Analysis Of Transient Flow Research Articles

Numerical Evaluation and High-Speed Rotating Test on Circular Arc Spring Dampers for Centrifugal Compressors

Abstract A circular arc spring damper (CASD) is a recently proposed fluid-film damper that has two or more arc-shaped centering springs and dual radial clearances formed by wire electric discharge machining (WEDM). CASD requires less space and weight than a conventional cage-centered squeeze-film damper (SFD). It provides linear stiffness and stable damping force in rotor-bearing systems to attenuate vibration due to imbalance or to improve rotordynamic stability. The authors have been investigated the dynamic characteristics of CASD in component-level experiments. However, their performance and applicability to real machines have not been confirmed in system-level experiments. Additionally, a theoretical means of evaluation for CASD should be established to predict its dynamic coefficients and to understand the mechanism of dynamic force generation. In the first part of this study, a numerical evaluation method using two-way fluid–structure interaction (FSI) analysis and its theoretical background is presented. Transient structural analysis and fluid-film flow analysis with a simple homogeneous cavitation model are coupled in the commercial multiphysics platform ansys. The accuracy of the method was validated by comparing the damping and added-mass coefficients with results from previous experiments. Furthermore, several aspects of the force generation mechanism and the difference from conventional SFD were studied numerically. The second part of the study addresses the application of CASD in a multistage centrifugal compressor. A combined 4-in. diameter, five-pad tilting pad journal bearing (TPJB) with four-arc type CASD was newly designed and manufactured. To prove the applicability of the developed damper bearing, a series of rotating tests were conducted at a high-speed balancing facility with a full-scale dummy rotor with a critical speed ratio (CSR) of approximately 3.1. The measured unbalance response showed a much lower amplification factor (AF) than that of the conventional TPJB without the damper, which infers a significant improvement in the stability. The measured responses agreed with the rotordynamic analysis, which uses the dynamic coefficients of CASD derived from the proposed numerical evaluation method.

Numerical Modelling Of Flood Induced Seepage Under Levees

Flood creates the most complex problems of engineering hydrology and extreme flood contains the crucial risk for urban areas, infrastructure, industry and agriculture. The aim of this paper is to study the transient flow caused by flood for levee of Filyos River. Numerical modeling based on finite element method was performed in the analyses. PlaxFlow which is an add-on module to Plaxis 2D, is used for the time variation of seepage in several points of interest within the levee. Exit velocity at several points of interest within the levee and degree of saturation of levee and hydraulic gradient were investigated. In addition, under seepage of water through different soil types underneath Filyos levee was examined. The results of transient flow analyses when piping occurred and sand boil formed were presented for different soil types.

Flow and structural analysis of sedimentary rocks by core flooding and nuclear magnetic resonance: A review.

Fluid flow analyses and investigations of associated structural variations in rock formations are important due to the complex nature of rocks and the high heterogeneity that exists within fluid-rock systems. Variations in fluid-rock parameters need to be ascertained over time with continuous or cyclic fluid injection into subsurface rocks for enhanced oil recovery and other subsurface applications. This Review introduces the use of the core flooding-nuclear magnetic resonance (NMR) technique for analysis of combined fluid flow and structural features in subsurface fluid-rock systems. It presents a summary of the results realized by various researchers in this area of study. The influence of several conditions, such as geochemical interactions, wettability, inherent heterogeneities in fluid flow and rock properties, and variations in these parameters, is analyzed. We investigate NMR measurements for both single fluid phase saturation and multiphase saturation. Additionally, the processes for identifying and distinguishing different fluid phases are emphasized in this study. Furthermore, capillary pressure and its influence on fluid-rock parameters are also discussed. Although this study emphasizes subsurface rocks and enhanced oil recovery, the experimental combination is also extended to core flooding using several other injection fluids and porous media. Finally, research gaps pertaining to core flooding-NMR systems regarding fluid flow, structural changes, fluid-rock systems, and instrumentation are pointed out. Transient flow analysis involving structural variations is suggested for future work in this regard.

Analysis of Transient Natural Convective Flow of a Nanofluid in a Vertical Tube

An analysis into the transient natural convective flow of a nanofluid in a vertical tube is made. The governing equations of momentum, heat transfer and nanoparticle volume fraction are deduced, and the influence of the thermophoresis parameter and Brownian motion is incorporated. By direct integration and variation of the parameter, analytical solutions are obtained for flow formation and heat/mass transfer at steady-state. On the other hand, due to the complexity of same problem at transient state, a numerical solution is used to solve the discretized equations of motion using the implicit finite difference technique. The influence of the thermophoresis parameter and Brownian motion is noted and well discussed. For accuracy check, a numerical comparison is made between the steady state and transient state solution at large time; this comparison gives an excellent agreement. The role of various principal parameters on velocity profile, temperature, concentration of nanoparticles, Sherwood and Nusselt numbers are presented graphically and well discussed. It is noted that the buoyancy ratio decreases the fluid velocity significantly.

