Dynamic Pressure Measurements Research Articles

Investigation of the influence of rain on pitot-static measuring systems of unmanned aerial vehicles

AbstractFor unmanned aerial systems with a maximum take-off mass of up to 25 kg, simple pitot-static tubes are predominantly used to measure the aerodynamic speed. In this work, the influence of rain on this measurement is investigated using representative pitot tubes of different diameters. In wind tunnel tests, water droplets with a diameter of about 3 mm are generated at a flow velocity of 10 m/s, which hit the pitot tubes at the total pressure bore. The observed disturbances sometimes last several hours and are equivalent to a total failure of the measuring system during flight operations. Phenomena are identified that influence the measurement of dynamic pressure in rain. It can be shown that both capillarity and the momentum of the raindrops play a decisive role in the type, severity and duration of the disturbance due to their relative movement to the tube. The further course of the disturbance is also influenced by the evaporation of liquid, both on and in the tube. In flight tests under rain conditions, the findings of the wind tunnel tests were qualitatively confirmed and additional disturbance patterns were observed.

Synchronous measurement of wind pressure and flow field in wind tunnel: device, method and application

Accurate assessment of the relationship between flow field and surface wind pressure distribution around buildings in wind tunnel tests is crucial for understanding the interaction mechanism between wind and buildings. Despite notable technological advancements in dynamic pressure measurement and flow visualization, the acquirement of synchronous data on flow and wind pressure around buildings still faces challenges in terms of accuracy, cost, and operational complexity. Given this, a frame synchronization technique has been developed to collect flow field and wind pressure data based on particle image velocimetry and Scanivalve dynamic pressure measurement. Meanwhile, this study established a more precise correction method for the distortion effect of the synchronously measured wind pressure signal. Furthermore, the paper demonstrates the feasibility of synchronously measuring the flow field and the corrected wind pressure in time through the flow around triangular prism test. Experimental results indicate that the corrected wind pressure distribution on triangular prism surface is consistent with the temporal variations in instantaneous flow velocity and vorticity change, thereby verifying the reliability of the synchronous test system.

Electret mechano-sensor array integrated with tribopotential-modulated thin film transistors for precise spatiotemporal pressure perception

Spatiotemporal pressure perception is a key function of electronic skins. Electret mechano-sensors, as active sensors for E-skins, have garnered significant interest, with outstanding sensing performance in dynamic pressure measurement. However, their high output impedance poses a challenge in accurately and simply measuring low-frequency or static pressure distribution. Herein, we proposed an electret mechano-sensor array, in which each sensing cell is based on an electret sensor integrated with an IGZO TFT. The high input impedance of the TFT facilitates the sensor signal readout and enables the measurement of static pressure. The super-linear amplification feature of the TFTs improves the sensitivity and linearity of the sensors. An IGZO TFT layer with the lower electrodes of the electret sensor was fabricated through microfabrication process and assembled with a pre-charged electret film to achieve a mechano-sensor array with a high density. The fabricated TFT-integrated electret mechano-sensor array has achieved pattern detection and spatial tactile perception. Moreover, the sensor array can record spatiotemporal static pressure and arterial pulse waves simultaneously, exhibiting high resolution in detecting subtle changes and potentially offering various physiological information regarding the cardiovascular system. This work demonstrated that the proposed mechano-sensor array has capabilities for broad-scale pressure distribution detection in healthcare monitoring and human-computer interaction.

The dynamic response of a pressure transducer for measurements in water

Dynamic pressure measurements are indispensable in the field of fluid mechanics. Attaching tubing as a transmission line to the pressure transducer is often unavoidable but significantly reduces the usable bandwidth of the measurement system. Complex fluid-wall interactions and potential outgassing of air are present within systems with water-filled tubes. Comprehensive studies aiding researchers in selecting suitable transmission line parameters (i.e., material, length, and diameter) are not available. A simple calibration apparatus is designed for the frequency response characterization of multiple pressure transducers simultaneously applying a pressure step. The setup is thoroughly characterized and a detailed description is provided to optimize the bandwidth. A piezoresistive pressure transducer attached to water-filled tubes, as commonly used in hydrodynamic experiments, is characterized in the low-frequency range (i.e., f≤300\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$f \\le {300}$$\\end{document} Hz). Tube-related effects, such as length, diameter, and material are investigated. The impact of entrapped air within the tubing is analyzed. The feasibility of substituting water with silicone oil to fill the tubes is explored. To optimize the usable bandwidth of the pressure measurement system for dynamic applications, it is essential to maintain short tubing that is as rigid as possible and free from entrapped air. Pressure wave propagation speed is reduced by two orders of magnitude in elastic transmission lines made of silicone. Pressure corrections through dynamic calibration are challenging due to the system’s sensitivity to various parameters affecting the dynamic response.

