Showing papers on "Dynamic pressure published in 2007"

Influence of Splitter Blades on the Flow Field of a Centrifugal Pump:Test-Analysis Comparison

Abstract: This work aims at studying the influence of adding splitter blades on the performance of a hydraulic centrifugal pump. The studied machine is an ENSIVAL-MORET MP 250.200.400 pump (diameter = 408 mm, 5 blades, specific speed = 32), whose impeller is designed with and without splitter blades. Velocity and pressure fields are computed using unsteady Reynolds-averaged Navier-Stokes (URANS) approach at different flow rates. The sliding mesh method is used to model the rotor zone motion in order to simulate the impeller-volute casing interaction. The flow morphology analysis shows that, when adding splitter blades to the impeller, the impeller periphery velocities and pressures become more homogeneous. An evaluation of the static pressure values all around the impeller is performed and their integration leads to the radial thrust. Global and local experimental validations are carried out at the rotating speed of 900 rpm, for both the original and the splitter blade impellers. The head is evaluated at various flow rates: 50 % , 80 % , 100 % , and 120 % of the flow rate at the best efficiency point (BEP). The pressure fluctuations are measured at four locations at the BEP using dynamic pressure sensors. The experimental results match the numerical predictions, so that the effect of adding splitter blades on the pump is acknowledged. Adding splitters has a positive effect on the pressure fluctuations which decrease at the canal duct.

Simulation of Losses Due to Turbulence in the Time-Varying Vocal System

Abstract: Flow separation in the vocal system at the outlet of a constriction causes turbulence and a fluid dynamic pressure loss. In articulatory synthesizers, the pressure drop associated with such a loss is usually assumed to be concentrated at one specific position near the constriction and is represented by a lumped nonlinear resistance to the flow. This paper highlights discontinuity problems of this simplified loss treatment when the constriction location changes during dynamic articulation. The discontinuities can manifest as undesirable acoustic artifacts in the synthetic speech signal that need to be avoided for high-quality articulatory synthesis. We present a solution to this problem based on a more realistic distributed consideration of fluid dynamic pressure changes. The proposed method was implemented in an articulatory synthesizer where it proved to prevent any acoustic artifacts

Tire inflation method

Abstract: A method of inflating a tire, or vehicle tire, that minimizes the amount of time needed for same is disclosed. The method of inflating a tire with a tire pressure management system includes introducing continuous fluid flow of a fluid into the tire, ascertaining the dynamic pressure of the fluid during said introducing continuous fluid flow, terminating continuous fluid flow when the dynamic pressure exceeds or equals a predetermined amount, and introducing pulsed fluid flow of the fluid into the tire.

Wind turbine blade tip comparison using CFD

Abstract: The effect of wind turbine blade tip geometry is numerically analysed using Computational Fluid Dynamics (CFD). Three different rotating blade tips are compared for attached flow conditions and the flow physics around the geometries are analysed. To this end, the pressure coefficient (Cp) is defined based on the stagnation pressure rather than on the inflow dynamic pressure. The tip geometry locally modifies the angles of attack (AOA) and the inflow dynamic pressure at each of the studied sections. However not all 3D effects could be reduced to a change of these two variables. An increase in loadings (particularly the normal force) towards the tip seem to be associated to a spanwise flow component present for the swept-back analysed tip. Integrated loads are ranked to asses wind turbine tip overall performance. It results from the comparison that a better tip shape that produced better torque to thrust ratios in both forces and moments is a geometry that has the end tip at the pitch axis. The work here presented shows that CFD may prove to be useful to complement 2D based methods on the design of new wind turbine blade tips.

Measurement of ski snow-pressure profiles

Abstract: Bulge-disc type pressure sensors of diameter 6 mm were fitted as near as possible to the running edge of a modern carved ski. The pressure signals were sampled at 30 Hz during long turns on snow, synchronously with signals from a geomagnetic compass and a pressure pad in the ski boot. The pressure from the snow was found to be highly variable with a mean value of about 50 kPa and dynamic pressure spikes up to 300 kPa. With the outside leg, the snow contact width in the rear part of the ski was found to be slightly wider, on average, than for the front part, as expected for a carving turn. Correlation within the pressure sensor data showed that the rapid pressure fluctuations were probably not due to bumps or features on the snow; instead they were probably caused by many small-scale collapses of the snow structure as the ski passed.