자동차 브레이크 미세입자 포집을 위한 소형 사이클론에 관한 연구

There has been an increasing interest in the collection of fine dust generated by vehicle brakes ever since the significant decrease in emissions from the exhaust system. Herein, we investigated the effective collection of brake fine dust by applying a mini-cyclone. Numerical analyses of steady and unsteady flows for a rotating disk were performed. When the disk rotation speed was 1000 rpm, the brake cooling air exited the cooling passage at approximately 20 m/s and air flow entered the cyclone inlet at approximately 7 m/s. At this inlet velocity, the vortex flow in the cyclone was well developed, thereby indicating the potential of efficient particle collection. Numerical analysis of transient particle flows for a mini-cyclone was performed to determine the particle collection efficiency. Results indicated that the particle collection efficiency exceeded 90% for particle diameters exceeding 3 μm. Therefore, the mini-cyclone can be effectively used for collecting brake fine dust.

Investigating the Effect of Valve Shape on Anti-Lock Braking System Plunger Pump Performance Using Fluid-Structure Interaction Simulation

An anti-lock braking system (ABS) is an anti-skid braking system commonly used as a safety feature in vehicles. The hydraulic control unit for the ABS of a vehicle includes a plunger pump between the wheel and master cylinder. This paper presents numerical investigations of the effect of valve shapes on the performance improvement provided by a plunger pump, focusing on two different valve shapes, ball-type and hat-type. Transient laminar flow analyses of plunger pumps with ball and hat-type inlet valves are performed under motor speeds from 1000 to 5000 rpm using the fluid-structure interaction (FSI) and user-defined function (UDF) techniques. An experimental verification of the simulation results for the plunger pump with a ball-type valve was conducted using the standard pump test of the Mando Corporation, South Korea. A comparison of the simulation and experimental results suggests that these are in good agreement. The simulation results indicate that the hat-type valve outperforms the ball-type valve due to a shorter delay in the closing time at the end of the suction cycle. These findings suggest that valve shape has a considerable impact on the performance improvement provided by a plunger pump, providing crucial insights into the future design of high-efficiency pumps.

Coupling Simulation Model of Transient Flow in Tubing and Unsteady Seepage in Reservoir During Hydraulic Fracturing with Unstable Injection

The current research on hydraulic fracturing with unstable injection mainly focuses on laboratory experiments or field tests. However, due to the difference in scale, some conclusions derived from laboratory experiments are not suitable for field applications. Besides, there is little research on coupling analysis of transient flow in tubing and seepage in reservoir during fracturing. In this paper, the transient dynamic model of fluid in tubing and the model of unsteady seepage in reservoir were established, respectively. Furthermore, the simulation model was established by parameters coupling, which took into account the influence of reservoir breakdown on permeability. The variation of fluid pressure in the tubing of different scale was analyzed during unstable injection. Simultaneously, the amplitude frequency characteristics of fluid in the tubing were also compared between laboratory scale and field scale. The results show that the simulation model can be used to calculate the fluid pressure variation in the whole process of hydraulic fracturing. And the simulation results are basically consistent with the experimental results. The scale difference has a significant impact on the variation of fluid pressure in tubing. To improve the fluctuation amplitude of outlet pressure, it is necessary to design the frequency according to the amplitude frequency characteristics of the corresponding scale model. It can also be achieved by reducing the resistance coefficient. The research can provide guidance for parameters design in field applications. It is conducive to understand the difference between laboratory experiments and field applications.

Numerical investigation of wing–wing interaction and its effect on the aerodynamic force of a hovering dragonfly