Effects of doors on an open cavity flow at Mach number 6

Open cavities with different door-opening angles are investigated using high-speed schlieren visualization and dynamic pressure measurements in hypersonic flow with a freestream Mach number of 6. With the help of numerical simulations, the shear layer deformation and pressure increase in the cavities due to the impingement of the door-leading-edge shocks are identified via comparison with those in the cavity without doors. As the door-opening angle decreases from 90°, the shear layer above the forepart of the cavity is gradually raised by the high pressure in the cavity. When the door-opening angle decreases to 30°and 15°, the boundary layer on the upstream flat plate of the cavity separates, and separation shock is observed. The doors enhance the instability of the cavity flow and increase the pressure fluctuations in the cavities. A new oscillation pattern, referred to as coupled oscillation, is observed in the cases with separation on the upstream flat plate, in which the separation shock oscillates at the same dominant frequency as the flow inside the cavity. Compared with the cavity without doors, this coupled oscillation causes a lower oscillation frequency and a larger overall sound pressure level. Cross-correlation analyses between pressure signals indicate that the disturbances generated at the trailing edge of the cavity can propagate to the separation on the upstream flat plate and cause coupled oscillation of the separation shock. The fundamental frequencies of the coupled oscillations can be normalized to approximately the same Strouhal number as that of the cavity without doors. These findings support that the oscillation mechanisms of hypersonic cavities without and with doors are primarily dominated by acoustic feedback.

The characteristics of bubbly shock waves in a cavitating axisymmetric venturi via time-resolved X-ray densitometry

The bubbly shock-driven partial cavitation in an axisymmetric venturi is studied with time-resolved two-dimensional X-ray densitometry. The bubbly shock waves are characterised using the vapour fraction and pressure changes across it, propagation velocity, and Mach number. The sharp changes in vapour fraction measured with X-ray densitometry, combined with high-frequency dynamic pressure measurements, reveal that the interaction of the pressure wave with the vapour cavity dictates the shedding dynamics. At the lowest cavitation number ( $\sigma \sim 0.47$ ), the condensation shock front is the predominant shedding mechanism. However, as $\sigma$ increases ( $\sigma \sim 0.78$ ), we observe an upstream travelling pressure discontinuity that changes into a condensation shock as it approaches the venturi throat. This coincides with the increasing strength of the bubbly shock wave as it propagates upstream, manifested by the increasing velocity of the shock front and the pressure rise across it. Consequently, the Mach number of the shock front increases and surpasses the critical value 1, favouring condensation shocks. Further, at higher $\sigma$ ( ${\sim }0.84\unicode{x2013}0.9$ ), both the re-entrant jet and pressure wave can cause cavity detachment. However, at such $\sigma$ , the pressure wave likely remains subsonic. Hence cavity condensation is not favoured readily. This leads to the re-entrant jet causing the cavity detachment at higher $\sigma$ . The shock front is accelerated as it propagates upstream through the variable cross-section of the venturi. This enhances its strength, favouring cavity condensation and eventual shedding. These observations explain the existence of shock fronts in an axisymmetric venturi for a large range of $\sigma$ .

