Simulation Of Transient Flow Research Articles

A Novel Approach Integrating the Method of Characteristics with Large Time-Step Scheme (MOC-LTS) for Efficient Transient Flow Simulation in Liquid Pipelines

Water hammer incidents pose a significant risk to the safety and stability of pipeline operations. Therefore, rapid and precise transient flow simulation is essential for efficiently developing scientific water hammer control strategies. Nevertheless, the prevailing transient flow simulation methods for liquid pipelines predominantly employ explicit schemes to solve transient flow control equations, necessitating adherence to the stability criterion of Courant-Friedrichs-Lewy (CFL) ≤ 1. This results in limited time step sizes, which in turn constrains computational efficiency, particularly when simulating hydraulic behavior in large-scale pipeline networks. In this paper, a novel approach integrating the method of characteristics (MOC) with a large time-step scheme (LTS) is proposed to enable rapid and accurate simulation of transient flow in liquid pipelines. The proposed approach discretizes the computational domain into contiguous control volumes, ategorizing them as either boundary or internal control volumes depending on whether they are affected by boundary conditions within a large time step. For internal control volumes, an LTS scheme based on the first-order Godunov format is employed to improve computational efficiency. For boundary control volumes, MOC is applied iteratively to accurately capture boundary dynamics until the simulated time matches that of the internal control volumes. Quantitative analysis is conducted to verify the performance of the proposed approach. The results confirm that the proposed approach outperforms the MOC in computational efficiency while maintaining minimal accuracy loss.

Numerical analysis of cavitation characteristics on front surfaces of different Pelton turbine buckets

Abstract Cavitation may occur in the runner bucket of the Pelton turbine, which could lead to cavitation erosion on the bucket surface. In this paper, three types of bucket were selected to carry out transient multiphase flow simulation at the same operating point of a model Pelton turbine. The hydraulic performance and cavitation characteristics of different buckets were analysed. The 3 bucket models were developed for Pelton turbines operating under the middle-high and the high-water head range, respectively. Results showed that the participation of cavitation model in simulation would slightly affect the working process of the bucket. The cavitation on the front surface of three buckets all happened at the beginning stage of jet inflowing the bucket, among which bucket C had the most serious cavitation on the front surface. This work showed different cavitation characteristics among various types of bucket, and the relevant result suggested comprehensive design considering cavitation characteristics should be done on the front surface of the bucket for a specific range of water head.

Hybrid virtual flow metering on arbitrary well patterns for transient multiphase prediction driven by mechanistic and data model

Virtual Flow Meters (VFMs) have garnered considerable attention due to their substantial benefits in curtailing the expenses associated with multiphase flow measurement. To overcome the constraints of current technologies, we introduce the Distributed Hybrid Virtual Flow Meter (HVFM-Fleet) method. This innovative approach leverages a data-driven model that integrates multi-scale features, significantly enhancing the accuracy of flow characteristic identification. Moreover, a mechanical model is crafted to translate arbitrary well networks into a virtual layout, thereby amplifying the system's adaptability to a variety of scenarios. The HVFM-Fleet capitalizes on distributed computing to reduce computational costs in large-scale simulations, establishing a database that surpasses a thousand multi-well cases—the most extensive in the transient multiphase flow simulation sector. Case studies integrate simulation data with actual measurement data from oil fields in the North Sea of the UK, with a detailed analysis of key elements such as individual wells, multiple wells, and flow allocation. The HVFM-Fleet has notably reduced the mean absolute percentage error and achieved a remarkable 140% improvement in performance compared to existing models. Furthermore, this research pioneers new metrics for assessing the volatility of predictions, setting a new standard in the evaluation of flow measurement reliability.

Numerical Simulation of Transient Flow and Heat Transfer in a Steel Ladle During Holding Period

Numerical Simulation of Transient Flow and Heat Transfer in a Steel Ladle During Holding Period

Optimized adhesive application

In the manufacturing industry, the process of applying adhesive to join two substrates can be challenging. It requires precise placement of adhesive so that it is distributed in the desired pattern, ensuring a strong bond between the substrates. Overfilling is a common practice to ensure that the bond is not underfilled after the substrates are pressed together. However, this approach leads to unnecessary adhesive waste and can result in additional cleaning work. To address these issues, an optimization algorithm has been developed that can compute an initial adhesive pattern to flow into any desired geometry. The algorithm is based on a transient squeeze flow simulation, which iteratively removes fluid material as it flows out of the target bond domain. For example, to obtain a square bond geometry after a parallel squeezing process, the adhesive needs to be initially applied in a star shape. However, the algorithm is highly adaptable and can be used for many desired bond geometries as shown in this paper. The results are independent of the mesh resolution and fluid flow law, thus eliminating the need for complex rheological fluid characterization. The algorithm requires only two input parameters, namely the target bond geometry and the degree of compression. This highly simplifies the adaption of the proposed optimization method for manufacturers, and their design requirements can be considered with ease. The results are reliable and consistent despite the simulation’s complexity. Overall, this new optimization methodology represents a significant advance in adhesive application technology, eliminating the need of overfilling and thus making the manufacturing process more efficient, sustainable and cost-effective.

