Showing papers on "Dynamic pressure published in 2019"

Flexible piezoresistive sensor matrix based on a carbon nanotube PDMS composite for dynamic pressure distribution measurement

Abstract: . A highly flexible, piezoresistive sensor matrix based on a carbon nanotube (CNT) polymer composite is developed for pressure distribution measurement applications. With an overall height of about 400 µ m, the sensors can measure pressure directly, without any deformation elements, such as a cantilever or a deformation membrane. The measurement range is from 2.5 to 640 kPa. Both the position and the pressure of the applied load can be measured and visualized as a resistance change. The relative resistance measurement deviation of the data acquisition system is lower than 3 % for the resistance range of 610Ω to 380 k Ω . This corresponds to a systematic deviation of pressure measurement of less than 3 % in the measurement range. Besides the measurement of pressure, different sizes of loads can be detected as well. The developed fast and compact measurement system allows dynamic pressure measurement, such as gait analysis when used in an insole application.

Investigation of fluid field analysis, characteristics of pressure drop and improvement of heat transfer in three-dimensional circular corrugated pipes

Abstract: In this investigation, the computational technique is carried out to study flow behaviour analysis, pressure drop characteristic and enhancement of heat transfer in three-dimensions smooth pipe and circular corrugated tube (circular sectional area rings are inserted around the tube). Various rings are considered as 0.375, 0.5 and 1 mm. Water is chosen as working fluid and at the tube external surface uniform heat flux is applied. Numerical simulation is performed computational fluid dynamics method at range of Reynolds number from 1500 to 24,000. To calculate the process of governing equations and energy analysis equations in numerical calculations the pressure-based solver double precession is used. Numerical simulation outcomes are validated with available experimental results. Also, the results shown a good agreement between them. Result indicated that the dynamic pressure profile and velocity profile in corrugated tube is non-uniform as compared to profile in smooth pipe. This can be explained due to the corrugated rings around the tube can cause more unstable flow closed to tube wall. Results revealed that the high heat transfer enhancement take place under low mass flow is 0.56 litter per min and corrugate ring of 1 mm and it is equal 26.48%, 19.43 and 15.26% for corrugate ring of 1, 0.5 and 0.375 mm respectively.

The Effects of Solar Wind Dynamic Pressure on the Structure of the Topside Ionosphere of Mars

Abstract: We use Mars Atmosphere and Volatile EvolutioN observations of the upstream solar wind, and Mars Express observations of ionospheric electron densities and magnetic fields, to study how the topside ionosphere ($>$ 320 km) of Mars is affected by variations in solar wind dynamic pressure. We find that high solar wind dynamic pressures result in the topside ionosphere being depleted of plasma at all solar zenith angles, coincident with increased induced magnetic field strengths. The depletion of topside plasma in response to high solar wind dynamic pressures is observed in both weak and strong crustal magnetic field regions. Taken together, our results suggest that high solar wind dynamic pressures lead to ionospheric compression, increased ion escape, and reduced day-to-night plasma transport in the high-altitude nightside ionosphere.

Correlation analysis of separation shock oscillation and wall pressure fluctuation in unstarted hypersonic inlet flow

Abstract: The flow field in a hypersonic inlet model at a design point of M = 6 has been studied experimentally. The focus of the current study is to present the time-resolved flow characteristics of separation shock around the cowl and the correlation between the separation shock oscillation induced by the unstart flow and the wall pressure fluctuation when the inlet is in a state of unstart. High-speed Schlieren flow visualization is used to capture the transient shock structure. High-frequency pressure transducers are installed on the wall around both the cowl and isolator areas to detect the dynamic pressure distribution. A schlieren image quantization method based on gray level detection and calculation is developed to analyze the time-resolved spatial structure of separation shock. Results indicate that the induced separation shock oscillation and the wall pressure fluctuation are closely connected, and they show the same frequency variation characteristics. The unsteady flow pattern of the “little buzz” and “big buzz” modes are clarified based on time-resolved Schlieren images of separation shock. Furthermore, the appropriate location of the pressure transducers is determined on the basis of the combined analysis of fluctuating wall-pressure and oscillating separation shock data.