Determination of parameters generating the reference pressure in the primary level dynamic pressure measurement system based on the drop weight method

For some industries such as automotive, defence, aerospace, pharmaceutical manufacturing, dynamic pressure measurement is an important requirement. In a primary level dynamic pressure measurement system with a drop weight method, the dynamic pressure value is calculated using parameters such as the effective area value depending on the piston cylinder unit, the maximum acceleration value measured by a laser interferometer. On the other hand, the type of liquid used in the measuring head is another important factor affecting repeatability and providing ease of measurement. In this study, a new measurement head, piston and cylinders were designed, manufactured and the Taguchi method was used to accurately determine some parameters affecting the measurements in a dynamic primary pressure measurement system operating with the drop weight method. In the studies carried out, four pistons, four cylinders, four sampling frequency values and two liquid types were considered. By using the Taguchi method, the optimum parameters of the dynamic pressure measurement system with drop weight method were determined with only sixteen experiments instead of one hundred and twenty-eight.

Dynamic stress prediction for a Pump-Turbine in Low-Load Conditions: Experimental validation and phenomenological analysis

To meet the increasing demand for higher flexibility in hydropower, an operating range extension in an existing hydroelectric powerplant is considered. To this end, the dynamic flow and structural behavior of the low-head pump-turbine is investigated in turbine mode in partial load and deep partial load conditions, to evaluate the feasibility of this flexibilization due to the increased high cycle fatigue damage. In a first step, different numerical simulation approaches that combine fluid dynamics and structural dynamics are applied and compared to in-situ dynamic strain and pressure measurements on the impeller. As a result, the modelling requirements for a numerical workflow that leads to unmatched accuracy in predicting the broad-band dynamic stresses of deep partial load are identified. In a second step, the operating-point-dependent fatigue crack initiation spots are identified based on dynamic stresses. Herein, the emergence of an additional dominant critical spot near the blade leading edge is observed, which is unexpected for low-head pump turbines. Thanks to the detailed numerical flow and structural analyses, the root cause for the dynamic stress concentration is studied and the emergence of the new critical spot is understood. It turns out in deep partial load, that the main source of pressure oscillations on the impeller blade surfaces is the vortex-dominated flow detachment zone around the blade leading edge, which, in combination with the geometry of the investigated impeller, translates into the main stress oscillations. The results of this work were later used to extend the operating range of the hydroelectric powerplant from initially 25% to 100% power output to now 0% to 100%.

Turbulent particle-gas feedback exacerbates the hazard impacts of pyroclastic density currents

Causing one-third of all volcanic fatalities, pyroclastic density currents create destruction far beyond our current scientific explanation. Opportunities to interrogate the mechanisms behind this hazard have long been desired, but pyroclastic density currents persistently defy internal observation. Here we show, through direct measurements of destruction-causing dynamic pressure in large-scale experiments, that pressure maxima exceed theoretical values used in hazard assessments by more than one order of magnitude. These distinct pressure excursions occur through the clustering of high-momentum particles at the peripheries of coherent turbulence structures. Particle loading modifies these eddies and generates repeated high-pressure loading impacts at the frequency of the turbulence structures. Collisions of particle clusters against stationary objects generate even higher dynamic pressures that account for up to 75% of the local flow energy. To prevent severe underestimation of damage intensities, these multiphase feedback processes must be considered in hazard models that aim to mitigate volcanic risk globally.

ACCURACY AND BLOOD PRESSURE THRESHOLD CONTROL ANALYSIS OF UNATTENDED AUTOMATED OFFICE BLOOD PRESSURE MEASUREMENT: A CROSS-SECTIONAL STUDY BASED ON MULTICENTER POPULATIONS

