Propellersimulering genom Computational Fluid Dynamics (CFD) används mer och mer i ett tidigt designstadium gällande fartygs framdrift. Rolls-Royce Hydrodynamic Research Centre har lång erfarenhet av propellerdesign och analysarbete genom både modelltester och numerisk simulering, och CFD används idag för ett flertal olika tillämpningar och syften.   Att utnyttja en tidseffektiv och enkel simuleringsmetod är en betydelsefull strategi och tid gentemot noggrannhet är en avvägning som designers alltid måste göra. I detta fall kommer en förenklad modelleringsprincip studeras där propellern representeras av en cylindrisk volym med samma diameter och proportioner som den faktiska propellern. Denna volym, kallad en aktuatordisk-volym implementeras med framdrivningskrafterna genom inmatning av lokala källtermer i modellen och överför på så vis rörelsemängd till fluiden. Arbetet har fokuserats på utveckling av denna simuleringsmodell och att utvärdera dess prestanda genom jämförelse mot en geometriskt mer komplex propellermodell.   Syftet med detta arbete är att undersöka resultat från en förenklad propellermodell med avseende på inducerat hastighetsfält för en propeller som verkar i ett homogent inflödesfält. Analys av den inducerade hastighetsprofilen är ett viktigt steg i designprocessen för propeller-roder-konfiguration och en beräkningseffektiv metod för att uppnå detta är mycket önskvärd.   Resultat från simuleringarna visar att modelleringsprincipen möjliggör enkel användning av olika propellertyper och förbättrar beräkningseffektiviteten med en tredjedel av tidsåtgången som krävs för den komplexa propellermodellen. Inducerade hastighetsprofiler visar även på relativt god överensstämmelse och modellen erbjuder användbara verktyg för att variera dess utseende. Fortsatt arbete bör övervägas för att optimera diskretiseringsmetod och på så vis även möjliggöra förbättring av lösningstiden, tillsammans med undersökning av icke-uniformt inflödesvillkor inspirerat av strömningen som skapas bakom en fartygskropp. / Propeller simulation by Computational Fluid Dynamics (CFD) is more and more used in an early design stage of marine propulsion. Rolls-Royce Hydrodynamic Research Centre has long experience with propeller design and analysis through both model testing and numerical simulations, and CFD is today used in a wide range of applications and purposes. Utilizing a time efficient and simple simulation approach is a valuable strategy, and time against accuracy is a trade off a designer need to do all the time. In this case the study will concern a modelling approach where the propeller is represented by a cylindrical volume with the same diameter and proportions as an actual propeller. This volume, called an actuator disc volume zone is implemented with the propulsive forces as local source terms into the model and thereby provides momentum into the fluid. Work will be concentrated on developing this simulation model and evaluate its performance by comparison with a more complex propeller geometry model. The purpose of this work is to investigate the result from a simplified propeller model in regard to the induced velocity field for a propeller operating in a homogeneous inflow field. Analysis of the induced velocity profile is an important step in the design process of propeller-rudder configuration and a computationally efficient method in doing this is highly desirable. Results from the simulations show that the modelling approach enables simple employment of different propeller types and improves computational efficiency with a third of required time amount compared to the complex propeller model. The induced velocity profiles also demonstrate a relatively accurate behaviour and the model provide useful tools in altering their appearance. Further work need to be considered in optimizing the discretization method and thereby possibly improve solution efficiency, together with examining of a non-uniform inflow velocity condition inspired by the wake created behind a ship hull.

Mixing in stirred tanks influences conversion of reactants for fast reactions, and the efficiency of a mixing process can be determined from the power consumption and mixing time, which are the two parameters that define homogenization energy. In this study, the computational fluid dynamics (CFD) and laser Doppler velocimetry (LDV) techniques were employed to study the effect of the Rushton turbine bottom clearance on the flow field, mixing time and power consumption in a stirred tank. Experimental and simulation studies were conducted in a tank with and without a draft tube where a conductivity meter and decolourization methods were employed in validating the mixing time simulation results. A good agreement between the experimental and simulation results for the flow field and mixing time was obtained. The results showed a reduction in mixing time and power consumption at a low impeller clearance, with reference to the standard clearance, and a further reduction of the same parameters was obtained for a system fitted with a draft tube. At the low clearance, there was an increase in mixing efficiency by 46%, for a system without draft tube and 61% for that with the draft tube.

This work focuses on an investigation of multi-modality in typical aerodynamic shape optimization problems and development of optimization algorithms that can find a global optimum. First, a classification of problems based on the degree of multi-modality is introduced. Then, two optimization algorithms are described that can find a global optimum in a computationally efficient manner: a gradient-based multi-start Sobol algorithm, and a hybrid optimization algorithm. Two additional algorithms are considered as well: a gradient-based optimizer and a genetic algorithm. Finally, we consider a set of typical aerodynamic shape optimization problems. In each problem, the primary objectives are to classify the problem according to the degree of multi-modality, and to select the preferred optimization algorithm for the problem. We find that typical two-dimensional airfoil shape optimization problems are unimodal. Three-dimensional shape optimization problems may contain local optima. In these problems, the gradient-based multi-start Sobol algorithm is the most efficient algorithm.

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No description available.

