Fast Pressure Transducers Research Articles

Spectral and modal analysis of a cavitating flow through an orifice

Cavitation phenomena, produced when a flow is accelerated through a restriction, are of fundamental importance because of the large pressure oscillation they induce on pipelines. This paper presents an experimental investigation of various cavitation regimes produced at the exit of an orifice and its downstream propagation and attenuation. A cylindrical and a conical orifice are investigated over a range of cavitation number σ=0.2-1, keeping the ratio between saturation pressure (Psat) and downstream pressure (Pdw) at two different values ξ=Psat/Pdw=0.05,0.3. The range of operating conditions allows to investigate cavitation from the inception to the cloud, the developed, and the super-cavitation regime.For each configuration, the experimental analysis includes flow rate measurements, pressure signals via fast pressure transducers, and high-speed videos. The videos are analyzed using Multiscale Proper Orthogonal Decomposition (mPOD), to extract the coherent patterns that arise during the cloud cavitation and the developed cavitation regimes.The simultaneous analysis of the high-speed video in the proximity of the orifice and the time-resolved downstream pressure signal allows highlighting the effect of the cavitation intensity on the downstream evolution of these fundamental flows.

Experimental investigation on detonation dynamics through a reactivity sink

This article reports on an experimental investigation into dynamical behaviours of detonation in non-uniform mixtures, generated from stoichiometric propane–oxygen, oxygen and ethane, with initial temperature and pressure 290 K and 20 kPa, respectively. Composition gradients are parallel to the direction of detonation propagation, with an equivalence ratio (ER) that first decreases from lean values and then increases to rich ones. Composition distributions are characterized according to the depth of the ER sink. Gradients are generated in a 50 × 50-mm2-square cross-section and a 665-mm total length chamber. The mixture components are injected separately in the pre-evacuated chamber in their order of decreasing density through porous plates at the chamber top-end to ensure planar filling of the chamber. Non-uniform distributions are then precisely controlled as a function of time by means of optical oxygen sensors. A Chapman–Jouguet (CJ) detonation is transmitted at the chamber bottom-end from a 3.6-m-long driver tube. Fast pressure transducers, sooted plates and Schlieren visualizations coupled with high-speed cameras are used to characterize the longitudinal velocity, cellular structure and transmission, failure and re-initiation mechanisms of the detonation front. Shallowest ER sinks produce the supercritical transmission mode of the CJ detonation with continuous adaptation of velocity and multicellular structure to local composition. Deepest sinks lead to the subcritical behaviour characterized by sudden detonation failure from shock-flame decoupling when ER decreases, and without detonation re-initiation when ER increases again. Intermediate sink depths generate critical behaviour with detonation re-initiat ion at chamber walls from expanding combustion kernels and reflected transverse Mach waves and then from SWACER retro-active mechanism. An elaboration of the failure criterion used in a previous study is found to well predict conditions for shock-flame decoupling.

Experimental Investigation of Fracturing With Propellant in a Large Sandstone Block

This article, written by Special Publications Editor Adam Wilson, contains highlights of paper OTC 27563, “Experimental Investigation of Propellant Fracturing in a Large Sandstone Block,” by Sahil Malhotra, SPE, Peggy Rijken, and Alicia Sanchez, Chevron, prepared for the 2017 Offshore Technology Conference, Houston, 1–4 May. The paper has not been peer reviewed. Copyright 2017 Offshore Technology Conference. Reproduced by permission. Propellants have been used in oil and gas wells to assist with perforating and creating near-wellbore stimulation. Propellants are electrically ignited at the perforated interval. Upon ignition, they rapidly create a large amount of gas, and the pressurization leads to breakdown of the formation. Hypotheses suggest that the pressurization leads to the creation of multiple fractures. This paper describes an experimental study with a new propellant and aims to understand the pattern of fracture creation with these propellants. Introduction The fracture patterns created with propellant can include biwing fractures (in the direction perpendicular to the minimum principal stress), multiple/radial fractures, and explosive fractures, depending on the pressurization rate, as demonstrated in multiple small-scale experiments. A large-scale block test had been conducted previously to observe fracture patterns with the propellant Arcite 368M. The test resulted in the creation of a dominant biwing fracture in the direction perpendicular to the minimum principal stress. This paper presents an experimental study aimed at comparing the performance of a second-generation propellant with that of Arcite 368M. The goal is to determine if the propellant provides a higher pressurization rate and if multiple fractures can be obtained with the second-generation propellant. Laboratory Setup and Experimental Procedure A 30×30×54-in. Colton sandstone block was prepared with a 2-in.-diameter wellbore and loaded into a triaxial test frame. The openhole section of the borehole was etched with five small V-notches (2-in. long), spaced 60° azimuthally and 2 in. longitudinally. A small propellant assembly was centralized in the wellbore adjacent to the openhole section. The propellant assembly, integrated with an ignition system, was sealed with a water- and pressure-tight covering. The propellant charge was 1 in. in diameter and 0.5 in. long. Multiple yard tests in which propellant charges were ignited in a confined chamber were conducted to determine the appropriate size of the propellant. The size of the propellant charge was reduced until the peak pressure was less than 10,000 psi, which had been determined to be the safe limit for the experiment to be performed in the triaxial test frame. The wellbore was instrumented with a fast pressure transducer (recording at 10 kHz) to record the pressure transient caused by the propellant burn and subsequent fracturing events. In addition, the block was instrumented with six pressure/timing probes (also recording at 10 kHz). The purpose of the probes was to indicate arrival timing of the fracture tip, thus enabling determination of the fracture growth rate and symmetry.

