NUMERICAL INVESTIGATION OF THE TURBULENT FLOW PARAMETERS DISTRIBUTION IN A PARTLY PERFORATED HORIZONTAL WELLBORE

The overall pressure drop in a horizontal wellbore used in the recovery of oil and gas industry was classified into four separate effects due to wall friction, increase in momentum, perforation roughness and type of fluid mixing. A perforated section is followed by a plain section for many horizontal wells. The additional pressure drop due to combined effect of perforation roughness and the type of fluid mixing was analyzed through numerical CFD and the results were compared with the experimental results of other researchers. The computations were based on the finite volume method with the SIMPLE algorithm standard ε−kmodel. The pipe was used geometrically similar to the real perforated wellbore with 60 ̊ phasing, 6 SPF (shoot per foot) and the pitch of the perforations 60 mm (the number of perforations in this paper are less than experimental pipe). The parameters that are being investigated are pressure drops of the pipe and so far simulations have been carried out for an inlet pipe Reynolds numbers ranging from 28,773 to 90,153 for the total flow rate ratio ranging from 0% to 100%. Numerical simulations were performed using CFX of ANSYS FLUENT 13, where the governing equations of mass and momentum were solved simultaneously, using the two equations of standard k-ε turbulence model. As the rate of flow through the perforations increases i.e. with the increase in flow rate ratio, the total pressure increases due to large acceleration pressure drop for higher flow rate through the perforations. The increases in perforations number increase the total pressure drop and vice versa. The numerical results agreed with the experimental work

Numerical Simulation of Jet Injection and Species Mixing under High-Pressure Conditions

Direct Numerical Simulation (DNS) and Large Eddy Simulation (LES) are performed of a round fluid jet entering a high-pressure chamber. The chemical compositions and temperatures of the jet and that of the fluid in the chamber are initially prescribed. The governing equations consist of the conservation equations for mass, momentum, species and energy, and are complemented by a real-gas equation of state. The fluxes of species and heat are written in the framework of fluctuation-dissipation theory and include Soret and Dufour effects. For more than two species, the full mass diffusion and thermal diffusion matrices are computed using high-pressure mixing rules which utilize as building blocks the corresponding binary diffusion coefficients. The mixture viscosity and thermal conductivity are computed using standard mixing rules and corresponding states theory. To evaluate the physical model and numerical method, LES is employed first to simulate a supercritical N_2 jet injected into N_2. Time averaged results show reasonable agreement with the experimental data. Then, DNS is conducted to study the spatial evolution of a supercritical N_2 jet injected into CO_2. Time averaged results are used to compute the length of the potential core and the species diffusion characteristics. Spectral analysis is then applied on a time series data obtained at several axial locations and a dominant frequency is observed inside the potential core

Numerical Research About the Internal Flow of Steam-jet Vacuum Pump: Evaluation of Turbulence Models and Determination of the Shock-mixing Layer

AbstractSteam-jet vacuum pump is widely used in a range of applications. This paper evaluated the performance of four well-known turbulence models for predicting and understanding the internal flow of a steam-jet vacuum pump first. With the help of a commercial computational fluid dynamics (CFD) code ANSYS-Fluent 6.3, the simulation results obtained from the concerned turbulence models were compared with experimental values, the k-omega-SST model was chosen as a tool model for carrying out numerical simulations. Then, based on the simulation results obtained from specific operating conditions, a method for locating the shock-mixing layer was put forward. The shape of the shock-mixing layer shows that the secondary steam does not mix with the primary steam immediately after being induced into the mixing chamber of the pump; actually, they maintain their independence till the shocking position instead. After the shock happens, the shock-mixing layer disappear, the two fluid in the pump begin to mix with each other and discharge to the next stage with almost the same state. Based on the shape of the shock-mixing layer and the supersonic region of the secondary steam, a detailed analysis for the flow duct of the secondary steam was carried out. It is found that the throat of the secondary steam flow duct plays a crucial role in maintaining a stable operating state and the length of the throat reflects the back pressure endurance for the pump