``Compression aurora'': Particle precipitation driven by long-duration high solar wind ram pressure

Abstract: [1] The transient behavior of shock-induced auroras reported by previous workers suggests a cause-and-effect relationship between the shock front and the auroral transient. However, it is not known if the high solar wind dynamic pressure downstream of a shock can have significant effects on the global auroral morphology. In this brief report we present results from an observational study on global auroral response to large solar wind dynamic pressure, using global auroral images acquired by the ultraviolet imager on board the Polar spacecraft. It is found that the luminosity of the aurora showed a general prompt and lasting increase in the dawn and dusk flanks of the oval. Such an auroral activity is closely related to the compression of the magnetosphere and is thus christened “compression aurora.” The luminosity increase, though predominantly in the dawn sector of the oval, may persist as long as the solar wind dynamic pressure stays high and may disappear ∼10 min after the dynamic pressure drops. A detailed examination of Defense Meteorological Satellite Program particle data on one fortuitous event on 26 September 1999 indicates that the compression aurora is produced mainly by precipitating electrons originating from the central plasma sheet (CPS). Plasma wave observations made from Geotail in the dawn sector of the near-Earth plasma sheet indicates no expected plasma wave activity that may have been otherwise considered a primary cause of enhanced CPS particle precipitation through a pitch angle loss by wave-particle interactions. We propose that reductions of the Earth's magnetic field mirror ratio by magnetospheric compression can be a prime mechanism for the compression aurora as long as there is a continuing supply of particle source.

Magnetic activity in the polar caps: Relation to sudden changes in the solar wind dynamic pressure

Abstract: [1] Response of the polar cap (PC) magnetic activity to sudden changes in solar wind dynamic pressure is analyzed with use of the northern and southern polar cap indices for 1998–2002 and corresponding solar wind parameters: geoeffective interplanetary electric field (Em) and the solar wind dynamic pressure (PSW), reduced to the magnetopause Only sudden pressure pulses starting against the background of steady quiet pressure levels were taken for the analysis To separate effects produced by Em and PSW, we examined the behavior of the average characteristics PSW, Em, and PC under the different restrictions imposed in turn on (1) electric field Em, (2) magnitude of the pressure PSW after the jump, and (3) rate of the pressure increase (dPSW/dt), the other two quantities being kept invariant in so doing The following results have been obtained The electric field Em determines behavior of the PC index, the value of which is directly influenced by the Em increase with a delay time of about 15–30 min The solar wind pressure growth rate (ie, jump power dPSW/dt) appears to be the second most important factor for the PC index increase, the pressure gradient dPSW = 1 nPa being approximately equivalent to the action of dEm = 033 mV/m, with a delay time shortened up to a few minutes The growth rate of the pressure gradient seems to be the sole factor for the PC index increase under conditions of the northward interplanetary magnetic field BZ and for the PC index decrease after the dynamic pressure negative jump

Hypersonic Missile Performance and Sensitivity Analysis

Abstract: The performance of a conceptual, missile-class, hypersonic vehicle was modeled using a 2-degree-of-freedom dynamics model. The vehicle was assumed to be air launched, accelerated to a Mach number of 3 using a solid propellant rocket, and subsequently propelled using a dual-mode scramjet engine to cruise at Mach numbers between 4 and 9. Modeling results show that fuel storage capacity and dynamic pressure have a significant effect on vehicle range and average speed. A perturbation analysis was also performed that ranked the sensitivity of missile rangetosmallchangesin14designparameters.Thekineticenergyefficiency(totalpressureloss)ofthescramjethas the highest effect on performance at high cruise Mach numbers (6.7–9), followed by structural mass, combustion efficiency, and aerodynamics parameters. At low cruise Mach numbers (4–6.7), structural concerns dominate performance, followed by the aerodynamics and scramjet operating parameters.