Objective: The emergence of unattended automated office blood pressure (u-AOBP) measurement, facilitated by the flourishing development of electronic blood pressure monitors, has been proposed as a potential alternative or complementary approach for assessing patients’ blood pressure status within clinical settings. However, robust evidence is lacking to determine its application in diagnosing hypertension within the clinical practice in China. This study aims to compare u-AOBP values with standard office blood pressure data, assess the correlation between u-AOBP and diagnostic thresholds. Design and method: The study involved participants recruited from October 2023 to February 2024 in three hospitals: People's Hospital of Gongyi City in Henan Province, Nangong City Hospital in Hebei Province, and Fuwai Hospital of the Chinese Academy of Medical Sciences. Standardized validated upper arm blood pressure monitors were used to measure blood pressure. Baseline demographic data, anthropometric measurements, u-AOBP, and standard office blood pressure data were collected, along with additional examination results, including echocardiograms and 24-hour ambulatory blood pressure monitoring. Results: 1. The difference between u-AOBP and awake dynamic average blood pressure was 1.34 mmHg (95% confidence interval: 0.88-3.55 mmHg), and the difference was not statistically significant (P = 0.236). 2. The optimal cutoff values for diagnosing elevated blood pressure using u-AOBP, determined by ROC curve analysis based on awake dynamic blood pressure measurements, were 130.75/83.75 mmHg (sensitivity 89.73%, specificity 27.27%). 3. In participants with a dipper blood pressure diurnal rhythm, there was no statistically significant difference between standard office blood pressure and u-AOBP measurements (P > 0.05). However, in the group including non-dipper rhythm participants, standard office blood pressure was higher than u-AOBP by 5.84/4.98 mmHg (P < 0.05). Conclusions: 1. Unattended automated blood pressure measurements can reduce, but not eliminate, the white coat effect, with an optimal cutoff value for diagnosing elevated blood pressure determined as 130.75/83.75 mmHg. 2. In individuals with a normal dipper blood pressure diurnal rhythm, standardized u-AOBP values are equivalent to standard office blood pressure.

Energy quantification framework for underwater explosive loading into PVC foam cladded composite plates

This paper presents a novel approach for analyzing the effects of near-field underwater blast loading on composite marine structures. The operational requirements of these structures often expose them to blast or shock loading, which can lead to significant damage. The study focuses on the propagation of spherical blast waves and the subsequent secondary bubble collapse pulse that affects the structure under near-field underwater blast loading events. An analytical framework is developed to calculate the blast energies and structural energies during this complex loading event. The study further investigates the effect of applying a sacrificial cladding made of low-density closed-cell foam to the loading face of a composite panel. Experiments were conducted in a specialized facility to characterize the explosive-driven blast-loading and the subsequent interaction between the shock pressure front and the structure. Dynamic pressure measurements and high-speed imaging were utilized to capture the behavior of the composite panel under these extreme conditions. 3D digital image correlation was employed to analyze strain and deformation of the composite panel, while high-speed side view cameras captured the fluid-structure interaction during the blast and bubble collapse loading event. The results strongly indicate that the collapse of the explosion bubble is the dominant failure source in near-field underwater blast loadings. The analytical quantification of energy further corroborates the significant damaging effects of bubble collapse due to the buildup of after-flow energies during the bubble collapse duration. Furthermore, the inclusion of low-impedance elastic-plastic PVC foam cladding is shown to significantly mitigate the effect of blast loading on the composite structure.

A study on dynamic pressure sensor based on Pitot tube structure.

To meet the demand for the accurate measurements of the dynamic pressure of a shock wave, a composite dynamic pressure sensor design method is proposed based on the formation mechanism, propagation characteristics, special testing environment of the dynamic pressure, and Pitot tube structure. The dynamic pressure of the shock wave is evaluated by the total pressure and static pressure units installed in the composite sensor. FLUENT simulation software was used to analyze the aerodynamic characteristics of the dynamic pressure sensor, and parameters such as the structural size and inlet position of the sensor were determined. In response to the special experimental environment of the shock wave, the requirements for the dynamic pressure measurements under damage conditions were analyzed, and a dynamic pressure testing system was established. Dynamic pressure tests with four 2,4,6-trinitrotoluene [C7H5(NO2)3] equivalents of 1, 2, 15, and 20kg were carried out. The experimental results show that the proposed sensor design method can accurately and effectively measure the dynamic pressure signal, and the dynamic pressure gain multiple decreases with an increase in the proportional distance. This provides an effective testing method for evaluating the dynamic pressure damage effect of ammunition systems.

High-Speed and Error-Suppressed Fiber-Optic F–P System for Dynamic Pressure Measurement at High Temperature

High-Speed and Error-Suppressed Fiber-Optic F–P System for Dynamic Pressure Measurement at High Temperature

Pressure Sensors: Working Principles of Static and Dynamic Calibration.

