High-frequency Pressure Sensors Research Articles

Implementation Of Optical Diagnostics For Study Of A Non-Canonical Hypersonic Geometry

The study of shock/boundary-layer interactions on a non-canonical hypersonic geometry involves physical complexities not found on the canonical investigations that dominate the literature. The present case examines a cone-slice-ramp, which combines an upstream asymmetric flow expansion with a downstream three-dimensional compression ramp. Optical diagnostics of the off-body flowfield are a necessary complement to surface instrumentation including high-frequency pressure sensors and Temperature Sensitive Paint (TSP). Focused Laser Differential Interferometry (FLDI) measured the flowfield distribution of second-mode instability waves responsible for transition. Filtered Rayleigh Scattering (FRS) was used for flow visualization of the separation region and unsteady shear layer. Velocimetry through the separation shear layer was provided by Femtosecond Laser Electronic Excitation Tagging (FLEET) whereas Coherent Anti-Stokes Raman Scattering (CARS) measured the thermal profiles through multiple flow features generated by the interaction. These flowfield diagnostics detail the alterations in the shock/boundary-layer interaction as the flow state moves from laminar to transitional to turbulent conditions, revealing behaviors absent from canonical flows.

Oscillation Times in Water Hammer Signatures: New Insights for the Evaluation of Diversion Effectiveness in Field Cases

Diversion is a crucial technique for effectively improving shale reservoir production by creating more complex fracture networks. Evaluating diversion effectiveness is necessary to optimize the parameters in hydraulic fracturing. Water hammer diagnostics, an emerging fracturing diagnosis technique, evaluate diversion effectiveness by analyzing water hammer signals. The water hammer attenuation, as indicated by the oscillation time, correlates with the complexity of fracture networks. However, it remains unclear whether the oscillation time is associated with diversion effectiveness. This paper elucidates the relationship between the water hammer oscillation time and diversion effectiveness by taking the probability of diversion and the treating pressure response as the evaluation criteria. Initially, a high-frequency pressure sensor was installed at the wellhead to sample the water hammer signals. Next, the oscillation times were determined using the feature extraction method. Simultaneously, the probability of diversion and the treating pressure response were calculated using the cepstrum error function and treating pressure curve, respectively. Then, the relationship between the oscillation time and diversion effectiveness was analyzed. Finally, a rapid judgment method for evaluating diversion effectiveness based on the water hammer oscillation time was proposed. The results indicated a negative correlation between the probability of diversion and the oscillation time, with higher probabilities resulting in lower oscillation times. The oscillation times exhibited a negative correlation with the treating pressure response, including the treating pressure increases and diversion pressure spikes, wherein a greater pressure differential led to lower oscillation times. Drawing from the statistics of a shale gas horizontal well in Sichuan, a better diversion effectiveness is associated with fewer oscillations, demonstrating a negative correlation between the diversion effectiveness and the oscillation time in water hammer signatures. Finally, a rapid judgment method for evaluating diversion effectiveness was proposed, utilizing the 95% confidence interval of the mean oscillation time. This paper offers useful insights into evaluating diversion performance in field cases.

Enhanced gate-valve failure detection in water distribution networks using ML and pressure data

ABSTRACT This study introduces an innovative diagnostic approach for identifying gate-valve failures in water distribution systems. By implementing high-frequency pressure sensors upstream and downstream of the gate valves, we obtained detailed pressure data that are pivotal for fault diagnosis. We explored three distinct machine-learning algorithms and two data-handling techniques to ensure optimal performance in real-world applications. In our methodology, supervised learning algorithms are used to analyze pressure differentials and predict valve behavior. We rigorously tested these algorithms using both raw and feature-engineered data, and the results indicated the effectiveness of the Gaussian-naïve Bayes model with six extracted features. This approach enhances the precision and reliability of diagnostics in water distribution networks.

Relaminarization effects in hypersonic flow on a three-dimensional expansion–compression geometry

This experimental work explores the flow field around a three-dimensional expansion–compression geometry on a slender cone at Mach 8 using high-frequency pressure sensors, high-frame-rate schlieren, temperature-sensitive paint, shear-stress measurements and oil-flow visualizations. The $7^\circ$ cone geometry has a hyperbolic slice which acts as an expansion corner and suppresses the disturbances present in the upstream boundary layer. Downstream of the cone-slice corner, high-frequency boundary-layer disturbances attenuate in all cases. Under laminar conditions, second-mode instabilities from the cone diminish and lower-frequency second-mode waves develop on the slice at a frequency commensurate with the increased boundary layer thickness. For fully turbulent cases, the boundary layer over the slice shows evidence of a two-layered nature with a turbulent outer region and a near-wall region with strong attenuation of high-frequency disturbances and reappearance of lower-frequency instability waves. When a downstream compression ramp is added to the slice, the expanded boundary layer shows enhanced susceptibility to separation such that separation is observed at a $10^{\circ }$ deflection, which is smaller than expected for turbulent conditions. For a $30^{\circ }$ ramp, boundary-layer separation occurs further upstream where the heat flux contours show a decrease in heating that is characteristic of a transitional separation. These results demonstrate the effect of relaminarization caused by an upstream expansion on a subsequent shock-wave/boundary-layer interaction.