On Characteristics of Velocity and Pressure Field in Two-Dimensional Turbulent Jet

Abstract: Fluctuating static pressure is closely related with fluctuating velocity in a turbulent flow, and it plays an important role in the energy balance and anisotropy of turbulence. Thus, the measurement of the fluctuating static pressure is significantly effective for the clarification of the organized structure of the turbulent flow. In this study, a static probe that is less sensitive to the yaw angle and having a good frequency response was developed, and the simultaneous measurement of velocity and pressure field was performed in a two-dimensional jet flow by a combination of this static pressure probe and an I-type hot-wire probe. In the pressure spectrum, the κ-7/3 power law range could be clearly observed, and the distribution of the cross-correlation between streamwise velocity and static pressure is demonstrated to be consistent with the previous model of coherent vortex structure.

Beam heat load and pressure rise in a cold vacuum chamber

Abstract: The beam heat load and the pressure in the vacuum chamber of the cold bore superconducting undulator installed at ANKA (ANgstrom source KArlsruhe) have been monitored for almost two years. Possible sources of the observed heat load could be synchrotron radiation from upstream magnets, image currents, electron and ion bombardment. In this paper, the various possible contributions to the heat load are discussed and compared with experimental results. The dynamic pressure increases nonlinearly with the average beam current. The current where it assumes a maximum varies both with the bunch intensity and with the initial vacuum pressure. A correlation between the heat load and the dynamic pressure has been observed. This study suggests that electron bombardment could explain the beam heat load and pressure rise observed for a bunch length of 10 mm.

Response of the magnetic field in the geosynchronous orbit to solar wind dynamic pressure pulses

Abstract: [1] We do a statistical survey of solar wind dynamic pressure (Pd) pulses and geosynchronous magnetic fields observed between 1998 and 2005. In geomagnetic quiet times with Dst > −50 nT, we find 111 solar wind dynamic pressure pulses which produce geosynchronous magnetic field responses. These responses are often observed by two or three GOES spacecraft at different local times in geosynchronous orbit. The magnitudes of the geosynchronous magnetic field changes (dBz) have a peak near the noon meridian, similar to the results obtained in the study of the response of the geosynchronous field to the large and sharp solar wind dynamic pressure variations. However, the relative change of the geosynchronous magnetic field dBz/AV-Bz (where AV-Bz is the average of the geosynchronous magnetic field Bz observed during the response to the pressure pulse) depends weakly on the local time; thus the change of Bz(dBz) is proportional to the average field (AV-Bz). As the magnitude of the relative change of solar wind dynamic pressure (dPd/Pd) increases, the rate of geosynchronous magnetic field variation increases correspondingly. These results imply that the magnitude of the geosynchronous magnetic field response could be determined by AV-Bz. In addition, the interplanetary field orientation does not affect the response significantly. Using an MHD code which models the global behavior of the solar wind-magnetosphere-ionosphere system, we reproduce the main characteristics of the observations.

Behavior of Top-Blown Jet under Reduced Pressure

Abstract: In steelmaking, the top-blown oxygen jet is used in many different refining processes and its behavior is therefore an important factor in steel refining. Numerous studies have been conducted on jet behavior under atmospheric pressure conditions; however, its behavior under reduced pressure for vacuum refining processes is still not fully understood.In this study, jet behavior under reduced pressure was investigated by measuring the dynamic pressure of the jet. Also, numerical simulation, which was used for jet simulation in recent studies, was carried out to clarify the details of the jet behavior. The simulated results were compared with the measured data and the numerical simulation method was validated.As a result, the jet behavior was modeled using the numerical simulation, and the detailed effects of ambient pressure on the jet behavior were clarified. The potential core of the jet lengthened as the ambient pressure decreased, indicating that jet attenuation under reduced pressure is smaller than that under atmospheric pressure. Using this model, the effect of the nozzle shape on the post combustion behavior of the actual RH top-blown process could be explained.

