RNG in turbulence and modeling of bypass transition

Two projects are considered: the Renormalization Group (RNG) analysis of turbulence modeling, and the calculation of bypass transition through turbulence modeling. RNG is a process which eliminates small scales on the uneliminated large scales as the change in the transport properties. It is because of this property of RNG that it was previously suggested that RNG could be used as a model builder in turbulence modeling. The possibility is studied of constructing RNG based turbulence models, and to try to proceed to do the modeling through RNG in parallel with the classical approach. The numerical predictions made by RNG models and by classical models is compared against data from Direct Numerical Simulation. While in an environment with freestream turbulence, the transition initiated by the instability of the laminar boundary layer to Tollmien-Schlichting waves is found to be a bypass one in which turbulent spots are formed without T-S wave amplification. The formation is a random process, and flow within a turbulent spot is almost fully turbulent. This suggests the possibility of using turbulence modeling to describe and predict the bypass transition

Center for Modeling of Turbulence and Transition (CMOTT). Research briefs: 1990

Brief progress reports of the Center for Modeling of Turbulence and Transition (CMOTT) research staff from May 1990 to May 1991 are given. The objectives of the CMOTT are to develop, validate, and implement the models for turbulence and boundary layer transition in the practical engineering flows. The flows of interest are three dimensional, incompressible, and compressible flows with chemistry. The schemes being studied include the two-equation and algebraic Reynolds stress models, the full Reynolds stress (or second moment closure) models, the probability density function models, the Renormalization Group Theory (RNG) and Interaction Approximation (DIA), the Large Eddy Simulation (LES) and Direct Numerical Simulation (DNS)

Effects Of Drill-pipe Whirling Motion On Cuttings Transport Performance For Horizontal Drilling

Dispersion, deposition, and suspension of particulate materials in the carrier fluid play a significant role in the oil industry. Increasing the cuttings transport performance in deviated wells is difficult due to the rolling/sliding transport, and cuttings settling on the low side of the annulus. Insufficient cuttings transport may lead to some crucial problems such as pipe sticking, increasing in torque and drag, material damage and bed cementing quality. Increasing flow rates and improving mud properties may not be applicable for a proper hole cleaning because of the hydraulic and mechanical limitations. In such cases, additional pressure may be generated, and this causes formation fractures and drilling fluid losses. Under these circumstances, the other major contribution to cuttings transport is provided by drill-pipe rotation. In this study, the effect of drill-pipe rotation on cuttings transport behavior is investigated for eccentric horizontal wells. Whirling motion of drill-pipe is also analyzed. During drilling, drill-pipe is subjected to axial, lateral and torsional loads due to the dynamic vibrations. These loads cause that drill-pipe to lose its stability and generate snaking and/or whirling type of motion. Dynamic behavior of drill-pipe plays a significant role on cuttings transport and stationary bed removal. Turbulence modeling becomes very complicated when cuttings transport includes deposition and sliding effects. Advanced turbulence models are required to get accurate flow predictions while optimizing computational resources requirements. Unsteady SST k-ω turbulence model is applied due to its practicability and reliability in predicting cuttings transport behavior. Discrete phase is modeled with discrete element method (DEM) by including particle-particle and particle-fluid interactions with a commercial ANSYS FLUENTTM 15.0 CFD package using LSU high performance computing (HPC) resources. It is concluded that cuttings concentration significantly decreases with increasing flow rate. Drill-pipe rotation around its own axis causes cuttings swaying and distribute asymmetrically along the circumferential direction. Orbital motion of the drill-pipe contributes more to cuttings transport performance. Low whirling rotary leads to increase in annular pressure losses in low flow rates. In the turbulent flow regime, however, annular pressure losses increase with increasing whirling speed

Numerical and Experimental Investigation of the Morphology Development of Expansion Clouds by a Powder Jet Flow