Innovative groundwater management in industrial park: Optimization and modelling of extraction system

The research presented in this paper focuses on the optimization and modelling of an innovative groundwater extraction system and addresses the challenge of managing the increased groundwater level in Nitra Industrial Park, where the Land Rover Jaguar car manufacturer is located. The primary objective of this research was to determine the optimal pumping rate of the system, ensuring the maintenance of the groundwater level at the required elevation without depleting the surrounding water resources. To achieve this goal, a numerical groundwater modelling approach was utilized, employing the TRIWACO simulation package and the finite element method (FEM). The study involved various simulations under steady and unsteady flow conditions, using hydrological, geological and hydrogeological data, including the results of three proposed pumping tests conducted by INGEO, Ltd. Company, as well as measured groundwater level data from boreholes monitored by the Slovak Hydrometeorological Institute (SHMI). Implementing transient groundwater flow simulations considered the impact of a 1000-year flash flood wave (Q1000). This paper presents results of numerical modelling results, offering insights into maintaining the required groundwater elevation while considering key parameters and uncertainties for design purposes. Additionally, on-site optimization was performed to ensure efficient system operation and minimize associated costs. In conclusion, this research contributes to sustainable groundwater management in the Nitra Industrial Park, addressing the challenge of the increased groundwater level and providing valuable findings to optimize the extraction system’s performance.

Evaluation of the Aeroacoustic Sources of a Swirl Diffusor

The acoustic noise generated by air diffusers can have negative impacts on a productive working environment and thus is a considerable limiting factor in ventilation systems. A reliable prediction of sound sources and levels offers the potential to minimise noise emissions in the early design process of air diffusers. In this work, we investigate a commercially available swirl diffuser. For a complete coverage of all flow and acoustic phenomena, the swirl diffuser is only slightly modified and modelled with transient flow simulations. We use large-eddy simulations coupled with the perturbed convective wave equation to model the flow and the aeroacoustic behaviour. The diffuser can be operated over a wide range of volume flows. To limit the computational cost, we investigate the diffuser at three operating points (278, 414 and 549 m3/h). To validate the computed aeroacoustic behaviour we use acoustic measurements. Laser-Doppler-Anemometry measurements are carried out to validate the flow simulation. The transient model is able to predict a sound spectrum and attribute certain features of the spectrum to geometric features of the air diffuser. Furthermore, the flow structures responsible for the sound are determined. These insights can offer guidelines for future designs of comparable air diffusers.

A model for the dissipation rate in linear unsteady flow through porous media

We present a model for the volume-averaged dissipation rate in linear unsteady flow through porous media. The model is derived by blending a new small-time asymptotic expression for the dissipation rate obtained from boundary layer theory with the known large-time asymptotic expression obtained from Darcy's law. The resulting model is a second-order Volterra functional of the volume-averaged acceleration. We validate the model with an analytical solution for transient flow through a porous medium composed of circular tubes and with numerical simulations of transient and oscillatory flow through a cylinder array and through a hexagonal sphere pack.

A Comparison of Hydrogen and Gasoline Piston Ring Simulations

This paper presents a transient mixed-lubrication hydrodynamic and gas flow simulation model for a piston ring pack for a four-stroke internal combustion engine. The analyses carried out compare two fuel types, hydrogen and gasoline, at a 2000 rpm low engine load (20%), as well as 3000 rpm low (20%) and high (100%) engine loads, to investigate the effects of the different fuels and loading conditions on the ring pack. In particular, the minimum oil film thickness at the top compression ring, the total ring friction of the ring pack, the friction power loss and the blow-by are studied. The simulation shows that, under the high load conditions at 3000 rpm, the hydrogen variant exhibits larger friction power losses, around a 200 W peak difference and larger blow-by throughout the expansion stroke of the engine cycle. A similar trend can be observed for the low loads, where larger friction power losses with peak differences of 30 W and 40 W for 2000 rpm and 3000 rpm, respectively, are observed. The blow-by results for the low load at 2000 rpm show a slight increase of approximately 22% more gas flow into the crankcase, while the 3000 rpm simulation shows a 50% increase in blow-by for the hydrogen variant at low load and a 40% increase at high load. The findings that are presented indicate that, although alternative fuel sources such as hydrogen are very attractive alternatives to fossil fuels such as gasoline, there can be unwanted side effects that could lead to the permanent damage of components through quicker wear or hydrogen embrittlement from the blow-by gas.

