Miniature Pressure Research Articles

A Model Test for the Influence of Lateral Pressure on Vertical Bearing Characteristics in Pile Jacking Process Based on Optical Sensors.

Photoelectric integrated testing technology was used to study precast piles during pile jacking at the pile–soil interface considering the influence of the earth and pore water pressures on its vertical bearing performance. The low temperature sensitive fiber Bragg grating (FBG) strain sensors and miniature silicon piezoresistive sensors were implanted in the model pile to test the changes of earth pressure, pore water pressure and pile axial force of the jacked pile at the pile–soil interface, and the influence of lateral pressure on pile axial force was studied. The test results showed that the nylon rod is feasible as a model pile. The FBG strain sensor had a stable performance and monitored changes in the axial force of the model pile in real time. The miniature earth and pore water pressure sensors were small enough to avoid size effects and accurately measured changes in the earth and pore water pressures during the pile jacking process. During pile jacking, the lateral earth pressure increased gradually in depth, and the lateral earth pressure at the same depth tended to decrease at greater depths. Lateral pressures caused the axial force of the pile to increases by a factor of 1–2, where the maximum was 2.7. Therefore, the influence of the lateral pressure must be considered when studying the residual pile stress.

Apparatus development for contact mechanics of energy pile-soil interface

An Energy Pile-Soil Interface Characteristic Apparatus (EPSICA) was developed to investigate the contact mechanics of the pile-soil interface. In the center of the apparatus, there is an energy pile model, around which different soil can be filled to simulate pile in different subsoil. The soil can be saturated. By applying loads on the top of the soil, the different depths were simulated. The temperature of energy piles was controlled by the cycling fluid with a water bath. The Pt100 sensors were installed in the pile and soil to measure the temperature changes. The miniature earth pressure cells were installed on the pile surface to measure the normal stress of the pile-soil interface. The FBG quasi-distributed optical fiber technology was used to measure the hoop strain to evaluate the circumferential deformation of the pile model. Taking the sand foundation as an example, the mechanical behavior of pile-soil contact behavior during the heating and cooling cycle was studied based on the temperature of pile and soil, normal stress of pile-soil interface and hoop strain of pile. The developed apparatus provides a new method for the study of thermos-mechanical behavior of energy pile.

Miniature Diamond-Based Fiber Optic Pressure Sensor with Dual Polymer-Ceramic Adhesives

Diamond is a good candidate for harsh environment sensing due to its high melting temperature, Young’s modulus, and thermal conductivity. A sensor made of diamond will be even more promising when combined with some advantages of optical sensing (i.e., EMI inertness, high temperature operation, and miniaturization). We present a miniature diamond-based fiber optic pressure sensor fabricated using dual polymer-ceramic adhesives. The UV curable polymer and the heat-curing ceramic adhesive are employed for easy and reliable optical fiber mounting. The usage of the two different adhesives considerably improves the manufacturability and linearity of the sensor, while significantly decreasing the error from the temperature cross-sensitivity. Experimental study shows that the sensor exhibits good linearity over a pressure range of 2.0–9.5 psi with a sensitivity of 18.5 nm/psi (R2 = 0.9979). Around 275 °C of working temperature was achieved by using polymer/ceramic dual adhesives. The sensor can benefit many fronts that require miniature, low-cost, and high-accuracy sensors including biomedical and industrial applications. With an added antioxidation layer on the diamond diaphragm, the sensor can also be applied for harsh environment applications due to the high melting temperature and Young’s modulus of the material.