Development of a PVDF Sensor Array for Measurement of the Dynamic Pressure Field of the Blade Tip in an Axial Flow Compressor.

Abstract: Tip clearance flow in axial flow compressor is unavoidable and responsible for pressure losses and noise generation and influences the stability of the compressor. However, necessary flow measurement in the blade tip region is a great challenge due to the small gap width as well as the structure limitation. In this paper, a polyvinylidene fluoride (PVDF) piezoelectric-film sensor array is developed to capture the dynamic pressure field over the blade tip in an axial flow compressor. The PVDF sensor array with 40 evenly distributed sensing points is fabricated directly on a 30 μm thick aluminum-metalized polarized PVDF film through photolithography. Dynamic calibration of the sensor is accomplished using acoustic source as excitation and a microphone as a reference. The test pressure range is up to 3.5 kPa and the sampling frequency is 20 kHz. The sensor presents a high signal-to-noise ratio and good consistency with the reference microphone. Sensitivity, frequency response, linearity, hysteresis, repeatability as well as the influence of temperature are also investigated through the calibration apparatus. The calibration gives credence to the relevance and reliability of this sensor for the application in dynamic pressure field measurement. The sensor is then applied to an actual measurement in a compressor. The output of the PVDF sensor array is also compared with the results of common pressure transducers, and the features of the dynamic pressure filed are discussed. The results indicate that the PVDF sensor array is capable of the dynamic pressure field measurement over the blade tip, and superior to the conventional approaches in installation, spatial resolution, frequency response, and cost. These advantages indicate its potential broad application in pressure measurement, especially for the complex spatial surface or thin-walled structure, such as the blade surface and the thin casing wall of the compressor.

Shape Memory Polyurethane-Based Smart Polymer Substrates for Physiologically Responsive, Dynamic Pressure (Re)Distribution

Abstract: Shape memory polymers (SMPs) are an exciting class of stimuli-responsive smart materials that demonstrate reactive and reversible changes in mechanical property, usually by switching between different states due to external stimuli. We report on the development of a polyurethane-based SMP foam for effective pressure redistribution that demonstrates controllable changes in dynamic pressure redistribution capability at a low transition temperature (∼24 °C)-ideally suited to matching modulations in body contact pressure for dynamic pressure relief (e.g., for alleviation or pressure ulcer effects). The resultant SMP material has been extensively characterized by a series of tests including stress-strain testing, compression testing, dynamic mechanical analysis, optical microscopy, UV-visible absorbance spectroscopy, variable-temperature areal pressure distribution, Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray diffraction, differential scanning calorimetry, dynamic thermogravimetric analysis, and 1H nuclear magnetic resonance spectroscopy. The foam system exhibits high responsivity when tested for plantar pressure modulation with significant potential in pressure ulcers treatment. Efficient pressure redistribution (∼80% reduction in interface pressure), high stress response (∼30% applied stress is stored in fixity and released on recovery), and excellent deformation recovery (∼100%) are demonstrated in addition to significant cycling ability without performance loss. By providing highly effective pressure redistribution and modulation when in contact with the body's surface, this SMP foam offers novel mechanisms for alleviating the risk of pressure ulcers.

Simulation and experiment on pressure field characteristics of hydrostatic hydrodynamic hybrid thrust bearings

