotation of the shaft and bearing body 1, and dynamic pressure at this part is heightened. Bearing rigidity is increased because of no dynamic pressure groove in the smooth part (m). The grooves 5 can be formed by compression molding so as to reduce cost, and thermal deformation is small because of the sintered alloy so as to be able to maintain high accuracy even under high temperature.

Application of the Subsonic Doublet Lattice Method to Delta Wings

Abstract: cylindricalbagswere not used for dissipatingthe impact energy, but instead were used for combining the two cube bags. Shear pin-type vents were applied to release gas to avoid rebounding at ground impact. The vent area was calculatedwith the method presentedby Idomir.2 Theparametersof the circular-shapedbagweredetermined by the same procedure. A photoelectron-quick-release and cable-suspensionsystemsuitable for an indoor test was used. With this equipment, the verticaland horizontal-velocitycomponentscould be obtained.Accelerometers were glued near the model’s c.g. to measure the vertical and horizontal acceleration. To monitor the dynamic pressure during impact, a pressure sensor was installed in the airbag. Test data were recorded on the oscillometer and processed by a computer. In the case of vertical drops in various initial yaw or/and roll conditions,it is shown that themulticompartmentairbagcan provide better attenuation. A slight tipover occurs only under the poorest test conditions, 19-deg roll and 16-deg yaw. When the horizontal velocitycomponentis in a given range.(<2m/s, limitedby the room size), the payloads drop steadily. The range is related to the width of bag and the height of the payload. Figure 2 shows a photograph of the typical model–airbag system at the end of the drop test. The dynamic properties of the bags are also studied systematically. It is found that several factors affect the impact deceleration. Among these factors, the drop velocity and initial pressurehave signiŽ cant effects on the peak deceleration.Experiments indicate that the retarding force-strokecurve (Fig. 3), is different from the curve presented by Knache.