Liquid droplets and gas interactions in two-phase flow

The work focuses on the interactions of the two phases (liquid and gas) in droplet flows. Most studies of sprays do not resolve the liquid phase nor the near field and droplets are treated as point sources of mass, momentum, energy and species. In the present work, two- and three-dimensional Direct Numerical Simulations of fully resolved droplet arrays are analysed. Simulations of droplets arrays in inert and reacting environments are performed and evaporation rates and fuel vapour mixing in laminar and turbulent flows are assessed. The novel model developed in this work combines the one- and two-fluid formulations for multiphase flows. The energy transport equation is solved based on a one-fluid formulation while the species, velocities and pressure equations are solved with a two-fluid formulation. In addition, a Level Set technique is combined with the Ghost Fluid method in a mass conserving approach in order to track the liquid interfaces. The numerical algorithm was parallelised in order to satisfy the computational demand of the simulations. The validation tests performed show that the model implemented is able to capture the dynamic behavior of droplet interactions and heat and mass transfer across interfaces. The effects of turbulence and droplet density on droplet evaporation rates in reacting flows is investigated for n-heptane and kerosene droplet arrays. The evaporation rates are compared to existing models commonly used in Large Eddy Simulations and Reynolds-averaged Navier-Stokes computations. A shell around the droplet approach is proposed in order to estimate the gas properties used in these models. It is noted that this approach allows the models to capture transients and provides predictions of the evaporation rates with errors around 2%. The gas phase mixing is assessed by examining the distribution of scalar dissipation. Novel multi-conditional models are proposed that use mixture fraction, distance to previous droplet and zone of location as the conditioning variables for the scalar dissipation. The scalar dissipation is found to be well predicted in terms of magnitude and distribution. The accurate representation of the mean scalar dissipation is achieved. The b-PDF description of the mixture fraction seems to capture well the global behaviour for a laminar environment and for time averaged results in the turbulent cases.Open acces

Second Order Fully Discrete Energy Stable Methods on Staggered Grids for Hydrodynamic Phase Field Models of Binary Viscous Fluids

We present second order, fully discrete, energy stable methods on spatially staggered grids for a hydrodynamic phase field model of binary viscous fluid mixtures in a confined geometry subject to both physical and periodic boundary conditions. We apply the energy quadratization strategy to develop a linear-implicit scheme. We then extend it to a decoupled, linear scheme by introducing an intermediate velocity term so that the phase variable, velocity field, and pressure can be solved sequentially. The two new, fully discrete linear schemes are then shown to be unconditionally energy stable, and the linear systems resulting from the schemes are proved uniquely solvable. Rates of convergence of the two linear schemes in both space and time are verified numerically. The decoupled scheme tends to introduce excessive dissipation compared to the coupled one. The coupled scheme is then used to simulate fluid drops of one fluid in the matrix of another fluid as well as mixing dynamics of binary polymeric, viscous solutions. The numerical results in mixing dynamics reveals the dramatic difference between the morphology in the simulations obtained using the two different boundary conditions (physical vs. periodic), demonstrating the importance of using proper boundary conditions in fluid dynamics simulations

Numerical Modeling of Self-Pressurization and Pressure Control by Thermodynamic Vent System in a Cryogenic Tank

This paper presents a numerical model of a system-level test bed - the multipurpose hydrogen test bed (MHTB) using Generalized Fluid System Simulation Program (GFSSP). MHTB is representative in size and shape of a fully integrated space transportation vehicle liquid hydrogen (LH2) propellant tank and was tested at Marshall Space Flight Center (MSFC) to generate data for cryogenic storage. GFSSP is a finite volume based network flow analysis software developed at MSFC and used for thermo-fluid analysis of propulsion systems. GFSSP has been used to model the self-pressurization and ullage pressure control by Thermodynamic Vent System (TVS). A TVS typically includes a Joule-Thompson (J-T) expansion device, a two-phase heat exchanger, and a mixing pump and spray to extract thermal energy from the tank without significant loss of liquid propellant. Two GFSSP models (Self-Pressurization & TVS) were separately developed and tested and then integrated to simulate the entire system. Self-Pressurization model consists of multiple ullage nodes, propellant node and solid nodes; it computes the heat transfer through Multi-Layer Insulation blankets and calculates heat and mass transfer between ullage and liquid propellant and ullage and tank wall. TVS model calculates the flow through J-T valve, heat exchanger and spray and vent systems. Two models are integrated by exchanging data through User Subroutines of both models. The integrated models results have been compared with MHTB test data of 50% fill level. Satisfactory comparison was observed between test and numerical predictions