Explosion suppression is often the preferred method of explosion attenuation in industry. The morphology development of suppression clouds is important for the design of necessary coverage of the product. This paper presents a numerical and experimental investigation of the growth of powder dispersion as it expands from a discharge nozzle. A Lagrangian stochastic particle-tracking approach and the RNG k-e turbulence model are adopted in the flow field solver for the dispersed and continuous phases. The flow fields coupled with the particle interactions are predicted. The dispersion characteristics of the expansion of the powder cloud through a pipe for short intervals of time are investigated. This was compared with (1) captured images from experiments, (2) experimental data, and (3) results of previous simulations. Particle positions along the jet are presented. The effects of flow rate on the development of the cloud and a comparison with experimental results are also presented. It is noted that the coverage of the powder cloud can be controlled by the flow rate of the jet, and the developing length of the cloud is more influenced by the flow rate of jet flow than the developing width. The good qualitative agreements achieved are useful for further optimisation of product design

Numerical Prediction of Turbulent Oscillating Flow and Heat Transfer in Pipes with Various End Geometries

Unsteady flow is present in man, machine and nature. The flow of blood in arteries and capillaries in the human body is pulsatile-composed of a mean flow superposed with an oscillating component. The tides that wash in and out of rivers, harbors and estuaries are unsteady flows with very long periods of oscillation. Many engineering devices employ pulsatile and oscillating flow. Pulsating flow is defined here as a periodic flow with a net displacement of fluid over each flow cycle. Oscillating flow is defined as a period flow with a zero mean over each cycle. The subject of this thesis is oscillating flow and heat transfer in pipes which make up the heater and cooler sections of the NASA Space Power Research Engine (SPRE) currently under development. This engine uses the Stirling cycle as the thermal energy converter in a power plant for future space applications. The information presented in this thesis will of course be applicable to the design of many types of machinery which employ oscillating flow and heat transfer

CFD simulation of horizontal oil-water flow with matched density and medium viscosity ratio in different flow regimes

Simulation of horizontal oil-water flow with matched density and medium viscosity ratio (μo/μw=18.8) in several different flow regimes (core annular flow, oil plugs/bubbles in water and dispersed flow) was performed with the CFD package FLUENT in this study. The volume of fluid (VOF) multiphase flow modeling method in conjunction with the SST k-ω scheme was applied to simulate the oil-water flow. The influences of the turbulence schemes and wall contact angles on the simulation results were investigated for a core annular flow (CAF) case. The SST k-ω turbulence scheme with turbulence damping at the interface gives better predictions than the standard k-ε and RNG k-ε models for the case under consideration. The flow regime of density-matched oil-water flow with medium viscosity ratio, or more generally speaking, the flow regime of fluids where the surface tension is playing a prevailing role is sensitive to the wall contact angle. Simulation results were compared with experimental counterparts. Satisfactory agreement in the prediction of flow patterns were obtained for CAF and oil plugs/bubbles in water. The simulation results also demonstrated some detailed flow characteristics of CAF with relatively low-viscosity oil (oil viscosity one order higher than the water viscosity in the present study compared to the extensively studied CAF with oil viscosity being two to three orders higher than the water viscosity). Different from the velocity profiles of high-viscosity oil CAF where there is sharp change in the velocity gradient at the phase interface with velocity across the oil core being roughly flat, there is no sharp change in the velocity gradient at the phase interface for CAF with relatively low-viscosity oil

Numerical simulation of flows in concentric and eccentric annulus – relevant to geothermal wells

Master's thesis in Petroleum engineeringAt the end of 20th century, the utilization of geothermal energy has increased by 150% forming a solid industry of relevant importance on global markets (Dickson & Fanelli, 2004). According to numerous analyses, this type of energy exploitation has a strong forecast of development in the future. High potential of progress is associated with complex studies to ensure the feasibility, safety and profitability of the investments. Numerical simulation of flows in geothermal exploitation is an essential tool to establish adequate results. The assessment of this process is a key factor for preparing schemes providing high overall efficiency (Vasini et al., 2017). Determining the most favorable parameters and approaches is the subject of plenty studies in the field of geothermal energy. This work analyzes the concept of geothermal energy and heat transfer in general, and in the wellbore. Furthermore, it investigates application of separate turbulence models on flow in concentric and eccentric annulus. Different assembly of pipes require adjusting diverse approaches to achieve finest results. When chosen models work for theoretical configurations, they do not automatically comply for the field cases. As for the eccentricity, the simulation shows valuable data of how the flow behaves in irregular, but very common position. Obtained results satisfy the benchmarks stated in the preceding researches. For instance, the thermal structures are more aroused near the outer wall of the assembly, than closer to the inner pipe. This outcome might be implemented in analyzing vortex generations in the annuli. Moreover, the study defines the dependence of heat transfer rate on the pipe materials. Conducted research might be used as an initial and easy to comprehend overview of the heat transfer phenomena in geothermal energy exploitation