An Investigation of Coolant Within Serpentine Passages of a High-Pressure Axial Gas Turbine Blade

Cooling flow behavior is investigated within the multiple serpentine passages with turbulators on the leading and trailing walls of an axial gas turbine blade operating at design-corrected conditions with accurate external flow conditions. Pressure and temperature measurements at midspan within the passages are obtained using miniature butt-welded thermocouples and miniature Kulite pressure transducers. These measurements, as well as airfoil surface pressure field data from a full computational fluid dynamics (CFD) simulation, are used as boundary conditions for a model that provides quantitative values of film-cooling blowing ratio for each film-cooling hole on the blade. The model accounts for the continuously changing cross-sectional area and shape of the channels, frictional pressure loss, convective heat transfer from the solid portion of the blade, massflow reduction as coolant bleeds out through film-cooling or impingement holes, compressibility effects, and the effects of blade rotation. The results of the model provide detailed coolant ejection information for a film-cooled rotating turbine airfoil operating at design-corrected conditions and also account for the highly variable freestream conditions on the airfoil. While these values are commonly known for simpler experimental geometries, they have previously either been unknown or estimated crudely for full-stage experiments of this nature. The better-quantified cooling parameters provide a bridge for better comparison with the wealth of film-cooling work already reported for simplified geometries. The calculation also shows the significant range in blowing ratio that can arise even among a single row of cooling holes associated with one of the turbulated passages, due to significant changes in both coolant and local freestream massfluxes.

Velocity–pressure correlation measurement based on planar PIV and miniature static pressure probes

This study aimed to measure pressure-related turbulence statistics such as the velocity–pressure or the pressure–strain correlations. To do so, the pressure field evaluation based on the velocity data measured by particle image velocimetry (PIV) was combined with direct single-point-measurement by miniature static pressure probes (SP-probe). The instantaneous pressure field was derived from the measurement results by PIV, and the pressure fluctuations associated with the large-scale vortex motion were extracted using the instantaneous pressure directly measured by the SP-probe as a reference signal. The measurement was taken in a turbulent near wake of a circular cylinder. After the validity of the instantaneous pressure evaluated from the PIV data was addressed, the velocity–pressure correlation and the pressure–strain correlation were investigated.

Macro-mechanical modeling of blast-wave mitigation in foams. Part II: reliability of pressure measurements

A phenomenological study of the process occurring when a plane shock wave reflected off an aqueous foam column filling the test section of a vertical shock tube has been undertaken. The experiments were conducted with initial shock wave Mach numbers in the range \(1.25\le {M}_\mathrm{s} \le 1.7\) and foam column heights in the range 100–450 mm. Miniature piezotrone circuit electronic pressure transducers were used to record the pressure histories upstream and alongside the foam column. The aim of these experiments was to find a simple way to eliminate a spatial averaging as an artifact of the pressure history recorded by the side-on transducer. For this purpose, we discuss first the common behaviors of the pressure traces in extended time scales. These observations evidently quantify the low frequency variations of the pressure field within the different flow domains of the shock tube. Thereafter, we focus on the fronts of the pressure signals, which, in turn, characterize the high-frequency response of the foam column to the shock wave impact. Since the front shape and the amplitude of the pressure signal most likely play a significant role in the foam destruction, phase changes and/or other physical factors, such as high capacity, viscosity, etc., the common practice of the data processing is revised and discussed in detail. Generally, side-on pressure measurements must be used with great caution when performed in wet aqueous foams, because the low sound speed is especially prone to this effect. Since the spatial averaged recorded pressure signals do not reproduce well the real behaviors of the pressure rise, the recorded shape of the shock wave front in the foam appears much thicker. It is also found that when a thin liquid film wet the sensing membrane, the transducer sensitivity was changed. As a result, the pressure recorded in the foam could exceed the real amplitude of the post-shock wave flow. A simple procedure, which allows correcting this imperfection, is discussed in detail.

Design and Optimization of Elastic Diaphragm in Miniature High-Temperature Pressure Sensor

The differential stress distribution of rectangular diaphragm with different sizes is simulated and analyzed using ANSYS. The results show that the maximal differential stress region on the rectangular diaphragm is located at the diaphragm center and the long side center, and also it gradually increases as the length-width ratio decrease. When the ratio is less than 1:2.2, the increase degree is not obvious and even falls slightly. According to this, the length-width ratio of the rectangular strain diaphragm was optimized as 1:2.2. Furthermore, the influence of stain diaphragm with different thicknesses and temperatures in differential stress distribution is discussed. It proves that the differential stress of the diaphragm is less affected by temperature, when the diaphragm thickness is properly chosen. The present results will provide the prerequisite for the design of miniature high-temperature pressure sensor in the future.