Experimental study of the effects of isolated roughness elements on the stability and transition of a hypersonic boundary layer on a flat plate

Surface roughness elements on hypersonic vehicles can cause early boundary layer transition, increasing wall skin friction and heat flux and affecting aircraft range and thermal protection systems. Accurate prediction of the transition caused by these roughness elements is crucial for the design of hypersonic vehicles. In this work, wind tunnel experiments on isolated roughness-induced boundary layer transition at Ma = 6 are conducted. Infrared thermography and high-frequency pressure sensors are utilized to investigate the effects of different roughness element configurations (cylindrical, diamond, ramp) on the hypersonic boundary layer instability and transition. The experimental results show that all three roughness elements can effectively enhance the generation of second mode waves and promote boundary layer transition. Compared to smooth surfaces, they exhibit similar frequency band range, faster growth, and earlier saturation. Among them, the ramp roughness element most effectively triggers the boundary layer transition, with a relatively small heat flux increase. Furthermore, bispectral analysis illustrates that all three roughness elements undergo self-interactions that lead to spectral broadening, ultimately resulting in boundary layer transitions.

Cavitation cloud of waterjet under double excitation

This study experimentally explores the interplay of active and passive excitation on double-excited cavitating waterjet clouds. High-speed imaging and high-frequency pressure sensors are used to characterize the impact of piezoelectric transducers for active excitation and nozzle lip geometries for strong, moderate, and weak passive excitation conditions. The analysis of pressure fluctuations revealed that under active excitation, the waterjet exhibited forced oscillations characterized by an amplitude amplification exceeding that of single passive excitation by an order of magnitude. High-speed imaging, combined with proper orthogonal decomposition, allowed us to observe an expansion in the volume, size, and effective standoff distance of cavitation clouds upon introducing active excitation across all passive excitation scenarios. The synergy between strong passive excitation and harmonized frequency with active excitation resulted in the most robust cavitation cloud development, characterized by the highest intensity.

Experimental study on low-frequency flow noise at the stern of a surface vessel induced by pulsating pressure

Understanding of the flow noise generated by high-speed ships is limited compared with that of underwater vessels. To better understand the low-frequency flow noise generated at the stern of high-speed vessels, a series of high-speed ship models were designed, and the flow noise induced by the pulsating pressure at their sterns was obtained in tests using 11 high-frequency pressure sensors located at the base of the stern in the longitudinal and transverse directions. The experimental setups and methods by previous researchers were considered. Systematic model tests were conducted under different velocity, side immersion depth (Tside), deadrise angle, and interceptor (which are widely used for high-speed vessels) conditions, and the sound pressure levels under different conditions were calculated. The general characteristics of the flow noise generated at the ship's stern, the influence of key factors, such as velocity, Tside, deadrise angle, and interceptor height, on the relative pressure, and the overall sound pressure level were then examined, providing useful insights for reducing the level of flow noise. The results are useful in obtaining a better understanding of the characteristics of the flow noise of high-speed ship induced pulsating pressure.

Experimental Investigation of the Hypersonic Boundary-Layer Transition Induced by the Wall-Mounted Cylinder

The flowfield structure, heat flux distribution, and pressure fluctuations of the wall-mounted cylinder-induced hypersonic boundary-layer transition are investigated at a 10 deg angle of attack. Experiments are conducted in a Mach 6 low-noise wind tunnel using the nanotracer-based planar laser scattering (NPLS) technique, temperature-sensitive paints (TSP), and high-frequency pressure sensors. First, the streamwise and spanwise NPLS images, TSP results, and power spectral density results of isolated cylinders at different heights show that with the increase of the cylinder height , the size of the separated region and the spanwise width of the horseshoe vortex increase, and the transition moves forward. Second, the flowfield structure and wall heat flux distribution around the streamwise cylinder arrays are investigated. The results demonstrate that the downstream cylinder will destroy the development of the hairpin vortex in the upstream cylinder wake but will expand the horseshoe vortex to both sides, increasing the influence area of the cylinder.