Simplified coronary flow reserve calculations based on three-dimensional coronary reconstruction and intracoronary pressure data.

Measurements of fractional flow reserve (FFR) and/or coronary flow reserve (CFR) are widely used for hemodynamic characterization of coronary lesions. The frequent combination of the epicardial and microvascular disease may indicate a need for complex hemodynamic evaluation of coronary lesions. This study aims at validating the calculation of CFR based on a simple hemodynamic model to detailed computational fluid dynamics (CFD) analysis. Three-dimensional (3D) morphological data and pressure values from FFR measurements were used to calculate the target vessel. Nine patients with one intermediate stenosis each, measured by pressure wire, were included in this study. A correlation was found between the determined CFR from simple equations and from a steady flow simulation (r = 0.984, p < 10-5). There was a significant correlation between the CFR values calculated by transient and steady flow simulations (r = 0.94, p < 10-3). Feasibility was demonstrated of a simple hemodynamic calculation of CFR based on 3D-angiography and intracoronary pressure measurements. A simultaneous determination of both the FFR and CFR values provides the capability to diagnose microvascular dysfunction: the CFR/FFR ratio characterizes the microvascular reserve.

A hybrid thermal management system combining liquid cooling and phase change material for downhole electronics

The electronics inside the logging tools are prone to failure due to the extreme thermal environments. In this study, a hybrid thermal management system using liquid cooling and phase change material (PCM) for downhole electronics is proposed to extend the workable time. In this system, a spiral pipe and a S-shaped pipe are respectively arranged inside the PCM and the cold plates to strengthen the heat exchange. To investigate the performance of this system, the transient flow and heat transfer simulation are implemented using finite element method. The accuracy is validated by comparing with the reported experimental results, showing an error of less than 6.7 %. The results show that the hybrid thermal management system increases the operating time of the electronics from 230 min to 450 min, which is attributed to the introduction of liquid cooling. The maximum temperature difference between the electronics and PCM reduces from 30 °C to 2 °C. Moreover, the effect of flow rate, spiral pipe spacing, heating power and ambient temperature on the temperature control performance are explored. This work provides a guidance for the design and optimization of logging tools, which is significative to shorten their research and development cycle.

Numerical simulation of transient pipe flow with entrapped air and wet bed effects

In this study, the evolution of transient pipe flow along the wet bed is numerically investigated. In the investigation, the shear stress transport k-ω model is used and the volume of fluid method is employed to track the surface of air and water. Two key parameters in the flow as upstream head H and initial water depth h in the pipe are examined. It is found that the bottom stress is significantly affected by the two parameters. The upstream head H determines the magnitude of the shear force, and the downstream water depth in the pipe affects the stability of the shear force. The boundary layer separation and flow pattern are the essential causes of shear instability. By analyzing the simulation results, an empirical equation with the average flow velocity is obtained to estimate the overflow capacity of the pipe by just the upstream water level and the depth of the wet bed.

Developments in analytical wall shear stress modelling for water hammer phenomena

New developments in analytical modelling of wall shear stresses during water hammer events are presented and discussed in this paper. These include further development of models based on the quasi-steady and unsteady hypothesis of hydraulic resistances. All the analyzed solutions have been improved so that they have extended ranges of applicability and the simplest possible mathematical form. Exemplary comparative studies were carried out, which showed their advantages and disadvantages. Explicit analytical formulas of wall shear stress were derived for the first time. They will be particularly useful at the stage of design and modernization of the pressurized piping systems (water supply, oil-hydraulics etc.) and enable effective analysis of leakages and other damages (ruptures, fatigue related failures) occurring in industrial pipeline systems. With their help, it will be easier to prevent the increased pulsating pressures occurring during water hammer events (protect against failures), and to verify numerical models used for years in simulations of transient pipe flows.