A Design of Amplifying Circuit Based on Pt Resistance Strain Pressure Sensor

This topic takes the miniature Pt resistance strain pressure sensor made by Institute of Electronics, Chinese Academy of Sciences, as the core sensing element, and designs corresponding high-precision, low cost, low power amplifying circuit so as to realize accurate detection of atmospheric pressure in time. In this topic, a new design of amplifying circuit is taken, which first connects the digital potentiometer to the bridge circuit to adjust its balance, and then amplifies the output signal of the bridge circuit once to ideal value. This design not only meets the requirement of measurement, but also is feasible and reduces the cost. At the same time, in order to improve the precision of the potentiometer adjusting the bridge balancing, paralleled resistances are creatively used beside the digital potentiometer and its influence to the bridge balance adjustment and the accuracy of the bridge measurement is analyzed in detail.

An investigation into the seismic behaviour of dams using dynamic centrifuge modelling

Dynamic response of dams is significantly influenced by foundation stiffness and dam-foundation interaction. This in turn, significantly effects the generation of hydrodynamic pressures on upstream face of a concrete dam due to inertia of reservoir water. This paper aims at investigating the dynamic response of dams on soil foundation using dynamic centrifuge modelling technique. From a series of centrifuge tests performed on model dams with varying stiffness and foundation conditions, significant co-relation was observed between the dynamic response of dams and the hydrodynamic pressures developed on their upstream faces. The vertical bearing pressures exerted by the concrete dam during shaking were measured using miniature earth pressure cells. These reveal the dynamic changes of earth pressures and changes in rocking behaviour of the concrete dam as the earthquake loading progresses. Pore water pressures were measured below the dam and in the free-field below the reservoir. Analysis of this data provides insights into the cyclic shear stresses and strains generated below concrete dams during earthquakes. In addition, the sliding and rocking movement of the dam and its settlement into the soil below are discussed.

Simultaneous Measurement of Velocity and Fluctuating Pressure in a Turbulent Wing-tip Vortex Using Triple Hot-film Sensor and Miniature Total Pressure Probe

We have developed a probe-system for simultaneous measurement of three velocity components and pressure in turbulent flows. A miniature total pressure probe is placed adjacent to the sensors of a triple hot-film probe in order to achieve the spatial resolution which is equivalent to that of the triple hot-film probe itself. The instantaneous static pressure is calculated from measured velocity and total pressure by means of a newly developed processing method based on the Bernoulli equation for unsteady flows. The measurements were undertaken in a turbulent wing-tip vortex flow. The look-up table method is employed for the calibration of the hot-film probe so accurate velocity data could be obtained over a wide range of the flow-attack angles. It is also demonstrated that the present probe-system is capable of measuring fluctuations in both velocity and pressure in the 20–650 Hz frequency range. The distribution of the fluctuating pressure obtained by this indirect method is in good agreement with the results from direct measurements of static pressure, demonstrating the promising performance of the present method. Furthermore, an improvement in the ability to make measurements of the velocity–pressure correlation across the wing-tip vortex is achieved. This improvement is possible because the effects of lateral velocity components are properly taken into account in the present formulation. The investigation regarding the transport equation budget for turbulent kinetic energy shows an anomalous structure of turbulence in this flow, mainly due to the meandering of the vortex, and the measurement of pressure diffusion is found to play an important role in the characterization of this kind of flow.