Suppression characteristics of multi-layer metal wire mesh on premixed methane-air flame propagation

Metal wire mesh is widely used in the energy industry for its excellent protective properties as a fire stopping and explosion isolating material. In this study, the suppression characteristics of different layers of metal mesh on the dynamic behavior of premixed methane-air flame propagation were studied experimentally. A high-speed photographic schlieren system was used to photograph the explosion process to capture the changes in the microstructure of the flame, and high-frequency pressure sensors and micro-thermocouple measurements were used to capture the flame explosion pressure and temperature. The experimental results show that the suppression effectiveness of wire mesh is a reflection of the coupling of explosive flame propagation behavior and combustion state in the pipe. Increasing the number of mesh layers and mesh density can destroy the microstructure of the premixed methane-air flame front and hinder the progress of flame propagation. Increasing the number of wire mesh layers will delay the peak time of premixed flame propagation speed and reduce the peak speed values of flame propagation. Wire mesh has a pronounced attenuation effect on premixed flame temperature and explosion overpressure. The maximum flame temperature attenuation rate is 34.99%–60.95%, and the maximum explosion overpressure attenuation rate is 33.70%–74.02%. And the suppression effect is greatly enhanced as the increase of mesh layers.

Experimental and numerical analyses of the thermodynamic and mechanical performance of an oil-injected and economized 4/6 twin-screw compressor

To advance oil-injected twin-screw compressors, it is necessary to understand and model the complex physical phenomena occurring during the compression process (e.g., mass and heat transfer mechanisms) as well as analyze the mechanical behavior of the compressor (e.g., rotordynamics, bearing loads, variation of clearance gaps). To validate these models, the in-chamber compression process as well as mechanical loads need to be accurately measured. This paper presents a comparison between experimental results and numerical modeling of a 4/6 oil-injected twin-screw compressor with slide-valve part-load modulation and economization. The compressor has been equipped with high-frequency pressure sensors, load-cells at the bearings and torque sensor on the main rotor. Bearing forces are analyzed to quantify and validate the experimentally obtained axial force data. The validated model can later be used to analyze the mechanical performance of the compressor, such as bearing loss computation. This study also discusses isentropic and mechanical efficiencies computed for the various data points.

Experimental study of sharp noise caused by rotating detonation waves

Previous studies of rotating detonation engines (RDEs) focused on combustion, heat transfer, and propulsion, but not noise, which is considered here. High-frequency pressure sensors, such as dynamic sensors, are often used as contact measurements to determine the detonation pressure and rotating detonation cycle time, but they obtain data for only a few seconds. Here, a simple and inexpensive acoustic measurement method is used to obtain the high-frequency sound pressure of the detonation and cycle time over more than a few hours and is not affected by high-temperature products. The results show that data of non-contact acoustic measurements, which can reflect the rotating detonation characteristics, agree well with those of picocoulomb pressure sensors and high-speed imaging. The production mechanism of sharp noise caused by rotating detonation waves is analyzed theoretically and compared with experimental results. Kinematic equations for vibrations are derived, and disturbance trajectories caused by oblique shock waves are found to be Archimedes spirals. This constitutes the first study on noise from RDEs. The study also promotes acoustic measurements, which have rarely been used to study RDEs.

Numerical Study on Improved Geometry of Outlet Pressure Ripple in Parallel 2D Piston Pumps

Because the axial piston pump is often used in the aerospace and aviation fields, it is necessary to pay attention to its outlet pressure and flow characteristics. The parallel 2D piston pump proposed, based on the axial piston pump, has no structural flow ripple because it has a rail with a uniform acceleration and deceleration. Now, the pump is used in the special working conditions of the aerospace field, and it is required to meet the rated flow of 50 L/min, the rated load of 8 MPa, and an extremely low-pressure ripple. Based on CFD technology, this paper studies the pump’s outlet flow and pressure ripples through numerical simulation. According to the causes of the outlet pressure ripple, an improved geometry is determined to further reduce the outlet pressure ripple. Using a high-frequency pressure sensor to measure the outlet pressure ripple of the optimized pump prototype, it was found that the outlet pressure ripple rate of the prototype was only 6%. The parallel 2D piston pump has been proved by the simulation and test that its outlet pressure ripple is extremely low. However, it is not effective to reduce the outlet flow ripple by increasing the pre-pressure and reducing the backflow. In parallel 2D piston pumps, it is still necessary to find a new method to further reduce outlet pressure and flow ripples.