Stream and Potential Functions for Transient Flow Simulations in Porous Media with Pressure-Controlled Well Systems

Gaussian solutions of the diffusion equation can be applied to visualize the flow paths in subsurface reservoirs due to the spatial advance of the pressure gradient caused by engineering interventions (vertical wells, horizontal wells) in subsurface reservoirs for the extraction of natural resources (e.g., water, oil, gas, and geothermal fluids). Having solved the temporal and spatial changes in the pressure field caused by the lowered pressure of a well’s production system, the Gaussian method is extended and applied to compute and visualize velocity magnitude contours, streamlines, and other relevant flow attributes in the vicinity of well systems that are depleting the pressure in a reservoir. We derive stream function and potential function solutions that allow instantaneous modeling of flow paths and pressure contour solutions for transient flows. Such analytical solutions for transient flows have not been derived before without time-stepping. The new closed-form solutions avoid the computational complexity of time-stepping, required when time-dependent flows are modeled by superposing steady-state solutions using complex analysis methods.

Transient modelling of water condensation rate for top of line corrosion

Top of line corrosion (TOLC) is typically a concern in the first few kilometres of wet gas pipelines where water in the warm gas condenses on the cold pipe walls. With the introduction of a subsea tieback to existing infrastructure, the changing fluid composition and temperature profiles may increase condensation in sections not previously expected to have condensation. Accurate prediction of the water condensation rate (WCR) becomes essential to support reliable corrosion modelling. Transient flow simulation of pipeline operating conditions and detailed heat transfer modelling is required to calculate the WCR. This calculation is complicated because the mass of water condensation is very small compared to the fluid mass in the pipeline, and sensitive to glycol that is often present in the aqueous phase for hydrate management purposes. This paper introduces a method to calculate WCR by using detailed transient modelling of the pipeline operating conditions. The fluid thermal hydraulic behaviour and hydraulic pressure drop in the pipeline are considered in the model. The fluid composition in the pipeline and glycol component in the aqueous phase are calculated by using a PVT software package. A few sensitivity studies will also be presented. The implications of Equation of State (EoS) and transient flow module on WCR calculation will be quantified. The WCR sensitivity results will be analysed based on varying inlet temperatures, glycol concentrations, and pipeline heat transfer coefficients. A WCR calculation method will be recommended for TOLC modelling.

Three-Dimensional Simulation of Transient Flows during the Emptying of Pipes with Entrapped Air

Three-Dimensional Simulation of Transient Flows during the Emptying of Pipes with Entrapped Air

Dynamic characteristics of a running away pump-turbine with large head variation: 1D + 3D coupled simulation

The dynamic characteristics of running away pump turbines (PTs) with a large head variable amplitude have not been understood thus far, primarily because of two difficulties in simulation and analysis. The first is how to provide accurate time-varying boundary conditions for transient simulation of the turbine runaway process (TRP). The other is how to determine the specific appearance time of each frequency component of the complex pressure fluctuations. This study presented a one- and three-dimensional (1D-3D) coupled approach considering waterway dynamics to provide accurate unsteady boundary conditions for the transient flow simulation of a PT with a large head variable amplitude. The short-time Fourier transformation (STFT) approach was adopted to analyse the time-frequency characteristics of the transient pressures and impeller forces. The study found that the fluctuations of pressures and impeller forces during the TRP of the PT with a large head variable amplitude contained two exclusive fluctuation frequency components. The former was approximately three times the rated rotational frequency of the impeller. The later was a series of integer fold transient rotational frequencies of the impeller, which was irrelevant to the rotor-stator interactions. The findings have important value for controlling the pressure fluctuations during the TRP of PTs.

Well-scale experimental and numerical modeling studies of gas bullheading using fiber-optic DAS and DTS

Bullheading is an effective well control technique to pump produced fluids back into the formation during drilling and completion operations to regain well control. However, existing bullheading procedures are often based on a trial-and-error approach due to the complexity of modeling counter-current gas flow mechanisms in well control simulators and the lack of empirical bullheading datasets in full-scale conditions. To address this gap, a 5163-ft-deep experimental wellbore was utilized to conduct bullheading tests using nitrogen and water to simulate a “gas below BOP” scenario. We present a novel application of fiber-optic distributed acoustic sensor (DAS) and distributed temperature sensor (DTS) in facilitating the measurement and monitoring of gas slugs in the wellbore for an improved understanding and modeling of the gas bullheading processes.Full scale tests were performed by injecting a nitrogen slug into the wellbore annulus which was bullheaded with water while taking returns via tubing. A detailed analysis of the bullheading data for two different gas slug volumes and bullheading rates is presented. DTS and DAS data were analyzed using a variety of time- and frequency-domain signal processing techniques to estimate displacement velocities and changing gas slug lengths during injection, subsequent expansion, and displacement in the annulus. Numerical simulations were also performed for an improved understanding of the bullheading processes using a drift flux model (DFM)-based transient multiphase flow simulator modified for counter-current flow situations. Different gas slip models, used in the DFM, were benchmarked for the best match with the DAS and DTS measurements obtained from the bullheading experiments. The data from downhole pressure gauges were also compared to the DAS and DTS measurements as well as the results from numerical simulations and satisfactory agreements was obtained.This study demonstrates a novel application of DAS and DTS in obtaining high-resolution spatial-temporal measurements for the facilitation of improved understanding and modeling of well-scale bullheading hydrodynamic behaviors. The evaluation, selection, and calibration of transient multiphase flow sub-models used in this study improved the understanding of the counter-current flow in a well and provided references for applying the DFM in simulating bullheading operations.