The present research focuses on the timing of wing–wing interaction that benefits the aerodynamic force of a dragonfly in hovering flight at Reynolds number 1350. A 3-D numerical simulation method, called the system coupling, was utilised by implementing a two-way coupling between the transient structural and flow analysis. We further explore the aerodynamic forces produced at different phase angles on the forewing and hindwing during the hovering flight condition of a dragonfly. A pair of dragonfly wings is simulated to obtain the force generated during flapping at a 60° inclination stroke plane angle with respect to the horizontal. The hovering flight is simulated by varying the phase angle and the inter-distance between the two wings. We observe a significant enhancement in the lift (16%) of the hindwing when it flaps in-phase with the forewing and closer to the forewing, maintaining an inter-wing distance of 1.2 cm (where cm is the mean chord length). However, for the same condition, the lift of the hindwing reduces by 9% when the wings are out of phase/counterstroke flapping. These benefits and drawbacks are dependent on the timing of the interactions between the forewing and hindwing. The time of interaction of wake capture, wing–wing interaction, dipole structure and development of root vortex are examined by 2-D vorticity of the flow field and isosurface of the 3-D model dragonfly. From the isosurface, we found that the root vortex elicited at the root of the hindwing in counter-flapping creates an obstacle for the shedding of wake vortices, which results in reduction of vertical lift during the upstroke of flapping. Hence, at the supination stage, a dragonfly uses a high rotation angle for the hovering flight mode. It is observed that the system coupling method was found to be more efficient and exhibited better performance. The present numerical methodology shows a very close match to the previously reported results.

Experimental and Numerical Study of Air Vessel in Quasi-Two-Dimensional Transient Flow Analysis

Abstract An air vessel is a simple and effective device for protecting a pipeline system from abnormal pressure events. In order to design and select a suitable air vessel, analysis of the pipeline system is necessary. A quasi-2D approach can overcome some of the limitations of the conventional one-dimensional transient flow analysis method. However, only a few hydraulic components can be implemented in the quasi-2D approach. In this study, we propose a methodology for applying an air vessel in the quasi-2D model. An experimental study is performed for validating the proposed model. Although an identical approach involving an accumulator model is used to model the air vessel as in the 1D model, the quasi-2D model shows improved performance for the experimental system.

Load Flow and Transient Stability Analyses for an Integrated Solar Combined Cycle Station in Iraqi Southern by Using ETAP

Analyses of a power system are important for designing and operating phase execution monitoring and to ensure reliable grid operations by sufficient protection projects settings. In this paper, electrical model of a 340 MW integrated solar combined cycle (ISCC) located in the south of Iraq, is developed by Electrical Transient Analyzer Program (ETAP) and load flow, voltage stability and short circuit analyses are performed. Impact of power grid voltage instability on system buses of the power plant is estimated. Using load flow analysis that use Newton-Raphson algorithm, buses operating at under voltage due to power grid voltage instability are specified and their voltages are improved according to given voltage limitation that are based on buses criticality with regard to loads. On-load tap changers and reactive power compensation are used to improve steady state voltage stability. Optimal position for capacitor banks placement and number of capacitor banks are proposed by using optimal capacitor placement module of ETAP. The use of modern technology and advance planning have a big impact on reducing losses. The article shows that the lack of planning is one of the main causes of energy losses. The parameters of the module also indicate the voltage limits, bus voltage and ratings of available capacitor banks. The voltage limit is set at 95% ≤ V ≤ 110%, and it is global for all buses

Numerical and Experimental Analysis of Transient 2D Flow around Ship Spoiler.(Dept.M)

An experimental analysis and numerical computation were conducted for flow around ship spoiler mounted at the bottom of the ship and subjected to air injection The air was injected beside the spoiler and at a distance equals the spoiler length to stabilize cavities behind spoilers. This system was proposed to control the roll, pitch motion and speed of the ship, with injecting exhaust gas behind spoilers. The forces and moments acting on the ship's bottom depend on spoilers' inclination, extensions and positions relative to the ship's center of mass. To improve the understanding of the parameters affecting the flow field aroundsuch spoiler, experimental images of bubble formation are triggered and compared with the computed flow field at different spoiler inclination angle, and air injection position. Two dimensional Navier-Stokes code is used to model the two-phase flow field around a ship spoiler with the free surface simulation in Piecewise Linear Interface Construction (PLIC) method. The governing equations are discretized on a structured grid using an upwind difference scheme. For different conditions, the bubbles shape, the two-dimensional flow field around the spoiler body and the pressure variation on the wake of the spoiler body are computed, Flow field and bubble formation around the spoiler are recorded experimentally at different condition and time sequence with scientific video camera The Froude number was about 1.6 based on spoiler length. The computational and experimental results show that there is a good matching of bubble formation in the spoiler with 90', but in the condition of 45° the experimental images show that bubble filled the space between the bubble and the body of the ship. This is may be due to the two-dimension computational model consideration. So, a water layer was isolated between the bubble and the ship body. In the case of spoiler with 45° inclination angle, the flow is circulated inside the bubble. The bubble shape is longer which gives more negative pressure on larger area. The moment around the 450 spoiler fixationpoint is seven times of that around the 90° spoiler. In double injection condition beside and at a distance equal the horizontal spoiler length downstream the spoiler, the bubbles are more stable and the moment is higher by 7.9 and 17.8 times after 1.2 and 2 seconds, respectively, than that around the 90° spoiler. Thus, changing inclination spoiler angle and position relative to injection angle will give different bubble shapes which give different forces to control the roll, pitch motion and speed of the ship.

