Transient Pressure Fluctuations Research Articles

Effect of fracturing on transient pressure fluctuation of tubing in ultra-deep well

The tubing is prone to failure during the fracturing process because of the high pressure and massive flow of the fracturing fluid. The fast change in pressure and velocity inside the tubing caused by an instantaneous shift in the flow boundary of the fracturing fluid can lead to tubing failure or possibly fracture, which poses a major risk to the integrity of the wellbore. In the process of high pump pressure and large displacement fracturing in ultra-deep wells, the calculation model of fluid hammer in the fracturing string is constructed in this article in accordance with the instantaneous pump stop condition. The quasi-dynamic boundary conditions of fracturing fluid are also considered. It is discovered how wellhead pressure is affected by pump stop time and fracturing fluid displacement. In this paper, the model is verified based on the field fracturing data of an ultra-deep well and the error between the calculated value and the field value is 1.04%. The simulation results show that the wellhead pressure declines once the pump is turned off, fluctuates close to the equilibrium pressure value, and the magnitude of the fluctuation steadily shrinks until it reaches the equilibrium pressure. The difference between the peak pressure and the stable value is within 5 MPa, and the difference is 2.61 MPa under the fracturing condition of the example well in this paper. The shorter the pump shutdown time, the earlier the inflection point appears, and the greater the pressure mutation value. In the five groups of pump stop time set in this paper, when the stop time is 2.5 s, the peak pressure can reach 80.35 MPa, which is 24.77 MPa higher than the peak pressure when the pump stops for 12.5 s. Proppant content combined with appropriate wellhead pump pressure can reduce the wellhead pump stop pressure under the premise of supporting the formation fracture is not closed. In addition, when the proppant content in the fracturing fluid is high, the additional axial force on the tubing is large and the fluctuation is advanced.

Research on gas–liquid two-phase transient process of reactor coolant pump under stuck shaft accident

The stuck shaft accident (SSA) is a typical and severe accident of the reactor coolant pump (RCP). During this accident, significant friction and heat generation result in gas–liquid two-phase flow, which adversely affects the working performance and stability of the RCP. In order to explore the internal flow field and transient pressure fluctuation of the two-phase flow in the RCP under the SSA, this study adopts three methods of standard k-ε, Large Eddy Simulation (LES) and Lattice Boltzmann Method-Large Eddy Simulation (LBM-LES) for refined simulation and then are validated by experiments. It finds that the gas volume fraction (GVF) is relatively high in the inlet path of the guide vane during the initial stage, and then the gas disperses from the suction surface of the impeller blade to the pressure surface. When the GVF increases, the small gas masses accumulate into large masses and collapses in the RCP. At this time, the vorticity in the impeller path increases and then decreases at the outlet. The pressure fluctuation on the pressure surface at the impeller outlet increases with the increase of GVF. The impact of the GVF on the pressure surface is greater than that on the suction surface, particularly in the high-frequency band during the initial stages of the SSA. Among these three models, LBM-LES demonstrates the highest accuracy with a maximum deviation of only 8.84% when the inlet GVF is 10%. The research results improve the prevention and mitigation ability of related accidents, and provide theoretical basis and technical support for subsequent optimization and improvement.

The influence of high-speed train’s transient pressure change on the fetal growth of SD rats

ABSTRACT This research aims to explore the influence of transient pressure fluctuation inside high-speed trains passing throught tunnels on the fetal growth of Sprague – Dawley (SD) rats. A pressure variation simulation system was designed and exposure experiments were performed on SD rats. Forty-eight SD rats are divided into two control groups and two experimental groups, and are then exposed to transient pressure alternation (−1200 Pa ~1200 Pa) from gestation day 0 to gestation day 5 (GD 0–5). Fetal growth and development indicators on GD12 and GD18 between experimental and control groups were compared. Statistical results showed that, compared to the control group, the key indicators in the experimental group, including placental weight, placental diameter, fetal weight, and crown-to-rump length have decreased by 4.77%, 3.38%, 6.20%, and 3.75% respectively on GD18. The findings imply that the pressure fluctuation environment of high-speed trains has potential effects on the fetal growth of SD rats.