Mixing in Low Reynolds Number Reacting Impinging Jets in Crossflow

AbstractPrevious efforts to model uranyl fluoride formation in an impinging jet gas reactor underpredicted spatial mixing and overpredicted chemical conversion into particulates. The previous fluid dynamics model was based on the solution of the Reynolds Averaged Navier Stokes equations. After simulating fluid dynamics, aerosol dynamics were superimposed onto CFD-simulated gas reactant species concentrations. The current work explores the influence of complex unsteady flow features on the overall flow physics and chemistry for a low Reynolds number, opposed flow, impinging jet gas reactor where there is a low Reynolds number cross flow. The objective of this study was to assess the impact of model formulation on scalar mixing and transport. Transient flow simulations were performed using Scale Resolving Simulations. Large-Eddy Simulations with the dynamic Smagorinsky turbulence model were performed along with simulations which directly resolved the flow. Average and root-mean-square (RMS) velocities and species concentrations were computed along with modeled and resolved turbulence kinetic energy (TKE), modeled turbulence dissipation, and modeled turbulent viscosity. Lagrangian flow tracers were also used to quantify species concentrations along path lines emanating from the jet tips. Transient simulation data were compared to results from RANS simulations using the k-ω shear stress transport (SST) model and Reynolds Stress Model (RSM). Transient simulations showed spatial mixing patterns which were more consistent with experimental data and helped elucidate the process of particle formation observed in experiments.

On the Self-Similarity in an Annular Isolator under Rotating Feedback Pressure Perturbations

In this paper, the transient flow simulation in an annular isolator under rotating feedback pressure perturbations simplified from the rotating denotation wave (RDW) is performed. The instantaneous flow characteristics and the self-similarity of the isolator flow-field are investigated in detail. It is found that a helical moving shock wave (MSW) and a quasi-toroidal terminal shock wave (TSW) are induced in the isolator. Hence, the flow-fields on the meridian planes could be classified into three zones, i.e., the undisturbed zone, the terminal shock wave/moving shock wave/boundary layer interaction (TSW/MSW/BLI) zone and the moving shock wave/boundary layer interaction (MSW/BLI) zone. The TSW/MSW/BLI zone is characterized by the coupling of the TSW/BLI and the MSW/BLI due to their small axial distance, which intensifies the adverse pressure gradient on the meridian planes, thus rolling up large separation bubbles developing along the MSW driven by the circular pressure gradient. In the MSW/BLI zone, the shock induces the boundary layer to separate, forming a helical vortex located at the foot of the MSW. During the upstream propagation process, the pattern of the MSWs transforms from a moving normal shock wave to a moving oblique shock wave with decreased strength. Moreover, after the collision with the MSWs, P, Temp and S of the flow elevate with the prompt decrease of va, while vθ increases to a higher level. Despite the deflection effect of the MSWs on the streamlines, the flow direction of the air still maintains an almost axial position at the exit, except in the adjacent region of the MSW. Likewise, three types of zones can be determined in the flow pattern at the exit: the rotating detonation wave/boundary layer interaction (RDW/BLI) zone, the expansion zone, and the vortices discharge zone. Comparing the transient flow patterns at different moments in one cycle and between adjacent cycles, an interesting discovery is that the self-similarity property is observed in the flow-field of the annular isolator under rotating feedback pressure perturbations. The global flow structure of the isolator at different moments shows good agreement despite its rotation with the RDW, and the surface pressure profiles of the corresponding meridian planes all match perfectly. Such a characteristic indicates that the rotation angular velocity of the TSW and the MSW are equal and hold invariant, and the isolator flow could be regarded as a quasi-steady flow. On this basis, the theoretical model of the inclination angles of the MSW by the coordinate transformation and velocity decomposition is developed and validated. The relative errors of the inclination angles between the predicted and measured results are below 3%, which offers a rapid method to predict the shape of the MSW, along with a perspective to better understand the physical meaning of the shape of the MSW.