Abstract: This paper aims to improve the bearing capacity of hydrostatic thrust bearing under working conditions of high speed and heavy load; a new wedge-shaped structure opened on an edge of oil seal is put forward, the loss and insufficiency for hydrostatic bearing capacity are made up by using dynamic pressure, and then, hydrostatic hydrodynamic lubrication is realized.,Oil film three-dimensional models of unidirectional and bi-directional hydrostatic hydrodynamic oil pad are established by using UG. The oil film pressure fields of two kinds of oil pad are simulated by using ANSYS ICEM CFD and ANSYS CFX; the pressure fields distribution characteristics are obtained, and the effects of workbench rotary speed and bearing weight on pressure field are analyzed. Also, the experimental verification is made.,The results demonstrate that with an increase in workbench rotary speed, the oil film pressure of two kinds of hybrid oil pad increases gradually, and the maximum pressure of the bi-directional one accounts for 95 per cent of the unidirectional one when the load is constant. With an increase in load, the oil film pressure of two kinds of hybrid oil pad increases gradually, the difference between them is 9.4 per cent under the condition of load of 25 t when the rotary speed is constant.,The paper can provide theoretical basis for a structure design of hybrid thrust bearing under different rotary speed and load conditions, and compensate the shortage of static pressure-bearing capacity by using dynamic pressure, improve the stability of vertical CNC machining equipment.

Free-jet testing of a Mach 12 scramjet in an expansion tube

Abstract: Scramjet technology has the theoretical potential to provide air-breathing propulsion as a more efficient alternative to conventional rocket propulsion. Since the vehicle captures its oxidiser from the atmosphere — as opposed to carrying it like a rocket — the specific impulse can theoretically be increased by an order of magnitude, thereby increasing payload mass fractions. In this context, three- stage hybrid rocket-scramjet-rocket launch systems have shown to potentially provide a cost-effective and flexible solution for satisfying the requirements of the small-satellites market. However, to be economically feasible, the proposed scramjet-powered second stage would be reusable.Rectangular-to-Elliptical-Shape-Transitioning (REST) engines have shown to be a viable concept that can be integrated into access-to-space vehicles operating between Mach 5 and 12. The half-scale Mach 12 REST engine is a research scramjet specifically designed to operate in the last part of the ascent trajectory. Previous studies have demonstrated the ability of this design to successfully operate at equivalent flight conditions of Mach 11.6, 30 kPa dynamic pressure. However, tests have never been performed in freejet mode at the design conditions, as the facility which was used — the T4 reflected shock tunnel — was limited, like all RSTs by the extreme total pressure requirements of a Mach 12 flight. These limitations are aggravated by the even higher pressure necessary for pressure-length scaling, used to conserve the flow similarity between the half-scale experimental model and the flight engine.To overcome these limitations and allow freejet testing with pressure-length scaling, the use of expansion tubes has been proposed. These are currently the only kind of facility capable of producing these high-pressure requirements. Currently, the University of Queensland operates the X3 expansion tube, which is one of the few facilities worldwide with the potential to produce both the required total pressures and sufficiently long test times (up to 1.5 ms) to test an engine such as the Mach 12 REST engine.The goal of this thesis is to investigate and test for the first time, the Mach 12 REST engine in freejet mode, at fully replicated flight conditions. The study proposed using the X3 expansion tube, however, prior to this study the fastest scramjet test flow produced by X3 was Mach 10. Therefore, a significant part of this work tackles the extension of the X3 tunnel capabilities.A major element of the upgrade to X3 is a new hypersonic Mach 12 nozzle, which has been developed to allow higher Mach number flows and bigger core flow sizes. The nozzle profile has been designed via a parallel implementation of the Nelder Mead optimiser coupled with a RANS flow solver. The designed, fully contoured nozzle is 2.8 m long with an exit diameter of 573 mm.A Mach 12 operating condition for the facility has also been developed and tested, replicating the flight condition at Mach 12 and 50 kPa dynamic pressure. Experimental measurements and computation have revealed that the new test condition has a Mach number of 11.1 ± 0.9, 52.2 kPa dynamic pressure across a useful test time of 1.3 ms. The discrepancy to the target Mach number was due to an excessively thick boundary layer in the acceleration tube, which could only be addressed byiii shortening the X3 acceleration tube. This hardware modification was not feasible within the thesis timeline.Using the new nozzle and operating conditions in X3, the engine was first tested without pressure- length scaling to match previous experiments in the T4 facility, at a total enthalpy of 6 MJ kg−1 and a total pressure of 223 MPa. These experiments, the first under full freestream conditions, have demonstrated successful and robust combustion. The engine has been tested with two fuelling configurations, combustor only and inlet-combustor injection. The results confirmed that the latter was able to produce a significant increase in combustion. The engine was finally tested at the pressure-length scaled condition (for a total pressure of 450 MPa), where experiments indicated a reduced amount of combustion. A comparison with previous experimental data has shown similar flow structures and pressure levels, although discrepancies were noted in the position of the shock inside the combustor.The combined-injection scheme experiments initially produced engine unstarts. It was postulated that the acceleration tube air gas was igniting the inlet pre-fuelled hydrogen, thus unstarting the engine. A new accelerator gas substitution — replacing air with helium — was proposed and tested with successful and reliable results. This substitution was shown to facilitate the flow starting process during scramjet testing in expansion tube facilities.Expansion tubes have been shown to be able to carry out scramjet testing, however, they present several challenges such as a steady gradient in the freestream properties during the test time, unsteady disturbances, and the flow conditions are harsh on models. Nonetheless, comparisons to RST experiments steady numerical data indicate good agreement, showing that the data is still representative of the target steady conditions.In summary, this thesis demonstrates the potential of expansion tubes for high Mach number scramjet freejet testing, which addresses the limitations of reflected shock tubes, thus providing experimental data for conditions that were previously only achievable numerically or in flight. Furthermore, it provides the first data on the Mach 12 REST engine at design pressure and pressure-length scaled freestream conditions, showing robust combustion.