On the effect of an ANC system towards the transient pressure fluctuations caused by smart-grid controlled centrifugal pumps

Smart-grid control aims to use current power converter technology of pump drives for grid stabilization. Hereby, fluctuations of the power grid frequency are transmitted to the pump drive resulting in pump speed changes. Along with the inherent impeller design these pump speed changes are resulting in pressure pulsations which propagate as hydro acoustic pressure waves throughout the pump system causing noise and vibration issues in the piping system. Therefor, in order to realize smart-grid control, a solution must be found to attenuate or counteract these hydro acoustic pressure waves. In an earlier work [1], an active noise control (ANC) system to reduce pressure pulsations at a pump’s blade passing frequency (BPF) was published with the focus on constant points of operation. However, utilizing smart-grid control will results in high gradients of the pump speed and constantly changing points of operation are to be expected. This paper aims to attack those kinds of operating conditions. Within this paper, moving frequencies of interest at different pump speed gradient with and without active attenuation are analyzed and extracted from time series data by means of Vold-Kalman order tracking filter. In relation to possible fluctuations in the power grids frequency, the active attenuation performance of the ANC system is evaluated.

A Method for Predicting the Aeroelastic Response of Radial Turbomachines

AbstractAircraft intermittent combustion engines often incorporate turbochargers adapted from ground-based applications to improve their efficiency and performance. These turbochargers can operate at off-design conditions and experience blade failures brought on by aerodynamic-induced blade resonances. A reduced-order model of the aeroelastic response of general fluid–structural configurations is developed using the Euler–Lagrange equation informed by numerical data from uncoupled computational fluid dynamic (CFD) and computational structural dynamic calculations. The structural response is derived from a method of assumed-modes approach. The unsteady fluid response is described by a modified version of piston theory that approximates the local transient pressure fluctuation in conjunction with steady CFD solution data. The reduced-order model is first applied to a classical panel flutter scenario and found to predict a flutter boundary that compares favorably to the boundary identified by existing theory and experimental data. The model is then applied to the high-pressure turbine of a dual-stage turbocharger. The model predictions are shown to reliably determine the lack of turbine blade flutter and rudimentary damping comparisons are performed to assess the ability of the model to ascertain the susceptibility of the turbine to forced response. Obstacles associated with the current experimental state of the art that impinge upon further numerical validation are discussed.

Influence of asymmetric inflow on the transient pressure fluctuation characteristics of a vertical mixed-flow pump

In order to investigate the influence of asymmetric inflow on the internal flow fields of a vertical mixed-flow pump, numerical simulation of unsteady flow was carried out under four inflow angles ( θ = 0°, 10°, 20°, and 30°). The reliability of the calculation results was validated through an external characteristic experiment. The fluctuation value of the pressure was defined to obtain the transient pressure fluctuation intensity distribution. Three monitoring points were arranged to compare pressure fluctuation characteristics under different inflow angles. The results suggested that the increase in the inflow angle caused the design operation points to deviate to the over-load flow rate. When the inflow angle increased from 0° to 30°, the axial velocity distribution coefficient and weighted average angle at the inflow runner outlet both decreased. The overall transient pressure fluctuation intensity inside the impeller increased, especially on the pressure side of the blade. Additionally, the transient pressure fluctuation intensity on the pressure side of the guide vane also increased significantly. As a result, the amplitude of pressure fluctuation at the dominant frequency of each monitoring point increased. Relatively speaking, the negative influence of asymmetric inflow on the operational stability of the pumping station was further extended under the part-load flow rate.

Prediction of Transient Pressure Fluctuations within a Low-Pressure Turbine Cascade Using a Lanczos-Filtered Harmonic Balance Method

Unsteady pressure fluctuations measured by fast-response pressure transducers mounted in a low-pressure turbine cascade are compared to unsteady simulation results. Three differing simulation approaches are considered, one time-integration method and two harmonic balance methods either resolving or averaging the time-dependent components within the turbulence model. The observations are used to evaluate the capability of the harmonic balance solver to predict the transient pressure fluctuations acting on the investigated stator surface. Wakes of an upstream rotor are generated by moving cylindrical bars at a prescribed rotational speed that refers to a frequency of f∼500 Hz. The excitation at the rear part of the suction side is essentially driven by the presence of a separation bubble and is therefore highly dependent on the unsteady behavior of turbulence. In order to increase the stability of the investigated harmonic balance solver, a developed Lanczos-type filter method is applied if the turbulence model is considered in an unsteady fashion.