This paper starts with an overview of the main principles used for pressure measurements, focusing on their usage in industrial applications' domains. Then, the importance of calibration procedures, namely, static and dynamic calibration of pressure sensors, is analyzed. Regarding calibration, it is important to note that there are several applications where the pressure signals to be measured can have large variations in short periods of time. In industrial applications, particularly in continuous production processes, generally, dynamic pressure measurements are less common; however, they are still required in several cases, such as control loops that are very sensitive to pressure variations, even if the frequencies of those variations are in the range of a few tens of hertz, or even lower. The last part of the paper presents the hardware and software of a flexible and low-cost static and dynamic pressure calibrator that also presents the capability to generate arbitrary waveform pressure signals for calibration and testing purposes. The proposed calibrator also includes the following advantages: remote pressure sensing capabilities that can be used to minimize calibration errors, such as those associated with capillary effects and pressure leakages; portability; and low cost. The paper ends with some experimental results obtained with the proposed calibrator.

Investigation of longitudinal self-excited combustion instability in a micromix hydrogen combustor

The increasing emphasis on low-carbon energy has heightened investigations into hydrogen combustion. This study focuses on the critical yet underexplored topic of thermoacoustic instabilities in micromix hydrogen combustors. We employ a newly designed micromix burner to explore the intricate relationships among acoustic modes, flame dynamics, and flow-vortex interactions. High-speed particle image velocimetry (PIV) and OH* chemiluminescence, supplemented by dynamic pressure measurements, are employed to capture dynamic behaviors and instability modes of the flame. Through thermoacoustic network analysis, we can identify two primary self-excited modes: a dominant low-frequency mode oscillating between 520 Hz and 565 Hz, and a secondary high-frequency mode surpassing 4400 Hz, originating from the hydrodynamic instability of the nozzle's jet flow. The low-frequency mode significantly influences the flame dynamics, generating a distinct longitudinal flame oscillation behavior. In particular, the inner premixed flame exhibits a periodic pattern of lifting and re-attachment phenomena. The outer diffusion flame, however, dynamically interacts with the outer shear layer (OSL) and the shed outer vortex rings (OVRs), which gives rise to notable deformations in the flame surface, manifesting as neck and swell structures propagating downstream with the OVRs. Furthermore, the dynamics of the OSL and OVRs are attributed to the fluctuations in the bulk flow velocity and local equivalence ratio at the nozzle exit, which are sustained by pressure oscillations induced by thermoacoustics. This presents important insights into the interplay between hydrodynamics and thermoacoustics in the formation of combustion instability in the micromix hydrogen combustor.

Two-phase flow regime identification using multi-method feature extraction and explainable kernel Fisher discriminant analysis

PurposeIdentifying the flow regime is a prerequisite for accurately modeling two-phase flow. This paper aims to introduce a comprehensive data-driven workflow for flow regime identification.Design/methodology/approachA numerical two-phase flow model was validated against experimental data and was used to generate dynamic pressure signals for three different flow regimes. First, four distinct methods were used for feature extraction: discrete wavelet transform (DWT), empirical mode decomposition, power spectral density and the time series analysis method. Kernel Fisher discriminant analysis (KFDA) was used to simultaneously perform dimensionality reduction and machine learning (ML) classification for each set of features. Finally, the Shapley additive explanations (SHAP) method was applied to make the workflow explainable.FindingsThe results highlighted that the DWT + KFDA method exhibited the highest testing and training accuracy at 95.2% and 88.8%, respectively. Results also include a virtual flow regime map to facilitate the visualization of features in two dimension. Finally, SHAP analysis showed that minimum and maximum values extracted at the fourth and second signal decomposition levels of DWT are the best flow-distinguishing features.Practical implicationsThis workflow can be applied to opaque pipes fitted with pressure sensors to achieve flow assurance and automatic monitoring of two-phase flow occurring in many process industries.Originality/valueThis paper presents a novel flow regime identification method by fusing dynamic pressure measurements with ML techniques. The authors’ novel DWT + KFDA method demonstrates superior performance for flow regime identification with explainability.