Research of a wind tunnel parameters by means of cross-section analysis of air flow profiles

Abstract: Wind tunnel is constructed. It is characterized by a high degree of airflow laminarization. The main constructive element of this aerodynamic tube is the laminarization module. It allows the destruction of turbulent fluxes by providing a homogeneous laminar flow. In order to evaluate the performance of the developed aerodynamic tube, a series of experimental studies was conducted in the range of air velocity of 10-50 m·s−1. To establish the laws of the distribution of flow parameters relative to the section the cross-sectional analysis method was used. It consists of forming a series of measuring planes that characterize the distribution of dynamic pressure and air flow velocity relative to the testing section. After that, the received experimental data are interpreted as three-dimensional graphic dependencies of the studied quantities. There is clearly observed a certain local area of stable values of dynamic pressure and flow velocity, after which they are sharply reduced in the direction of the walls of the section for testing. As a result of the analysis, a series of digital profiles of the distribution of dynamic pressure in the measuring planes of the testing section were obtained. Analysis of the obtained graphic dependencies allowed establishing of the uneven distribution of the dynamic pressure difference in the boundary layer zone along the inner perimeter of the test section is worth noting. Because of the side of the upper wall of the test section, the dynamic pressure difference is greater than the sidewall. This phenomenon is due to the difference in area of their blown air. Consequently, at a wall with a larger contact surface, a constant air stream experiences more loss of its kinetic energy than a wall with a smaller area. Especially this tendency is observed in the turbulent boundary layer.

Dynamics of random pressure fields over bluff bodies: a dynamic mode decomposition perspective

Abstract: Aerodynamic pressure field over bluff bodies immersed in boundary layer flows is correlated both in space and time. Conventional approaches for the analysis of distributed aerodynamic pressures, e.g., the proper orthogonal decomposition (POD), can only offer relevant spatial patterns in a set of coherent structures. This study provides an operator-theoretic approach that describes dynamic pressure fields in a functional space rather than conventional phase space via the Koopman operator. Subsequently, spectral analysis of the Koopman operator provides a spatiotemporal characterization of the pressure field. An augmented dynamic mode decomposition (DMD) method is proposed to perform the spectral decomposition. The augmentation is achieved by the use of the Takens's embedding theorem, where time delay coordinates are considered. Consequently, the identified eigen-tuples (eigenvalues, eigenvectors, and time evolution) can capture not only dominant spatial structures but also identify each structure with a specific frequency and a corresponding temporal growth/decay. This study encompasses learning the evolution dynamics of the random aerodynamic pressure field over a scaled model of a finite height prism using limited wind tunnel data. The POD analysis of the experimental data was also carried out. To demonstrate the unique feature of the proposed approach, the DMD and POD based learning results including algorithm convergence, data sufficiency, and modal analysis are examined. The ensuing observations offer a glimpse of the complex dynamics of the surface pressure field over bluff bodies that lends insights to features previously masked by conventional analysis approaches.