Simulation of supercritical Diesel jets using the PC-SAFT EoS

A numerical framework has been developed to simulate supercritical Diesel injection using a compressible density-based solver of the Navier-Stokes equations along with the conservative formulation of the energy equation. Multi-component fuel-air mixing is simulated by considering a diffused interface approximation. The thermodynamic properties are predicted using the Perturbed Chain Statistical Associating Fluid Theory (PC-SAFT) real-fluid equation of state (EoS). This molecular-based EoS requires three empirically determined but well-known parameters to model the properties of a specific component, and thus, there is no need for extensive model calibration, as is typically the case when the NIST library is utilised. Moreover, PC-SAFT can handle flexibly the thermodynamic properties of multi-component mixtures, which is an advantage compared to the NIST library, where only limited component combinations are supported. This has allowed for the properties of Diesel fuel to be modelled as surrogates comprising four, five, eight and nine components. The proposed numerical approach improves the overall computational time and overcomes the previously observed spurious pressure oscillations associated with the utilization of conservative schemes. In the absence of experimental data, advection test cases and shock tube problems are included to validate the developed framework. Finally, two-dimensional simulations of planar jets of n-dodecane and a four component Diesel surrogate are included to demonstrate the capability of the developed methodology to predict supercritical Diesel fuel mixing into air

A numerical solution of the Navier-Stokes equations for supercritical fluid thermodynamic analysis

An explicit numerical solution of the compressible Navier-Stokes equations is applied to the thermodynamic analysis of supercritical oxygen in the Apollo cryogenic storage system. The wave character is retained in the conservation equations which are written in the basic fluid variables for a two-dimensional Cartesian coordinate system. Control-volume cells are employed to simplify imposition of boundary conditions and to ensure strict observance of local and global conservation principles. Non-linear real-gas thermodynamic properties responsible for the pressure collapse phenomonon in supercritical fluids are represented by tabular and empirical functions relating pressure and temperature to density and internal energy. Wall boundary conditions are adjusted at one cell face to emit a prescribed mass flowrate. Scaling principles are invoked to achieve acceptable computer execution times for very low Mach number convection problems. Detailed simulations of thermal stratification and fluid mixing occurring under low acceleration in the Apollo 12 supercritical oxygen tank are presented which model the pressure decay associated with de-stratification induced by an ordinary vehicle maneuver and heater cycle operation

CFD SIMULATION AND SHAPE OPTIMIZATION OF SUPERSONIC EJECTORS FOR REFRIGERATION AND DESALINATION APPLICATIONS

The aim of this thesis is to investigate the detailed flow field inside the supersonic ejector using numerical methods and to optimize the ejector’s mixing chamber wall shape to obtain a maximum entrainment ratio (ER) in order to obtain the highest possible efficiency that can be attained by the ejector. A steam ejector applied in the cooling industry is first studied to determine the most accurate turbulence model for its supersonic jet flow field simulation with mixing with the entrained steam in the mixing chamber. A commercial Computational Fluid Dynamics (CFD) package FLUENT 14.5 along with the meshing tool ICEM 14.5 is utilized to conduct the modeling and simulation to examine the ejector performance using two different turbulence models: k-ε realizable and k-ω SST. Velocity contours, pressure plots and entrainment ratio plots obtained from FLUENT are studied to investigate the effects of several ejector operating conditions as well as to verify the turbulence model accuracy by comparing the numerical results with experimental data. Simulations for three different supersonic ejectors (ejectors for refrigeration and desalination application with different working fluids namely the steam or compressed air) are conducted to further validate the numerical solution accuracy. The turbulence model producing more accurate results is applied to all three cases. In second part of the thesis, a single objective genetic algorithm (SOGA) is employed to optimize the mixing chamber wall shape for steam ejector for refrigeration to achieve the maximum entrainment ratio. Bezier Curves are used to generate the new wall shapes. The whole shape generation-meshing-simulation-SOGA process is repeated until the ER converges to a maximum value based on the specified convergence criteria for SOGA