Development of Instabilities Generated by Freestream Laser Perturbations in a Hypersonic Boundary Layer

A controlled, laser-generated perturbation was created in the freestream of the Boeing/U.S. Air Force Office of Scientific Research Mach 6 Quiet Tunnel. The freestream perturbation convected downstream in the wind tunnel to interact with a flared cone model. The model is a body of revolution bounded by a circular arc with a 3.0 m radius. Two different nose tips were used in this experiment: a 1.0 mm nose tip and a 0.16 mm nose tip. Fourteen fast pressure transducers were used to measure a wave packet generated in the cone boundary layer by the freestream perturbation. This wave packet grew large and became nonlinear before experiencing natural transition in quiet flow. Breakdown of this wave packet occurred when the amplitude of the pressure fluctuations at the most unstable second-mode frequency was approximately 10% of the surface pressure for a nominally sharp nose tip. The amplitude of the second-mode instability at the neutral point on the flared cone is estimated to be on the order of times the surface pressure for the 1.0 mm nose tip and times the surface pressure for the 0.16 mm nose tip.

Experimental investigation of detonation quenching in non-uniform compositions

This paper presents an experimental investigation into the dynamical behavior of detonation in non-uniform mixtures of propane and oxygen at initial pressure and temperature of 200 mbar and 290 K, respectively, with gradients of initial composition parallel to the direction of detonation propagation. The experiments were carried out in a 50 × 50-mm2-square section, 665-mm-long, vertical chamber. Filling was made from the chamber top-end by means of a planar, separate injection of the mixture components. The non-uniform distributions in the chamber were then controlled by molecular diffusion with diffusion time defining the composition gradient. A Chapman–Jouguet detonation was smoothly transmitted at the chamber bottom-end from a 3.6-m-long driver tube connected to the chamber. Injection and diffusion were monitored in such a way that the mixture composition at the chamber bottom-end was the same as the uniform composition in the driver tube at ignition time. Fast pressure transducers, sooted plates, Schlieren and CH* chemiluminescence visualizations were used to characterize the longitudinal velocities and cell widths, the front structure, the propagation modes and the quenching mechanisms of detonation. Detonation dynamics was found to depend on the steepness of the composition distribution and on the local and initial values of the equivalence ratio. In particular, a sudden one-dimensional detonation quenching of the multicellular detonation was observed in a lean to leaner distribution with a large gradient, whereas a progressive quenching through marginal propagation was obtained with a small gradient and a lower local equivalence ratio. The quenching mechanisms appear to be controlled by the rates of variation of composition and of detonation characteristic lengths: the faster the rate of change, the more sudden the quenching.

Investigation of transverse jet injections in a supersonic crossflow using fast-responding pressure-sensitive paint

Traditional pressure-sensitive paint (PSP) systems can provide data with high spatial resolution; however, the bandwidth is limited to a few Hz by the response time of the paint. Fast-responding paints have demonstrated response times of up to 100 kHz. Ultra-bright LEDs and fast-framing cameras combined with a porous polymer PSP can be used to produce a system capable of both high spatial resolution and high temporal bandwidth. Measurements of mean and unsteady pressure have been acquired on an experimental setup composed of a Mach-2 channel flow with transverse jet injection. The unsteady pressure data clearly resolve structures not present in the mean pressure data, including multiple lambda shocks upstream of a strong bow shock, high-frequency perturbations in the location of these shocks, and significant deformations of the bow shock structure. Time series of data can be extracted at each pixel, and the spectral content and phase relationship of the flow can be presented as maps of pressure fluctuations at specific frequencies or as correlation coefficients between a control point and the remaining flow. This type of map can be created using arrays of fast pressure transducers; here, we present data representing an array of over 26,000 fast pressure transducers.

An investigation of microscale explosive vaporization of water on an ultrathin Pt wire

The explosive vaporization of water close to its superheat limit was investigated at the microscale level using a short (1 mm in length) and ultrathin ( 10 μm in diameter) Pt wire. It was possible to obtain novel visualizations and simultaneously pressure and temperature measurements in the vapor microregion, thus accomplishing a step forward in understanding the complex behavior of explosive vapor nucleation, growth, and subsequent collapse, despite experimental difficulties posed by the very short time and length scales of the phenomena. The temperature results verify (to the best of our knowledge, for the first time) the limit of superheat reported in the classical work of Skripov. The nucleation temperature increases with heating rate until a maximum limit is reached. The maximum heating rate was 86×10 6 K/s and a maximum nucleation temperature of 303°C could be obtained. For the visualization of the very rapid boiling process, a strobe microscopy technique was developed and employed. A clear difference in the mode (homogeneous vs. heterogeneous) of vapor nucleation between high and moderate heating rates was observed. A fast pressure transducer allowed to capture the acoustic emission from the expanding vapor volume. From these data, the pressure inside the growing vapor layer and the mechanical energy released by its rapid expansion could be estimated.

Fast hydrogen gas injection system for plasma physics experiments

A system has been developed for fast injection of hydrogen gas into a vacuum system, which can produce feedback controlled flows in the range 0.1-10 Torr l/s. The unit uses a fast pressure transducer as a flow sensor. The flow will respond to an external programming voltage whose time variation is as short as several milliseconds.