Towards improved understanding and optimization of the internal hydraulics of chlorine contact tanks

2012 Spring.Includes bibliographical references.The research presented in this thesis focuses on utilizing computational fluid dynamics (CFD) to further the understanding of the internal flow dynamics in chlorine contact tanks. In particular, we aim to address the following two critical questions: (1) for a given footprint of a serpentine chlorine contact tank with a fixed inlet configuration, how does the hydraulic efficiency of the tank depend on the configuration of internal baffles?, and (2) for water storage tanks modified for use as chlorine contact tanks, can inlet conditions be modified such that near plug flow conditions are induced close to the inlet and throughout the rest of the tank? Key design parameters were identified and parametrically tested for each of these design problems. For the serpentine baffle tanks, a benchmark contact tank geometry based on a scaled model of the Embsay chlorine contact tank in Yorkshire, England was used for validation and then subsequently modified by varying both the number and length of baffles. In order to define guidelines for hydraulically efficient baffle tanks, a parametric study consisting of forty high-resolution 3-D simulations of different tank configurations were performed to quantify the efficiency of the scaled contact tank as a function of the dimensional relationships between the inlet width, channel width, tank width, tank length, and baffle opening lengths. The simulations tested the hydraulic efficiencies of the different tank configurations. Hydraulic efficiency was quantified by the baffle factor (BF). We found that the most efficient tank had a BF of 0.71, and that hydraulic efficiency was optimized in this tank by maximizing the length to width ratio in baffle chambers and by minimizing flow separation through the tank, which was achieved by setting equal dimensions to the inlet width, channel width, and baffle opening length. A new contact tank geometry was then developed by applying the dimensional relationships that were shown by the parametric study to optimize BF, and by modifying the baffle geometries to minimize flow separation around baffle tips. The new contact tank design had a BF of 0.78, which represents a 10 percent improvement in hydraulic efficiency compared to the Embsay contact tank. In the study of inlet modifications for cylindrical storage tanks, inlet diffusers and inlet manifolds were developed and modeled. Experimental flow through curves (FTCs) of a benchmark storage tank used as a contact tank were used to validate the CFD model that was utilized in the study. Thirty-seven modified inlet configurations using two representative flow rates were modeled. The inlet manifolds improved BF significantly, whereas the inlet diffuser had insignificant effects. The key design parameters identified for the inlet manifold were the number of inlets and the height of the inlet(s) in the tank. The inlet manifold designed with 16 inlets with the inlet height set at 10 percent of the tank height improved the BF of the storage tank from 0.16 to 0.51. This 220 percent increase in BF represents a major improvement in hydraulic efficiency for such cylindrical contact tanks that are widely used by small water treatment systems

CFD Study of Taylor-Like Vortices in Swirling Flows

Swirling flows are complex fluid motions that appear in various natural phenomena and man-made devices. Numerous engineering applications such as turbomachinery, jet engine combustion chambers, mixing tanks and industrial burners involve swirling flows. This wide range of applications is due to unique characteristics offered by swirling flows such as increase in mixing rate, heat transfer rate and wall shear stress. In this study the axisymmetric swirling flow behavior in the context of a hybrid rocket engine have been analyzed. While modeling the flow inside a cylindrical chamber using CFD, a similarity with the Taylor vortices instability has been observed. Similar to the classic Taylor-Couette flow system, a secondary flow field in the form of wavy toroidal vortices spaced regularly along the axial direction appear under certain critical conditions. The dimensionless control parameter governing the formation of the Taylor-like vortices is expressed as the ratio of the tangential to axial velocity components