0229 熱線流速計と小型静圧プローブを用いた変動速度・圧力の同時測定(OS2-6 乱流の計測・解析・制御,オーガナイズドセッション)

0229 熱線流速計と小型静圧プローブを用いた変動速度・圧力の同時測定(OS2-6 乱流の計測・解析・制御,オーガナイズドセッション)

Enhancing Flow Field Measurements Through Adaptive Multidimensional Data Sampling

A way to gain insight into the flow field conditions in turbomachinery is by carrying out a series of point measurements in a cross section of the flow, for example, with a miniature multihole pressure probe. A problem commonly encountered in situations like these is the selection of a suitable measurement grid layout and density for obtaining all essential information in a cost-effective and timely manner. In order to achieve the latter, a novel adaptive multidimensional data sampling technique has been developed at Cranfield University. This paper describes the underlying principles of this technique, the algorithms utilized, and the results obtained during its successful application to data sets of two different flow fields in a high-speed research compressor.

Accelerating the Calibration of Multihole Pressure Probes by Applying Advanced Computational Methods

The miniature multihole pneumatic pressure probe is widely regarded as a cost-effective, easy-to-use, and accurate method for performing two- or three-dimensional flow field measurements in turbomachinery. The major downside to the use of these probes is that the influence of fabrication imperfections on probe characteristics necessitates an extensive and highly time-intensive and, therefore, costly calibration of each individual probe. Unless these probes can be fabricated to such standards that make individual probe calibrations superfluous, the only way to significantly reduce the time and costs associated with probe calibration is to shorten the calibration process. The latter is only possible if all essential information can be obtained from less calibration data. This paper describes an approach to the calibration of a series of multihole pressure probes in which advanced computational methods are used to make this possible. By exploiting the key features of a probe’s characteristic this approach requires only a fraction of the size of a conventional calibration database for the accurate modeling of the relationships between port pressures and flow conditions. As a result, calibration time and costs can be reduced without the sacrifice of quality.

Reply to the discussion by G.H. Lei and J.Y. Shi on "Vacuum and surcharge combined one-dimensional consolidation of clay soils"

We appreciate the discussers’ comments and suggestions. Based on their analysis, the discussers have concluded that equal settlements would be expected for soil specimens consolidated under the same vacuum or surcharge pressure. This is in agreement with the experimental results obtained by the authors. The discussers have suggested that a greater volume change may be expected for a soil specimen under a vacuum pressure than under a surcharge pressure of the same magnitude, which they attribute to the all-around contraction of the soil skeleton. However, the authors did not find a significant change in volume in the soil specimen under a vacuum or surcharge pressure of the same magnitude. To fully investigate and understand the difference in the volume change, the discussers have suggested a modification for the vacuum cell to include a sealing membrane for the soil specimen. Although the membrane may improve the measurement for the volume change, it will be very challenging to seal the specimen in the configuration of the vacuum cell described in the study. Having a more sensitive volume change tube in the current configuration may achieve a more accurate volume change measurement. To further understand the vacuum–surcharge consolidation mechanism, the discussers have suggested mounting miniature lateral earth pressure transducers on the inner cell wall and the bottom porous stone to monitor the total pressure changes during the consolidation process. The authors appreciate the suggestion and agree with the potential benefit of such transducers. This modification will be considered in the design of the second version of the vacuum cell. 771

Effect of pressure and interstitial atoms on magnetic properties of LuFe11Ti Intermetallics

Magnetisation and magnetocrystalline anisotropy of the LuFe11Ti intermetallics have been studied under pressure up to 1.2 GPa in temperatures from 5 K to 350 K using a miniature CuBe pressure cell and a SQUID magnetometer. A decrease of Fe-moment under pressure is compatible with the increase of Fe-moment in hydride and nitride of LuFe11Ti. A complex dependence of magnetocrystalline anisotropy on volume of the elementary crystal cell of LuFe11Ti and its hydride and nitride has been observed.