Delaying hypersonic boundary layer transition using forward-facing step arrays: An experimental work

Our previous research has demonstrated that a single forward-facing step (FFS) could delay the hypersonic boundary layer transition on a cone [Xu et al., “Influences of steps on the hypersonic boundary-layer transition on a cone,” AIAA J. 59, 439–446 (2021)]. This paper aims to further this study by investigating the control effects of FFS arrays on the hypersonic boundary layer transition on a 7° half-angle sharp cone. Experiments are conducted in a Mach 6 wind tunnel using nano-tracer-based planar laser scattering techniques and high-frequency pressure sensors. Cases with smooth surfaces, single FFS, or FFS arrays with different spacing and step heights are studied for comparison. The results show that FFS arrays present a better performance on stabilizing the second mode wave and delaying the transition than a single FFS. Notably, the spacing and height between and of the steps also play an important role in the delay effect. For the cases studied, a better control effect can be achieved using FFS arrays spaced at a larger distance or with step height increasing along the flow direction. Moreover, FFS arrays could restabilize the second mode wave that has been amplified by the upstream backward-facing step.

An experimental study on steam explosion of a small melt jet falling into a water pool

To address the mechanisms and influential factors of steam explosions which may occur during severe accidents in a nuclear power plant (NPP), the VULCAN apparatus is designed and built to investigate the characteristics of a steam explosion when molten material falls into a water pool. The test facility is composed of a high-speed measurement system and an induction furnace which enables preparation and delivery a small melt jet at temperature up to 1500 ℃. In the first campaign of tests, tin is employed as the simulant of melt material, and the steam explosion process and pressure signals of a small molten tin jet falling into a deep water pool are recorded by a high-speed camera and a high-frequency pressure sensor, respectively. Debris particles from part test are collected and sieved for analysis of morphology and size distribution of the particles. Multiple occurrences of steam explosion are observed during the traveling of the melt jet into the water pool, with several cycles of expansion–contraction in each occurrence of steam explosion. The time interval between two occurrences is around 80 ms and between two cycles is around 4 ms. For the melt mass ranging from 20 to 140 g in the present study, it is found that the number of steam explosion occurrences increases with the melt mass. Both the pressure impulse and the conversion ratio of steam explosion increase with melt mass. However, the pressure impulse and conversion ratio do not have a monotonic relation with melt superheat, and the conversion ratio increase with melt superheat when it is below a threshold (370℃), but decrease above the threshold.

Effects of steps on the hypersonic boundary layer transition over a cone at 10° angle-of-attack

In a previous research on the hypersonic boundary layer transition over a sharp cone at 0° angle-of-attack (AoA), we concluded the different effects of the forward-facing step (FFS) and the backward-facing step (BFS) on the transition [Xu et al., AIAA J. 59, 439–446 (2021)]. This further study intends to examine if the conclusion still maintains after changing the nose bluntness and the angle-of-attack of the cone. Experiments are conducted in a Mach 6 wind tunnel using nano-tracer-based planar laser scattering techniques, temperature sensitive paints, and high-frequency pressure sensors. The results show that although the FFS delays the boundary layer transition while the BFS promotes the transition at AoA = 0°, a completely different pattern is observed at AoA = 10°, the FFS significantly promotes the transition, while the effect of the BFS appears only weakly to advocate the transition. Noteworthy, the nose bluntness will not change the effects of the BFS/FFS on the transition.

An experimental study on the effect of the flaring rate on flame dynamics in open pipes

Under the condition that the gas composition constant equivalence ratio is Φ = 1, and the initial temperature and initial pressure are T0 and P0, respectively, the experimental study of the premixed gas flames with different hydrogen doping ratios (φ = 10%–40%) is different. The behavior and shape change of propagation in the flaring rate pipe (ƞ = 1.0–0.25). The study found that the pre-mixed gas flame in the flared pipe has undergone more complicated shape changes than other studies. One of the outstanding findings is that the tulip flame appeared twice in this open pipe experiment. And through the high-speed camera and high-frequency pressure sensor to obtain the tulip flame picture and the pressure change in the combustion chamber, comprehensive analysis of the experimental results, and the results show that every appearance of the tulip flame is accompanied by the deceleration of the flame front and the increase of overpressure in the combustion chamber.