Modelling of soil-water retention curve considering the effects of existing salt solution in the pore fluid

Soil-water retention curve (SWRC) has a wide application in geoenvironmental engineering from the predication of unsaturated shear strength to transient two-phase flow and stability analyses. Although various SWRC models have been proposed to take into account some influencing factors, less attention has been given to consider the effects of pore fluid osmotic potential. Therefore, the key objective of this study is to extend van Genchten’s model so that osmotic potential is considered as an independent factor governing the SWRC behavior. The new model comprises only six variables, which can be calibrated through minimal experimental measurements. More importantly, most of the model parameters have physical meaning by correlating macroscopic volumetric behavior and general trends of SWRC to osmotic potential. The results of validation tests revealed that the new osmotic-dependent SWRC model can predict the retention data in terms of both total and matric suction for two different soils and various molar concentrations very good. The proposed modeling approach does not require any advanced mercury intrusion porosimetry (MIP) tests, yet it can deliver excellent predictions by calibrating only six parameters which are far less than those incorporated into similar models for saline water permeating through the pore structure.

Conjugate forced convection transient flow and heat transfer analysis in a hexagonal, partitioned, air filled cavity with dynamic modulator

Background– Forced convection heat transfer in a cavity is of great importance due to its strong relevance to the practical aspects. Most of the studies focus on this topic from a steady perspective. But adding a flow modulator enhances a system's thermodynamic performance and makes such a system more realistic and widens the field of application. Such studies are unsteady and often quite expensive. As a result, only a few literatures are available with very idealistic geometric configuration and boundary conditions. Methodology– Two-dimensional unsteady continuity, momentum and energy equations are used for the mathematical modeling of the problem incorporating the Boussinesq approximation. A free triangular discretization scheme is adopted to solve the moving mesh problem by formulating the Arbitrary Lagrangian Euler (ALE) finite element approach. Parameters– Numerical studies are carried out for a fixed Prandtl number (Pr = 0.71) and fixed geometry of the rotating blade while varying the other parameters i.e. Rayleigh number, Reynolds number and Biot number. This dynamic boundary problem encompasses a wide range of parameters i.e. (100 ≤ Re ≤ 103), (103 ≤Bi ≤ 104) and (104 ≤ Ra ≤ 107) to evaluate the thermodynamic behavior of the thermo-fluid system. External flow condition is taken into consideration in terms of Biot number. Effects of these parameters are visualized through streamlines, heatlines, spatially average Nusselt number evaluated on the heated surface and system effectiveness. Objective– Present computational study focuses on the transient analysis of the conjugate forced convection flow and heat transfer characteristics in a hexagonal, air filled cavity. This cavity is equipped with a floor heater of constant heat flux under the rotational influence of an adiabatic flow modulator. And the blade is placed in the central position of the cavity which is rotating in the clockwise direction. Also, the whole computational domain is composed of four different domains, one convective domain and three solid domains. The solid domains are made of brick and glass as per their practical aspects. Findings– A Fast Fourier Transform (FFT) analysis is presented to comprehend the thermo-oscillating system response. FFT plots indicate that for all of the cases the fundamental frequency of the system response conforms to the blade frequency. Moreover, present numerical results show that the heat transfer effectiveness has an inverse relationship with the Biot and Rayleigh numbers while improves significantly with the increase of Reynolds number and reaches a critical state for Recr = 650. Higher Reynolds number also attenuates the degree of power spectrum. Conclusion– To attain a higher heat transfer effectiveness the thermo – fluid system should be operated at low Rayleigh number with higher Reynolds number.

Transient flow simulation, analysis and protection of pipeline systems

This paper investigated the problems and impacts of transient flow in pipeline systems due to pump power failure. The impact of different protection devices was presented to assure surge protection for the pipeline system. A model via Bent-ley HAMMER V8.0 Edition was employed to analyse and simulate hydraulic transients in the pipeline system, and protec-tion alternatives were studied. Surge protection included using only an air vessel, using an air vessel and two surge tanks, and employing five air ves-sels and vacuum breaker. The obtained results for pressures, heads, and cavitation along the pipeline system were graph-ically presented for various operating conditions. Using five air vessels with vacuum breaker valve as surge protection proved to be more effective and economical against pump power failure. Changing the flow density did not have a significant impact on the pressures. For protection with an air vessel; it was concluded that the value 40% of the original diameter for inlet pipe diameter of air vessel, and the value of 2/3 of original pipe diameter were critical values for the transient pressures. Cast iron pipes proved to be the best pipe material for all studied volumes of the air vessel. For protection with an air vessel and two surge tanks; as the inlet pipe diameters increased the maximum pressures in-creased and the minimum pressures decreased. Regression analyses were performed obtaining equations to predict the pressures according to the inlet pipe diameter, the area of surge tank, and the pipe diameter.