Magnetic Moment of Fe and Magnetocrystalline Anisotropy of Fe-rich Intermetallic Compounds Under Pressure

Magnetization and magnetocrystalline anisotropy of Fe-rich R -Fe intermetallics ( R =Y and rare earths) have been studied under pressure up to 1 GPa in temperatures from 5 K to 350 K using a miniature CuBe pressure cell and a SQUID magnetometer. A decrease of Fe-moment under pressure depends strongly on local environment parameters such as a local atomic volume, local coordination of Fe-atoms and hybridization. The pressure-induced changes of magnetocrystalline anisotropy energy are caused by both, the pressure decrease of magnetization M S and the pressure effect on the crystal electric field interactions. The pressure experiments allow to distinguish both the effects.

Miniature multihole pressure probes and their neural-network-based calibration

Miniature multihole pressure probes and their neural-network-based calibration

Development of a system for diagnosis of the Presurge State of a centrifugal compressor

Surging is an unacceptable event observed during operation of a centrifugal compressor (CC). The high probability of damage to the rotor, bearings, and seals during surging makes it necessary to utilize antisurge protection systems. The basic principle of the design of such systems is related to measurement of the output corresponding to the boundary of the surging event. Because of the multiparameter dependence of output on variable factors (gas intake parameters, rotation rate, etc.), a socalled "setting" is introduced, i.e., the increased output value at which the antisurge protection system will switch on. This limits the range of acceptable operation of the compressor. Another drawback of this method of designing the antisurge protection system is the necessity of precise measurement of the compressor output, which is somewhat complicated in many cases (and even impracticable, for example, for natural gas compressors). The proposed system of diagnosing the presurge state of CC is based on an analysis of the signs of nonstationary processes that precede the onset of surging. The experiments conducted [ 1] show that in the overwhelming majority of cases a rotating stall precedes surging in the casing of CC. This process usually arises near the surge boundary, and the antisurge protection system should be switched on when it appears. The design concepts of the proposed system were experimentally investigated in the Department of Compressor Design at St. Petersburg State Technical University. The experiments were conducted on a single-stage model of standard and promising CC with an impeller + diffuser + rotary elbow + reverse control apparatus scheme. Impellers (Im) of the closed type of different geometry combined with vaned (VD) and vaneless diffusers (VLD) with peripheral velocities of up to 280 rn/sec. A measurement complex developed at the SPSTU was used; it consisted of a miniature static pressure pulsation sensor installed on the wall of the diffuser; communication line; eight parallel channels with a memory volume of 68 kilowords per channel; a synchronization system with tracking of the measurement channels; a system for measuring the rotation system; and a minicomputer. Signals from a sensor positioned on the midline of the intervane channel at the end of the diffuser are given as an exampie of processing. The signals were analyzed using the correlation theory of random processes and methods of spectral analysis [2]. To exclude excess information, filtration with a band filter with a low cut-off frequency of 3 Hz and a high cut-off frequency of 100 Hz was conducted. The correlation functions were calculated with the equation

Experimental Investigation of Steady and Unsteady Flow Field Downstream of an Automotive Torque Converter Turbine and Inside the Stator: Part II—Unsteady Pressure on the Stator Blade Surface

The stator flow field of an automotive torque converter is highly unsteady due to potential and viscous interactions with upstream and downstream rotors. The objective of this investigation is to understand the influence of potential and viscous interactions of the upstream rotor on the stator surface pressure field with a view toward improvement of the stator design. Five miniature fast-response pressure transducers were embedded on the stator blade. The measurements were conducted at three locations near the leading edge and two locations near the trailing edge at the midspan location. The upstream flow field was measured using a fast response five-hole probe and is described in Part I of this paper. The experimental data were processed in the frequency domain by spectrum analysis and in the temporal-spatial domain by the ensemble-averaging technique. The flow properties were resolved into mean, periodic, aperiodic, and unresolved components. The unsteady amplitudes agreed well with the pressure envelope predicted by panel methods. The aperiodic component was found to be significant due to the rotor–rotor and rotor–stator interactions observed in multistage, multispool environment.

Capacitance pressure pickups

The results of experimental investigations of miniature capacitance pressure pickups are reported.