Solar wind–magnetosphere coupling efficiency for solar wind pressure impulses

Abstract: [1] We investigate the solar wind–magnetosphere coupling efficiency in response to solar wind dynamic pressure impulses. We carry out a superposed epoch analysis of 236 pressure impulses from the years 1998–2002 detected by the ACE/SWEPAM instrument. For the coupling efficiency, we use four definitions based on: the polar cap potential from SuperDARN radars, the northern polar cap index (PCN), the available magnetospheric potential, and the interplanetary electric field (IEF). All definitions show consistent results: the coupling efficiency depends on the internal structure of the impulse. The coupling efficiency increases (decreases) for events mimicking slow (fast) MHD shocks. The coupling energy estimated from the IMAGE magnetometer chain is larger for the “fast-type” events and stronger drivers. Hence, our results indicate that the magnetosphere uses the energy from the weaker driver more geoeffectively, while the energy associated with stronger drivers is partly transmitted through the system.

Determination of Atmospheric Densities from Reentry Flight Data

Abstract: Twomethods to infer freestream densities from in-flightmeasurements of pitot pressure and flight velocity during reentry are presented that focus on the minimization of uncertainties due to high-temperature real-gas effects and atmospheric densityfluctuation. A numerical approach leads to a curve-fit function that yields the ratio of the pitot to the dynamic pressure pt2=q1 for velocities between 0.5 and 10 km=s and altitudes up to 90 km. An analytically derived correlation is also provided. Both techniques account for equilibrium real-gas effects thus achieving very high accuracies. Independently of potential atmospheric fluctuation, remaining errors are less than 1% for almost the entire spectrum and less than 0.3% for typical lifting reentry.

Navigation system with dynamically calibrated pressure sensor

Abstract: A navigation system includes a pressure sensor, a calibration module in communication with the pressure sensor, and an altitude module in communication with the calibration module. The calibration module is configured to determine a dynamic pressure proportionality coefficient based at least in part on a static pressure proportionality coefficient, a measured pressure value from the pressure sensor, and a velocity value. The altitude module is configured to calculate a sensor-based altitude value based at least in part on the determined dynamic pressure proportionality coefficient.

Dynamic Analysis of Wind Tunnel Data from an Isentropic Relaxed Compression Inlet

Abstract: A family of five axisymmetric external compression inlets was tested at Mach 1.97 in the 1-ft ×1-ft supersonic wind tunnel at the NASA Glenn Research Center. All five inlets shared the same external compression surface; they differed only in subsonic diffuser geometry. The external compression surface used an isentropic relaxed compression design developed by Gulfstream Aerospace Corporation. Steady-state pressure data were recorded on the inlet centerbody, on the cowl, and at two pitot pressure rakes located at the aerodynamic interface plane (AIP). High frequency dynamic pressure data were recorded at one static pressure tap on the inlet centerbody and at a pitot probe on the AIP. Schlieren images were also recorded. This paper analyzes the dynamic pressure data from three of the inlet models.

A Study on Measurement of Flare Slamming of Large Container Vessel (II) - Characteristic Analysis of Measured Slamming Pressure -

Abstract: As a container vessel becomes larger, the bow flare becomes larger. The large bow flare structures are often subjected to dynamic pressure loads due to bow flare slamming occurring in rough seas. The aim of this paper is to investigate the characteristics of bow flare slamming pressure measured in a real voyage through the North Pacific Ocean. The characteristics of impact pressure load caused by slamming is addressed in terms of the pressure pulse-time history which involves rising time, peak pressure, decaying time and type of pressure decay. The values were presented using non-dimensional parameters.

Filtering Depth Measurements in Underwater Vehicles for Improved Seabed Imaging

Abstract: Underwater vehicles are commonly used for detailed seabed mapping. To derive a bathymetric map, the depth of the underwater vehicle must be known. The offshore survey industry has often strong requirements on both absolute and relative accuracy. Depth is usually deduced from a measurement of absolute pressure. Regardless of the quality of the pressure sensor, the pressure measurement is influenced by environmental factors, such as waves, tide, atmospheric pressure and sea water density profile. In the paper we analyze these factors with respect to their behavior and effect on the measured depth. An underwater vehicle equipped with an aided inertial navigation system (AINS) has through its accelerometers and Doppler velocity log redundant information on the movement of the underwater vehicle. Using this information, an AINS is well suited to filter out dynamic pressure sensor noise. Linear wave theory is used to model the effects of the waves on the pressure sensor, and it is suggested how the parameters of the pressure sensor noise model can be deduced from the mean wave amplitude and period. AINS performance is often substantially improved by post-processing. The paper will therefore examine the depths outputted from the pressure sensor, from the AINS real-time filter, and from post processing the AINS measurements.