Research on the influence of production fluctuation of high-production gas well on service security of tubing string

The production of high temperature and high pressure gas wells fluctuates with time, which makes the pressure in the string fluctuate obviously and affects the service security of tubing string. In this paper, a pressure fluctuation model of the complete production process (including well opening, production and shut-in) is established, which is suitable for the multiphase flow of gas well. The pressure fluctuation in the tubing string is simulated. Influence of different well depth and average production on the fluctuating pressure of gas well are analyzed. According to the research results, if the well opening time top is 50 s, a transient pressure fluctuation is generated at wellhead and drops gradually. After the production starts, a pressure fluctuation will occur at wellhead 10~15 s after top, which is small and attenuates quickly. Pressure increases quickly in the shut-in moment and reaches the peak at tsh. Although pressure increases gradually with the well depth, fluctuation flattens out. The hysteresis phenomenon in appearance of pressure wave becomes more and more obvious with the well depth. The greater the production of gas well, the greater the pressure fluctuation in tubing string during well opening and production, but the value may not be very high. During well shut-in, the greater the production, the greater the pressure fluctuation and the value. Amplitude, angular frequency and value of phase are in direct proportion to pressure fluctuation degree and valve radix is in inverse proportion to pressure, which means that the greater the valve radix, the smaller the pressure.

Experimental shell-side surface pressure measurements on tubes within a model helical coil heat exchanger

The tube and shell Helical Coil Heat Exchanger (HCHX) geometry, also known in multiple industries as the Coil-wound (CWHE), and Spiral-wound heat exchanger (SWHE), has recently been under greater investigation due to the interest in cryogenic, solar, and nuclear industry applications. Helical Coil Steam Generators (HCSGs) have adjacent tube bundles that coil in opposite directions at different helical pitches. While this design is known to increase heat transfer and provide a higher volumetric efficiency, few studies look at the changes the coiling arrangement has on forces acting on the tube. This study investigates the pressure on the surface of the tubes in this complex type of cross-section arrangement as compared to standard tube bundle arrangements. Experiments were conducted at Reynolds Numbers 8500 and 11,700 based on tube diameter and free-stream velocity. Pressure Sensitive Paint (PSP) was used on the shell-side surface of the tubes along with dynamic pressure sensors to visualize tube surface pressure and measure pressure fluctuations. Instantaneous pressure analysis using PSP and dynamic pressure transducers showed agreement with peaks of transient pressure fluctuations at approximately 9.8, 19.7 and 27.5 Hz. Previous studies have grouped tube surface pressure based on geometric parameters such as lateral pitch ratio, while the analysis of the pressure fields from this geometry showed pressure profiles unique to individual planes regardless of equivalent lateral pitch ratio.

Experimental study on the particle flow patterns in a cyclone dipleg with a trickle valve

An experimental apparatus including a dipleg and a trickle valve was established to simulate the operation of a suspended dipleg-trickle valve system of cyclone used in fluid catalytic cracking (FCC) unit. The flow regimes in the dipleg and the discharge modes in the trickle valve were studied by combining the observation of experimental phenomena with the analysis of transient pressure fluctuation. The results show that the flow regimes in the dipleg have two types—the dilute–dense phase coexisting falling flow and the dilute falling flow. Correspondingly, the trickle valve also has two discharge modes—the intermittent periodic dumping discharge and the continuous trickling discharge. The power spectrum density of pressure fluctuation displays that the gas–solids flow in the dipleg-trickle valve system is characterized by a low-frequency pulsation. The coherence coefficient explains the origin and propagation of pressure fluctuation in the system. Eventually, a map describing the flow regimes and discharge modes related to the operation parameters was proposed, which can provide a helpful guidance for the operation of cyclone dipleg-trickle valve system in FCC unit.

Analysis of Transient Pressure Source Characteristics of Trim Balance Pipeline System

Based on the hydraulic calculation of AMEsim software, adjust the pipeline and working conditions of the trim balance system, and explore the influence of water transfer pressure, pipeline length and valve closing time on the transient pressure fluctuation during the working process, and obtain the pressure change law and corresponding Relationship, according to the analysis gives preliminary optimization suggestions, sums up the scheme and scope of reducing water transfer pressure, shortening pipeline length, extending valve closing time, providing reference for optimizing system design and control, and proposing control from noise source level The method of transient noise caused by water hammer phenomenon provides an idea for controlling the transient noise of pressurized pipelines of ships and underwater vehicles.

Effect of trailing-edge serrations on noise reduction in a coupled bionic aerofoil inspired by barn owls