A computational study has been performed to investigate the effects of blade row interaction on the performance of radial turbomachines, which was motivated by the need to improve our understanding of the blade row interaction phenomena for further improvement in the performance. High-speed centrifugal compressor stages with three settings of radial gap are configured and simulated using a three-dimensional Navier-Stokes flow method in order to investigate the impact of blade row interaction on stage efficiency. The performance predictions show that the efficiency deteriorates if the gap between blade rows is reduced to intensify blade row interaction, which is in contradiction to the general trend for stage axial compressors, hi the compressors tested, the wake chopping by diffuser vanes, which usually benefits efficiency in axial compressor stages, causes unfavourable wake compression through the diffuser passages to deteriorate the efficiency. Similarly, hydraulic turbine stages with three settings of radial gap are simulated numerically. A new three-dimensional Navier-Stokes flow method based upon the dual-time stepping technique combined with the pseudo-compressibility method has been developed for hydraulic flow simulations. This method is validated extensively with several test cases where analytical and experimental data are available, including a centrifugal pump case with blade row interaction. Some numerical tests are conducted to examine the dependency of the flow solutions on several numerical parameters, which serve to justify the sensitivity of the solutions. Then, the method is applied to performance predictions of the hydraulic turbine stages. The numerical performance predictions for the turbines show that, by reducing the radial gap, the loss generation in the nozzle increases, which has a decisive influence on stage efficiency. The blade surface boundary layer loss and wake flow mixing loss, enhanced with a higher level of flow velocity around blading and the potential flow disturbances, are responsible for the observed trend.

Industrial centrifugal air compressors can require a combination of a large range of mass flow, high efficiency, constant pressure ratio, and constant rotational speed, specifically when used for sewage effluent aeration treatment. In order to achieve this performance it is common to use variable inlet guide vanes (VIGV's). The performance characteristics of an existing VIGV design have been determined using both an experimental test facility and state of art numerical techniques. The results obtained from these techniques are far more comprehensive than earlier fullscale performance testing. Validation of the performance of the existing design using these techniques has led to the development of a new vane design and potential improvements to the inlet ducting geometry. The aerodynamic interaction between the VIGV system and the centrifugal compressor impeller has also been investigated using a 3-D computational model of the complete variable geometry compressor stage. The results of these investigations have been validated by data available from full scale experimental testing. Strong correlation was obtained between numerical and experimental techniques, and a predicted improvement in polytropic efficiency up to 3% at low flow rates using the re-designed variable inlet guide vanes has been achieved. The overall outcome of this research is a usable VIGV design technique for real industrial compressor environments, and confirmation that an acceptable design can be achieved that represents a rewarding improvement in performance.

This work focuses on an investigation of multi-modality in typical aerodynamic shape optimization problems and development of optimization algorithms that can find a global optimum. First, a classification of problems based on the degree of multi-modality is introduced. Then, two optimization algorithms are described that can find a global optimum in a computationally efficient manner: a gradient-based multi-start Sobol algorithm, and a hybrid optimization algorithm. Two additional algorithms are considered as well: a gradient-based optimizer and a genetic algorithm. Finally, we consider a set of typical aerodynamic shape optimization problems. In each problem, the primary objectives are to classify the problem according to the degree of multi-modality, and to select the preferred optimization algorithm for the problem. We find that typical two-dimensional airfoil shape optimization problems are unimodal. Three-dimensional shape optimization problems may contain local optima. In these problems, the gradient-based multi-start Sobol algorithm is the most efficient algorithm.

A parallel, block-based, three-dimensional, hexahedral finite-volume scheme with adaptive mesh refinement has been developed for the solution of the 10-moment Gaussian closure for the modelling of fully three-dimensional micro-scale, non-equilibrium flows. The Gaussian closure has been shown to be a more effective tool for modelling rarefied flows lying within the transition regime than the Navier-Stokes equations, which encounter mathematical difficulties approaching free-molecular flows, and is computationally less expensive than particle-based methods for flows approaching the continuum limit. The hyperbolic nature of the moment equations is computationally attractive and the generalized transport equations can be solved in an accurate and efficient manner using Godunov-type finite-volume schemes as considered here. Details are given of the Gaussian closure, along with extensions for diatomic gases and slip-flow boundaries. Numerical results for several canonical flows demonstrate the potential of these moment closures and the parallel solution scheme for accurately predicting fully three-dimensional non-equilibrium flow behaviour.

The effects of pressure on various properties of ten different syngas fueled flames were analyzed using one and two dimensional simulations. One-dimensional premixed flames were modeled in CANTERA. Flame speed, adiabatic flame temperature and thermal diffusivity as functions of equivalence ratio and pressure were quantified for the fuels using four chemical kinetic mechanisms. Data from the different mechanisms displayed good agreement with data from previous experimental benchmarks. Two-dimensional axisymmetric co-flow flames were simulated in a state of the art computational framework for modeling laminar flames. Flame structure comparisons were made with past experimental and numerical results as well as with theoretical predictions. Good agreement in stoichiometric flame height was observed with past theoretical and numerical flame height measurements. Visible flame heights had little correlation with the stoichiometric flame heights. The flame radius was also noted to be proportional to p^-0.35 at high pressures instead of p^-0.5 as predicted by theory.