Pressure control valve having an asymmetric valving structure

Abstract: The present invention describes, generally, a method and system for controlling the dynamics of an actuatable load functioning or operable within a servo or servo-type system, wherein the dynamics of the load are controlled by way of a unique asymmetric pressure control valve (10) configured to provide intrinsic pressure regulation. The asymmetric pressure control valve (10), which may be referred to as a dynamic pressure regulator because of its capabilities, utilizes different sized free floating spools that are physically independent of one another and freely supported in interior cavities of respective corresponding different sized valving components that make up the valve body (12) to regulate the pressures acting within the overall system between the control or pilot pressure and the load or load pressure. The dual spools of the pressure control valve (10), although physically independent of one another, function in cooperation with one another in an attempt to maintain a state of equilibrium in the system, namely to keep pressure acting on or within the actuator (the load pressure), or the feedback pressure corresponding to the load pressure, the same as the control or pilot pressure. Moreover, pressure regulation and control is intrinsic to the asymmetric pressure control valve (10) because of the configuration and function of the dual spools and the feedback system acting on the spools, thus eliminating the need for electronically or mechanically user controlled systems.

The error of a quasi-static approach in predicting fluid forces on the hand in unsteady conditions

Abstract: This study found that the quasi-static approach, which has been a major method for predicting the hand force in swimming since 1970s, led to errors in predicting the fluid forces acting on the hand in unsteady conditions. For examining unsteady flow conditions, the hand model was rotated in the flowing or non-flowing flume, and the fluid forces acting on the hand model and the dynamic pressure on the surface of the hand model were measured. The fluid forces were decomposed into the tangential (y-axis) and radial directions of rotation (z-axis), and the direction normal to the rotation plane (x-axis). The values of the dynamic pressure on the hand model showed the possibility of the generation of large vortices. The errors in predicting the fluid forces on the hand model just after the model rotation are likely to be due to the effects of the large vortices generated by the accelerating hand.

Combustion Oscillation Monitoring Using Flame Ionization in a Turbulent Premixed Combustor

Abstract: To achieve very low NOx emission levels, lean-premixed gas turbine combustors have been commercially implemented that operate near the fuel-lean flame extinction limit. Near the lean limit, however, flashback, lean blow off, and combustion dynamics have appeared as problems during operation. To help address these operational problems, a combustion control and diagnostics sensor (CCADS) for gas turbine combustors is being developed. CCADS uses the electrical properties of the flame to detect key events and monitor critical operating parameters within the combustor. Previous development efforts have shown the capability of CCADS to monitor flashback and equivalence ratio. Recent work has focused on detecting and measuring combustion instabilities. A highly instrumented atmospheric combustor has been used to measure the pressure oscillations in the combustor, the OH emission, and the flame ion field at the premix injector outlet and along the walls of the combustor. This instrumentation allows examination of the downstream extent of the combustion field using both the OH emission and the corresponding electron and ion distribution near the walls of the combustor. In most cases, the strongest pressure oscillation dominates the frequency behavior of the OH emission and the flame ion signals. Using this highly instrumented combustor, tests were runmore » over a matrix of equivalence ratios from 0.6 to 0.8, with an inlet reference velocity of 25 m/s 82 ft/ s . The acoustics of the fuel system for the combustor were tuned using an active-passive technique with an adjustable quarter-wave resonator. Although several statistics were investigated for correlation with the dynamic pressure in the combustor, the best correlation was found with the standard deviation of the guard current. The data show a monotonic relationship between the standard deviation of the guard current (the current through the flame at the premix injector outlet) and the standard deviation of the chamber pressure. Therefore, the relationship between the standard deviation of the guard current and the standard deviation of the pressure is the most promising for monitoring the dynamic pressure of the combustor using the flame ionization signal. This addition to the capabilities of CCADS would allow for dynamic pressure monitoring on commercial gas turbines without a pressure transducer.« less