Compressible Fanno flows in micro-channels: An enhanced quasi-2D numerical model for laminar flows

Abstract: Micro-scale fluid systems are becoming common in many applications ranging from electronic cooling to refrigeration systems and more. One-dimensional numerical models represent a simple and fast tool for the design of such devices, yet they struggle to accurately predict the flow characteristics in compressible micro-flows. Under the adiabatic assumption, the elegant theory developed by Fanno allows models for the viscous compressible flow in constant cross-section channels to be easily built. Although reasonably accurate, these models suffer from drawbacks inherent to their being one-dimensional, as such they cannot take into account the local profiles of quantities like the velocity and the temperature. In cascade, this results into incorrect evaluations of other dependent quantities, such as the dynamic pressure and the fluid thermophysical properties. The mismatch turns large when the fluid compressibility becomes important. As the Mach number grows, the velocity profile changes, and so the friction factor, even though a reliable model for predicting this change is still missing. In fact, a constant friction factor throughout the channel is generally assumed, following the incompressible flow theory. Here, a set of correlations is proposed improving the 1D theory accuracy by taking into account the effects of the non-uniform velocity and temperature profiles in a quasi-2D fashion. A detailed analysis of the velocity profiles at different Mach numbers coming from a large set of CFD simulations results in a model for assessing the impact of compressibility on friction and other quantities. The numerical model proposed, being able to properly account for the compressibility effects, offers an improved tool for the design of micro-scale fluid systems. Extending the analysis to include heat transfer is not difficult as the effect of heat flux will be analogous to the effect of pressure drop due to friction.

Ion Pressure at the Auroral Precipitation Boundaries and Its Relationship with the Solar Wind Dynamic Pressure

Abstract: The data from the DMSP F7 satellite for 1986 are used to study the behavior of ion pressure at the boundaries of auroral precipitation. The study is based on 7489 satellite passages in the nightside sector of the auroral zone, including over 5000 passages in the 2100–2400 MLT sector. Ion pressure is determined as the average for 5 s of observations, which corresponds to a distance of ~40 km in the satellite trajectory portions adjacent to the precipitation boundaries. It is shown that the plasma pressure at the boundaries of auroral precipitation almost linearly increases at all levels of magnetic activity with an increase in the solar wind dynamic pressure (Psw). The pressure distribution as a function of MLT indicates that the precipitation boundaries, including the isotropy boundary, are not isobars, even at a low level of geomagnetic activity. The plasma pressure is maximal in the 22–24 MLT sector and decreases both in the morning and evening sides. The latitudinal position of the precipitation boundaries and the plasma pressure at the boundaries are found during all the phases of a typical substorm with an intensity of AL = –410 nT at its maximum. The latitudinal profile of ion pressure is constructed with respect to the isotropy boundary (IB) at the beginning of substorm. It is shown that, with an increase in dynamic pressure, there is not only a substantial increase in plasma pressure at the auroral precipitation boundaries but also a change in the latitudinal position of the boundaries themselves. As Psw grows, the latitude of the polarward boundary of the oval increases, while that of the equatorward boundary decreases. Despite the considerable expansion of the precipitation region, the latitudinal pressure gradient between the oval boundaries increases, even during quiet periods (average AL = –18 nT, IMF Bz = +1.4 nT) without any disturbances in the auroral zone, by approximately a factor of 2, from 0.06 to 0.12 nPa/deg.