Noise reduction is an important development direction for aircrafts and wind turbines. Owl wings have three unique morphological characteristics (leading-edge serrations, trailing-edge serrations and velvet-like surfaces) that effectively suppress aerodynamic noise in low Reynolds numbers. Among them, trailing-edge serrations are widely considered the most effective noise-reduction method. Although different serrations have been studied, the quantitative relationship and influence mechanism between the serration shape, wavelength and amplitude are poorly understood. The acoustic characteristics of asymmetrical aerofoils with different trailing-edge serrations have not been fully studied. This work investigates the flow characteristics and acoustic scattering mechanisms of novel owl-based aerofoils with different trailing-edge serrations. A sensitivity analysis is utilized to quantitatively investigate the influence and interaction mechanisms of the shape, wavelength and amplitude in trailing-edge noise reduction. Numerical simulations of the transient flow over the aerofoil are performed via the large eddy simulation method, and the acoustic far-field is obtained by solving the Ffowcs Williams and Hawkings equation. The results indicate that the sawtooth and sinusoidal serrations provide the most significant noise reduction effects; the maximum noise reduction is 8.74 dB. The wavelength and amplitude play similar roles, but the amplitude has relatively greater influence. For the sawtooth and sinusoidal serrations, the large-scale vortex structures are broken into many small-scale spiral vortex structures due to the presence of the sharp serration tip. The serrations can effectively reduce the coherence of the turbulent fluctuations due to spanwise variations in the edge and may be the main reason for noise suppression. The original owl-based aerofoil generates more low-frequency noise and less high-frequency noise than aerofoils with trailing-edge serrations. The peak noise frequencies of all aerofoils are approximately 400 Hz; hence, low-frequency noise is a dominant influence in noise generation. Furthermore, the acoustic sources generated by transient pressure fluctuations are mainly located on the serration root.

On the Prediction of Pressure Fluctuations and Pressure Drop Caused by Confined Bubble Growth During Flow Boiling in a Rectangular Mini/Micro-Channel

Heat-sinks based on flow boiling in microchannels have the potential to mitigate temperature rise in high heat flux devices such as electronic equipment. One of the major challenges is the instability associated with pressure fluctuations caused due to the confined bubble growth during boiling in a microchannel. This paper presents a comprehensive model to estimate the dynamic pressure fluctuations in a channel of rectangular cross-section and compares with the experimental results. The time-averaged pressure drop obtained from the transient model has been verified with the experimental results and the steady two-phase flow pressure drop correlations. Effects of various parameters such as heat flux and mass flux on the time-averaged pressure drop and the transient pressure fluctuations are presented. The paper also provides an approximate methodology to estimate the nucleation frequency derived from the waiting period of the bubble. The calculated frequency is validated qualitatively with the experimental observation available in the literature. The current work also demonstrates that the transient pressure drop models, which, with suitable inputs, predict the local pressure fluctuations during confined bubble growth, can also be used to predict the steady- flow pressure drop.

Transient Pressure Fluctuation Effect During Gas Drilling in Horizontal Well

Combining gas drilling technology with horizontal well drilling leads to improvement in production in oil and gas reservoirs. However, wellbore gas encountering high-pressure formation gas could bring substantial risks in gas drilling process. A theoretical model for pressure wave speed and attenuation coefficient in gaseous phase flow is established and analytically solved by classic fluid-mechanics model and small perturbation theory. The simulation results suggest that the main factors affecting the pressure wave are angular frequency, pipe diameter, and original pressure. In addition, a pressure wave test device is designed to validate the model, and the experimental results fit well with the simulation results. The work presented in this paper can provide a theoretical basis for horizontal section gas drilling and can also detect gas influx to ensure safety and prevent accidents.

Aerodynamic Analyses on the Steady and Unsteady Loading-Noise Sources of Drone Propellers

This study investigated the small drone propeller noise, particularly the discrete blade passing frequency (BPF) tone and its harmonics at low frequencies less than 1000 Hz. The unsteady Reynolds-averaged Navier–Stokes equations were solved to investigate the steady and unsteady loading noise sources around the blades with a radius of 17 cm rotating at 5000 rpm (a blade tip Mach number is 0.264). The uRANS computations showed eccentric ellipsoidal isobaric surfaces on the upper and lower blade surfaces identified as a steady loading noise source of the drone propeller. A simple mathematical model of an ellipsoidal steady loading noise with the lattice Boltzmann method predicted the BPF tone and even-number harmonics comparable to NASA’s SPL measurement of two different APC 1147 SF and DJI 9443 CF drone propellers. The decaying rate of $$- 6$$ in the SPL spectrum was quite closely matched for the first two discrete tones. The transient pressure fluctuation characteristics on the upper surface of the rotating blades revealed that the unsteady loading noise by blade–vortex interactions is found most closely related to the third and sixth harmonics of the round per second noise. An unexpected fifth component also arose in some other rotational speeds because of the random nature of the phase difference of pressure fluctuations, even at the same positions of the two propeller blades.