Performance Characteristics of a Rotating Detonation Combustor Exiting Into a Pressurized Plenum to Simulate Gas Turbine Inlet

Abstract The present study aims to experimentally characterize the performance of a rotating detonation combustion (RDC) system integrated with a pressurized downstream plenum to simulate the high-pressure inlet conditions of power-generating gas turbines. A thorough understanding of the operational behavior including wave mode behavior, static pressure profile along the combustor length, and dynamic features of pressure fluctuations is crucial for successful integration of RDC with the turbine. In this study, two RDC configurations are investigated, RDC with a constant area annulus and RDC with a converging nozzle. In both cases, the RDC flow exited into a plenum chamber kept at pressures varying from 155 kPa to 330 kPa. RDC was operated on methane and oxygen-enriched air to represent reactants used in land-based power generation. Experiments were conducted for the two RDCs configurations operated at three reactant mass flow rates (0.23, 0.32, and 0.46 kg/s). The RDC performance is characterized by time-averaged static pressure measurements, and wave velocity determined by ionization probes. In addition, dynamic pressure measurements were recorded both inside and near the exit of RDC channel to investigate wave interactions between RDC and downstream plenum. Results show that the RDC with the converging nozzle achieved superior performance while minimizing detrimental interactions with the reflected shock and/or acoustic waves from the downstream plenum.

Columnar-jet to wall-jet state transition in transversely excited swirling flow

The current work investigates the transition of a swirling jet between two flow states, namely, columnar-jet (CJ) and wall-jet (WJ) states, under the influence of external transverse acoustic forcing. Here, we have performed simultaneous time-resolved stereoscopic particle image velocimetry and dynamic pressure measurements to understand the structure and dynamics of these swirling jets under external forcing. It is observed that at low Reynolds number (Re), the swirl flow transitions from CJ to WJ state due to transverse forcing. And the flow returns to the CJ state when the acoustic is turned OFF. However, above a critical flow Re, the swirl flow does transition from CJ to WJ state when subjected to transverse forcing, but upon turning OFF the acoustics, the flow stays in the WJ state. Thus, the swirling flow demonstrates bistability in the flow states only above a critical flow Re. It is observed that upon forcing, there is an increase in the streamwise velocity fluctuations (u′x) near the centerline and in the radial velocity fluctuations (u′r) near the injector lip. This finding is also confirmed through spectral proper orthogonal decomposition analysis. In addition, it is observed that as the flow transitions from CJ to WJ state, the relative contribution of the convective term Ur¯∂Ur¯∂r toward the radial pressure gradient (∂P¯∂r) increases in comparison to the centrifugal force term (U¯θ2r). The study highlights the effect of acoustic-induced velocity fluctuations on the bistability of swirl flows over a range of flow Re.

A Method for Determining the Density and Velocity of Pulse Gas Flows of Millisecond Duration

An experimental setup for studying pulse gas flows within short periods (up to 1 ms) was developed and an experimental data processing method is presented. Based on high-speed frame interferometry data and the results of dynamic pressure measurements, the spatial and temporal distributions of the helium flow density and velocity are determined. The optimal method for reconstructing the spatial density distributions with consideration for the experimental errors is described. The presented method allows characterization of the gas flows with a density of more than 0.0001 kg/m3 and a velocity of more than 400 m/s.

Flexible Tactile Sensors Using AlN and MOSFETs Based Ultra-Thin Chips

This paper presents ultrathin chips (UTCs) based flexible tactile sensing system for dynamic contact pressure measurement. The device comprises of an AlN piezocapacitor based UTCs tightly coupled with another UTCs having metal-oxide-semiconductor field-effect transistors (MOSFETs). In this arrangement the AlN piezocapacitor forms the extended gate of MOSFETs. Both AlN piezocapacitor and MOSFET based UTCs are obtained by post-process reduction of wafer thicknesses to ~35μm using backside lapping. The performances of both UTCs were evaluated both before and after thinning and there was no noticeable performance degradation. The UTC-based AlN piezocapacitor exhibited six times higher sensitivity (43.79mV/N) than the thin filmbased AlN sensors. When coupled with MOSFETs based UTC, the observed sensitivity was 0.43N-1. The excellent performance, flexible form factor and compactness shows the potential of presented device in applications such minimal invasive surgical instruments where high-resolution tactile feedback is much needed.