Descriptions of Entropy with Fractal Dynamics and Their Applications to the Flow Pressure of Centrifugal Compressor

Abstract: In this study, some important intrinsic dynamics have been captured after analyzing the relationships between the dynamic pressure at an outlet of centrifugal compressor and fractal characteristics, which is one of powerful descriptions in entropy to measure the disorder or complexity in the nonlinear dynamic system. In particular, the fractal dynamics of dynamic pressure of the flow is studied, as the centrifugal compressor is in surge state, resulting in the dynamic pressure of flow and becoming a serious disorder and complex. First, the dynamic pressure at outlet of a centrifugal compressor with 800 kW is tested and then obtained by controlling the opening of the anti-surge valve at the outlet, and both the stable state and surge are initially tested and analyzed. Subsequently, the fractal dynamics is introduced to study the intrinsic dynamics of dynamic pressure under various working conditions, in order to identify surge, which is one typical flow instability in centrifugal compressor. Following fractal dynamics, the Hurst exponent, autocorrelation functions, and variance in measure theories of entropy are studied to obtain the mono-fractal characteristics of the centrifugal compressor. Further, the multi-fractal spectrums are investigated in some detail, and their physical meanings are consequently explained. At last, the statistical reliability of multi-fractal spectrum by modifying the original data has been studied. The results show that a distinct relationship between the dynamic pressure and fractal characteristics exists, including mono-fractal and multi-fractal, and such fractal dynamics are intrinsic. As the centrifugal compressor is working under normal condition, its autocorrelation function curve demonstrates apparent stochastic characteristics, and its Hurst exponent and variance are lower. However, its autocorrelation function curve demonstrates an apparent heavy tail distribution, and its Hurst exponent and variance are higher, as it is working in an unstable condition, namely, surge. In addition, the results show that the multi-fractal spectrum parameters are closely related to the dynamic pressure. With the state of centrifugal compressor being changed from stable to unstable states, some multi-fractal spectrum parameters Δα, Δf(α), αmax, and f(αmin) become larger, but αmin in the multi-fractal spectrum show the opposite trend, and consistent properties are graphically shown for the randomly shuffled data. As a conclusion, the proposed method, as one measure method for entropy, can be used to feasibly identify the incipient surge of a centrifugal compressor and design its surge controller.

High-Temperature Piezoelectric Pressure Sensors for Hypersonic Flow Measurements

Abstract: This paper presents a microelectromechanical-system (MEMS) piezoelectric pressure sensor for measurements in hypersonic flows at extreme temperatures (>1000 °C). 700-µm diameter diaphragms are surface- and bulk-micromachined and employ aluminum nitride as the sensing material due to its potential for high-temperature operation. Novelty claims include the following: (1) First demonstration of MEMS piezoelectric pressure sensor to capture hypersonic-flow-specific features in field measurements, including shock waves and second-mode instabilities associated with laminar-to-turbulent transition, (2) Successful audio capture while the sensor is immersed in a butane flame, demonstrating operation at extreme temperatures, and (3) First dynamic pressure sensor to include on-diaphragm thin-film platinum temperature sensors for high-temperature readout.

Vibration-induced pressures on a cylindrical structure surface in compressible fluid

Abstract: This paper unprecedentedly addresses the effect of vibrations of a cylindrical structure on dynamic pressures in a compressible and incompressible fluid situation. To obtain analytical solutions, the density of the fluid is simplified as a constant, but the rates of the density with respect to time and to space are considered as a dynamic and time-dependent function. In addition, the low velocity of the vibration is taken into account so the lower order terms are negligible. According to the assumption that the vibration at the boundary of the structure behaves as a harmonic function, some interesting and new analytical solutions can be established. Both analytical solutions in the cases of the compressible and incompressible fluid are rigorously verified by the calibrated numerical simulations. New findings reveal that, in the case of the incompressible fluid, dynamic pressure at the surface of the cylindrical shell is proportional to the acceleration of the vibration, which acts like an added mass. In the case of the compressible fluid, the pressure at the surface of the cylindrical structure is proportional to the velocity of the vibration, which acts as a damping. In addition, the proportional ratio is derived as ρ c .