Reducing Groundwater Pumping Cost Using Alternate Pulsed Pumping.

This paper deals with water pumping cost minimization, in a confined infinite aquifer, proposing an alternate pulsed pumping schedule. The transient flow analysis is conducted for two wells with equal pumping rates. Specifically, two pumping schedules are analytically compared. In the first case, well users pump simultaneously, and in the second one they cooperate so that they pump alternately. This paper proves that the proposed alternate pumping schedule works as a stabilizer, reducing the high hydraulic drawdowns values, regardless of the aquifer characteristics. Moreover, pumping alternately is better in terms of pumping cost, compared to simultaneous pumping, though benefit become negligible as distance between wells becomes large. Two simplified equations are proposed, one to find the difference of the hydraulic drawdowns between the two pumping schedules and the other one to find the economic benefit of each well from cooperation. The equations are finally applied to a number of cases and their results are compared to the results obtained from an algorithm created to calculate the hydraulic drawdowns and the pumping cost, using the Theis equation. The results can be very useful in irrigation scheduling, as they can be applied to systems of well users/farmers, to reduce pumping cost.

Simulation of Transient Flow in Gas Pipelines Using the Finite Volume Method

The transient flow analysis is fundamental to the simulation of natural gas process, in order to adjust the system to real operative conditions and to obtain the highest level of efficiency, compliance and reliability. The simulation of natural gas pipelines and networks requires mathematical models that describe flow properties. Some models that have been developed year after year based on the laws of fluid mechanics that govern this process, interpreted as a system of equations difficult to solve. This investigation describes the fully implicit finite volume method for natural gas pipeline flow calculation under isothermal conditions and transient regime. The simplification, discretization scheme and implementation equations are approached throughout this paper. The model was subjected to two evaluations: sinusoidal variation of the mass flow and opening-closing valve at the outlet of the pipeline, it is compared with two models: fully implicit finite difference method and method of characteristics. This method proved to be efficient in the simulations of slow and fast transients, coinciding the flow oscillations with the natural frequency of natural gas pipeline.

Analysis of Transient Flow Around the Obstacle with Rotated Square Cross Sections using Deep Learning

Analysis of Transient Flow Around the Obstacle with Rotated Square Cross Sections using Deep Learning

A cross-industry assessment of the flow rate-elapsed time profiles of test equipment typically used for dry-powder inhaler (DPI) testing: Part 2– analysis of transient air flow in the testing of DPIs with compendial cascade impactors

We describe a computational model that captures the physics of the unsteady air-flow startup that accompanies the testing of dry-powder inhalers (DPI) with cascade impactors (CIs) specifically when...

Transient flow analysis for multi-state automotive scroll compressors

Due to the merit of high efficiency, low noise and vibration, scroll compressor has been rapidly developed in recent years. The working process of a scroll compressor is a three-dimensional non-constant compressible viscous flow process. In order to optimize the compressor design for better performance, it is necessary to understand and reveal the detailed mechanism of the unsteady flow inside a scroll compressor. In this paper, a three-dimensional flow-field model of scroll compressor is established. Non-stationary transient simulation of the flow field is carried out by using a combination of dynamic grid and User-Defined-Files. The distribution of temperature, pressure and velocity within the flow field of the work gas under different operating conditions were obtained. In this paper, the flow phenomenon of gas reflux at the suction and discharge ports and its effect on the performance of the scroll compressor was analysed.

Analysis of Transient Inhomogeneous Flow and Thermal Characteristics in a Drying Room via Large Eddy Simulation

AbstractTo optimize the flow structure in a soft‐capsule drying room, the notable inhomogeneous characteristics of flow behavior and thermal feature are numerically explored. An advanced three‐dimensional numerical model is established and a verified large eddy simulation (LES) model is adopted. The results indicated that there is a highly inhomogeneous flow structure especially approaching the bilateral region of the drying room, mainly caused by the large velocity gradient whereas a relatively uniform flow structure is observed in the middle region. In the drying process, the inhomogeneous flow feature is sensitive to the increased inlet velocity and aspect ratio λ. It was found that a suitable inlet velocity and a small aspect ratio λ can provide a better drying flow environment.