Water Hammer in a Horizontal Rectangular Conduit Containing Air-Water Two-Phase Slug Flow

AbstractThe study of water hammer in air-water, two-phase flows in hydraulic structures such as pressurized pipelines and tunnels, siphons, culverts, and junctions is of great importance for design purposes. Water hammer if combined with a periodic slug flow would lead to severe periodic transient pressure fluctuations inside the conduit. Laboratory experiments have been conducted to investigate water-hammer pressure inside a horizontal rectangular conduit carrying a two-phase, air-water slug flow. Tests were performed in an experimental apparatus comprising a 6.8-m-long transparent pipeline 0.06 m wide and 0.1 m high. By rapidly closing a control gate at the end of the conduit, propagating pressure surges were generated. Transient pressure fluctuations were recorded by means of pressure transducers. Furthermore, a digital camera was used to document flow properties and air-bubble characteristics throughout the pipeline. Pressure measurements along the pipe indicated that two scenarios could be considered...

Cardiovascular design in fin whales: high-stiffness arteries protect against adverse pressure gradients at depth

Fin whales have an incompliant aorta, which, we hypothesize, represents an adaptation to large, depth-induced variations in arterial transmural pressures. We hypothesize these variations arise from a limited ability of tissues to respond to rapid changes in ambient ocean pressures during a dive. We tested this hypothesis by measuring arterial mechanics experimentally and modelling arterial transmural pressures mathematically. The mechanical properties of mammalian arteries reflect the physiological loads they experience, so we examined a wide range of fin whale arteries. All arteries had abundant adventitial collagen that was usually recruited at very low stretches and inflation pressures (2-3 kPa), making arterial diameter largely independent of transmural pressure. Arteries withstood significant negative transmural pressures (-7 to -50 kPa) before collapsing. Collapse was resisted by recruitment of adventitial collagen at very low stretches. These findings are compatible with the hypothesis of depth-induced variation of arterial transmural pressure. Because transmural pressures depend on thoracic pressures, we modelled the thorax of a diving fin whale to assess the likelihood of significant variation in transmural pressures. The model predicted that deformation of the thorax body wall and diaphragm could not always equalize thoracic and ambient pressures because of asymmetrical conditions on dive descent and ascent. Redistribution of blood could partially compensate for asymmetrical conditions, but inertial and viscoelastic lag necessarily limits tissue response rates. Without pressure equilibrium, particularly when ambient pressures change rapidly, internal pressure gradients will develop and expose arteries to transient pressure fluctuations, but with minimal hemodynamic consequence due to their low compliance.

Water suppliers and plumbers share backflow prevention responsibility

A goal of the water supply industry is to provide safe drinking water that meets the minimum standards established by the US Environmental Protection Agency. Utilities have invested millions of dollars in treatment processes to meet these regulations, but their investment can be swiftly negated by something as basic as transient pressure fluctuations, which allow a return flow of a contaminant or pollutant into the distribution system. Utility professionals are typically not aware of plumbing system operation details. Water suppliers need to work closely with plumbing inspectors and licensed contractors to attain cross‐connection control through plumbing code compliance. A partnership with the plumbing industry, that includes code compliance, is essential when providing safe drinking water.

Phase change phenomena in silicon microchannels

Understanding the boiling process and two-phase flow behavior in microchannels is the key to developing microchannel heat sinks for high-power microprocessors. We conducted experiments in micromachined silicon channels with a range of 27–171 μm hydraulic diameters and varying surface roughnesses. Bubble nucleation, flow patterns, wall temperature, as well as transient pressure fluctuations were recorded and analyzed. We observed both typical nucleate boiling and eruption boiling with large amounts of wall superheat in these channels, and recorded up to 138 kPa transient pressure fluctuations due to bubble nucleation. We found the boiling mechanism is strongly dependent on the wall surface roughness, and we explained the boiling mechanism in sub-150 μm diameter channels with Hsu’s model.

Harsh environment windscreen analysis and design

This paper presents the analysis and design for a multimicrophone probe placed outdoors in relatively harsh environments including high temperature, high humidity, rain, wind, and soil particles. The windscreen was designed to minimize the insertion loss as well as maintain the phase relationship in a circular 5-probe microphone array. A numerical CFD model, which accounts for wind, soil particles, the windscreen material, and transient pressure fluctuations, will be presented. The parametric design using this numerical model will be presented and discussed, along with experimental results. The experimental testing consists of measuring the wind attenuation, the insertion loss, as well as any errors in the phase relationship. Testing is done in an anechoic chamber using two methods: a stationary microphone array, and attaching the microphone system to a rotating arm to simulate the wind. Measurement results which correlate the density and thickness of the foam with the insertion loss and the drop in wind noise level caused by the foam will be presented. Also, the insertion loss due to different weather-proof coverings is reported.