Flow oscillation characteristics in conical cavity with multiple disks

Abstract: ac = speed of sound inside the cavity D = cavity depth f = frequency fn = predicted peak frequency kc = ratio of the average vortex convection speed to the freestream flow speed L = cavity length L=D = length-to-depth ratio of the cavity M1 = freestream Mach number n = mode number pref = reference pressure, 2 10 5 Pa q1 = freestream dynamic pressure r = recovery factor in temperature U1 = freestream velocity = phase constant between vortex shedding and the acoustic wave response in the cavity = specific heat ratio of the ideal gas f = power spectral density as function of frequency Introduction

An automatic water supply regulating system of washing machines

Abstract: The present invention involves a washing machine water-feed automatic governing system. It bases on full-automatic washing machine which has used magnetic valve as inlet valve and its water-inlet time is fixed, switches in a spell of auxiliary measuring water pipe which inside is equipped with pitot tube between the washing machine inlet valve exhaust pipe and washing cylinder, the Pitot tube is in vertical angle and its hemi-spherical head is opened with dynamic pressure channel mouth facing the flow direction of water inlet, the tube wall front end side is opened with static pressure channel mouth, the dynamic and the static pressure channel mouth extend to the end of pitot tube, the formed dynamic and the static pressure testing mouths are installed with pressure sensors for testing the dynamic and the static pressure of water-feed flow, the water pressure signals pass through signal amplification, analogue/digital conversion and is input into microcontroller, the microcontroller calculates the water inflow and thus determines if the water requirement is reached, and thereby controls the inlet valve closes. The present invention can adjust washing machines influent time automatically and overcome the impact from water-feed pressure changes to washing machine actual water inflow.

Exact pressure evolution equation for incompressible fluids

Abstract: An important aspect of computational fluid dynamics is related to the determination of the fluid pressure in isothermal incompressible fluids. In particular this concerns the construction of an exact evolution equation for the fluid pressure which replaces the Poisson equation and yields an algorithm which is a Poisson solver, i.e., it permits to time-advance exactly the same fluid pressure \textit{without solving the Poisson equation}% . In fact, the incompressible Navier-Stokes equations represent a mixture of hyperbolic and elliptic pde's, which are extremely hard to study both analytically and numerically. In this paper we intend to show that an exact solution to this problem can be achieved adopting the approach based on inverse kinetic theory (IKT) recently developed for incompressible fluids by Ellero and Tessarotto (2004-2007). In particular we intend to prove that the evolution of the fluid fields can be achieved by means of a suitable dynamical system, to be identified with the so-called Navier-Stokes (N-S) dynamical system. As a consequence it is found that the fluid pressure obeys a well-defined evolution equation. The result appears relevant for the construction of Lagrangian approaches to fluid dynamics.

Closed-Loop Control of Linear Supersonic Cavity Tones

Abstract: Experiments in a supersonic wind tunnel studied the behavior of acoustic tones introduced by open-loop forcing, and the ability of a closed-loop controller to suppress acoustic tones. The performance of pulsed-blowing and zero-net-mass actuators was documented. By independent changes in the wind tunnel static pressure and actuator supply pressure, we showed that the amplitude of disturbances input from the actuator is proportional to the pressure difference across the actuator, and scaled with the freestream dynamic pressure. The cavity used in this experiment at M = 1.86 responded linearly to the disturbance input from the actuators. Acoustic tone amplitudes in the cavity were linearly proportional to actuator input, and nonlinear interactions between different acoustic modes (such as the formation of combination modes) were not observed. Given that the system responded linearly to open-loop forcing and the amplitude of disturbances from the actuator exceeds background disturbance levels, then closed-loop control of the Rossiter tones should be feasible using standard linear control design tools. A simple gain-phase adjustable feedback controller is used to demonstrate linear closed-loop control.