Sensor placement for robust burst identification in water systems: Balancing modeling accuracy, parsimony, and uncertainties

Urban water systems are seeing an uptake in using advanced sensing technology. Incorporating sensors for monitoring water distribution systems (WDSs) provides promising benefits to water utilities by enabling a shift from reactive to proactive pipe failure detection and from delayed water loss management to automatic sense-and-respond capabilities. Despite the opportunities that new sensing technologies create, a budget-constrained utility is challenged with identifying sensing locations in the WDS that will maximize information gain. To address this gap, this paper studies the problem of optimal placement of high-frequency pressure sensors in WDSs for pipe burst identification. This paper proposes a sensor placement strategy to address the challenges of data and modeling uncertainty by incorporating robust representation and tolerance analysis into an optimization framework with the objective of achieving the best detection and identification of burst events. Transient simulations are first used to predict system’s response to burst events, demonstrating the importance of modeling accuracy over approximation methods. A robust event representation approach is then presented to summarize system response to pipe bursts using signature matrices. Subsequently, the identification problem is cast as a minimum test cover problem when the number of available sensors is unlimited, and as the maximum covering test problem when the number of available sensors is limited. The optimization problems are then formulated and solved using mixed integer linear programming. Four complementary metrics are suggested to evaluate the performance of the sensor placement designs. Multiple criteria decision analysis is then applied to select the placement design while balancing information gain and cost. The results show that incorporating more information can improve event identification, but sufficient accuracy of the extracted information is required to accrue the benefits.

Influences of Steps on the Hypersonic Boundary-Layer Transition on a Cone

The influences of steps on the hypersonic boundary-layer transition on a cone are investigated in a hypersonic quiet wind tunnel, using high-frequency pressure sensors and nano-tracer-based planar laser scattering (NPLS) techniques. The high-frequency surface pressure fluctuations are analyzed using power spectral density analysis, band-pass filtering, and cross-correlation calculation. Quantitative analysis of the NPLS images is carried out based on the grayscale information and time interval. The results demonstrate that the second-mode wave amplitude increases initially and then drops along the streamwise, whereas the characteristic frequency decreases monotonously. However, the second-mode wave amplitude in the 0.4 mm () and 0.6 mm () forward-facing step models is constantly rising, and the obvious second-mode wave first appears closer to the downstream than the smooth cone, which suggests that the forward-facing steps could suppress the second-mode disturbances and shifts the transition downstream. Nonetheless, there is only a clear promotion effect when the height of the forward-facing step is 1.6 mm (). In addition, the backward-facing step could destabilize the boundary layer and shift the transition upstream, and this effect is enhanced by increasing the step height.

Visual experimental investigation on initiation process of H2/air rotating detonation wave in plane-radial structure

Using visual observation methods, assisted by synchronous measurement with high-frequency pressure sensors and ion probes, the initiation process of the plane-radial rotating detonation combustor under different operating modes are revealed. Results show that, the H2/air rotating detonation wave (RDW) cannot be obtained directly by the low-energy spark plug owning to its low ignition energy. The RDW initiation processes under different modes are similar, which undergo the following processes: ignition, deflagration, chaotic turbulent flame acceleration (deflagration to detonation transition), unstable detonation, and stable rotating detonation. For multi-wave mode, the collision and mode switching mostly appear to occur in the initiation. The chaotic turbulent flame development process is further analyzed. The reactants’ continuous injection and accumulation to a certain height is an important prerequisite for RDW initiation and stable propagation. The radial propagation of turbulent flames and collision promote the formation of hot spots, and the development of hot spots in reactants layer is an essential condition for the formation of circumferential flame.

Experimental research on methane/air explosion inhibition using ultrafine water mist containing methane oxidizing bacteria

In order to deeply understand the inhibitory effect of ultrafine water mist containing methane-oxidizing bacteria on methane explosion, a small-sized semi-closed visual experimental platform was built. Five different application mist amounts (0.7 mL, 2.1 mL, 3.5 mL, 4.9 mL, 6.3 mL) of ultrafine water mist containing methane-oxidizing bacteria on 9.5% methane explosion were studied experimentally. Ultrafine water mist was generated by the ultrasonic atomization generator, and mist size was measured by a winner319 laser particle size analyzer. During the methane explosion, a high-frequency pressure sensor collected pressure change data, and a high-speed camera recorded the flame development process. The results indicated that the maximum explosion overpressure (ΔPmax) decreased with time, and the arrival time of the maximum explosion overpressure (ΔPmax) delayed. The appearance time of the “tulip” shaped flame delayed, and the flame propagation speed decreased. The ultrafine water mist and deposition can effectively inhibit the methane explosion. The explosion suppression effect of the second step spraying water mist was better. The improvement of the explosion suppression effect of the ultrafine water mist containing methane-oxidizing bacteria was attributed to the degradation effect of the methane-oxidizing bacteria. Under long-term degradation, methane-oxidizing bacteria in water mist play a role in inhibiting methane explosion.