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1
Welsh, Stephanie. "Compressible Taylor-Couette flow." Thesis, University of Leeds, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.616475.
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Incompressible Taylor-Couette flow has been studied extensively over the years. However, the compressible system has been largely ignored with only a few notable studies. The present thesis aims to explore the compressible Taylor-Couette system for a large range of parameters. The compressible equations have been linearised and a spectral method was applied to solve the system using a MATLAB-routine. In Chapter 2, we discuss the analysis performed to solve the system and explain the basic concepts and phenomena we expect to find. We also explain the numerical methods used. Chapter 3 discusses the case in which the outer cylinder remains motionless. The most important parameters, the Mach and Prandtl number and the radius ratio, are varied. In Chapters 4 and 5, the same procedure is applied to the cases of the co- and counter-rotating cylinders, respectively.
2
Zwart, Philip J. "Grid turbulence in compressible flow." Thesis, University of Ottawa (Canada), 1996. http://hdl.handle.net/10393/10207.
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The flow downstream of a grid in a wind tunnel is of considerable interest for two reasons. Theoretically, it represents a good approximation to the idealized concept of homogeneous and isotropic turbulence, and therefore provides a benchmark to evaluate various analytical theories of turbulence. On the practical side, grids and screens are used extensively in the management of turbulence in a variety of applications. Experimental studies of grid turbulence are numerous in incompressible flow but far scarcer in compressible flow. The present study considers the characteristics of grid turbulence over a range of Mach numbers, M, ranging from the essentially incompressible (M = 0.16), through the moderate subsonic ($0.16 M 0.7)$ and high subsonic $(0.7 M 1.0),$ to the supersonic (M = 1.55). The experiments comprise flow visualization, performed with the shadowgraph method, and mean and fluctuating velocity measurements, made with a laser-Doppler velocimeter. Characteristics of the flow near the grid were visualized in a demonstration nozzle using the schlieren technique. In the moderate subsonic regime, flow visualization indicated that the flow near the grid underwent major changes as M increased. The turbulence intensity and decay characteristics were also found to be influenced, which was attributed to the changes in the flow near the grid. In the high subsonic regime, an unsteady quasi-normal shock was present in the test section. This induced relatively large velocity fluctuations and anisotropic turbulence. In the supersonic regime, stationary oblique shocks generated by the grid were present throughout the test section, which interfered with the turbulence and introduced errors in the measurement technique.
3
Laurantzon, Fredrik. "Flow Measuring Techniques in Steady and Pulsating Compressible Flows." Licentiate thesis, KTH, Mekanik, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-26344.
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This thesis deals with flow measuring techniques applied on steady and pulsatingflows. Specifically, it is focused on gas flows where density changes canbe significant, i.e. compressible flows. In such flows only the mass flow ratehas a significance and not the volume flow rate since the latter depends onthe pressure. The motivation for the present study is found in the use of flowmeters for various purposes in the gas exchange system for internal combustionengines. Applications can be found for instance regarding measurements of airflow to the engine, or measurements of the amount of exhaust gas recirculation.However the scope of thesis is wider than this, since the thesis aims toinvestigate the response of flow meters to pulsating flows. The study is mainlyexperimental, but it also includes an introduction and discussion of several inindustry, common flow measuring techniques.The flow meters were studied using a newly developed flow rig, designedfor measurement of steady and pulsating air flow of mass flow rates and pulsefrequencies typically found in the gas exchange system of cars and smallertrucks. Flow rates are up to about 200 g/s and pulsation frequencies from 0 Hz(i.e. steady flow) up to 80 Hz. The study included the following flow meters:hot-film mass flow meter, venturi flowmeter, Pitot tube, vortex flowmeter andturbine flowmeter. The performance of these meters were evaluated at bothsteady and pulsating conditions. Furthermore, the flow under both steady andpulsating conditions were characterized by means of a resistance-wire basedmass flow meter, with the ability to perform time resolved measurements ofboth the mass flux ρu, and the stagnation temperature T0.Experiments shows that, for certain flow meters, a quasi-steady assumptionis fairly well justified at pulsating flow conditions. This means that thefundamental equations describing the steady flow, for each instant of time,is applicable also in the pulsating flow. In the set-up, back-flow occurred atcertain pulse frequencies, which can result in highly inaccurate output fromcertain flow meters, depending on the measurement principle. For the purposeof finding means to determine when back flow prevails, LDV measurementswere also carried out. These measurements were compared with measurementsusing a vortex flow meter together with a new signal processing technique basedon wavelet analysis. The comparison showed that this technique may have apotential to measure pulsating flow rates accurately.Descriptors: Flow measuring, compressible flow, steady flow, pulsating flow,hot-wire anemometry, cold-wire anemometry.QC 20101208
4
Lanerolle, Lyon Werner John. "Numerical modelling of turbulent compressible flow." Thesis, University of Oxford, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.362004.
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Oo, Htet Htet Nwe. "Actuator Disk Theory for Compressible Flow." DigitalCommons@CalPoly, 2017. https://digitalcommons.calpoly.edu/theses/1727.
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Because compressibility effects arise in real applications of propellers and turbines, the Actuator Disk Theory or Froude’s Momentum Theory was established for compressible, subsonic flow using the three laws of conservation and isentropic thermodynamics. The compressible Actuator Disk Theory was established for the unducted (bare) and ducted cases in which the disk was treated as the only assembly within the flow stream in the bare case and enclosed by a duct having a constant cross-sectional area equal to the disk area in the ducted case. The primary motivation of the current thesis was to predict the ideal performance of a small ram-air turbine (microRAT), operating at high subsonic Mach numbers, that would power an autonomous Boundary Layer Data System during test flights. The compressible-flow governing equations were applied to a propeller and a turbine for both the bare and ducted cases. The solutions to the resulting system of coupled, non-linear, algebraic equations were obtained using an iterative approach. The results showed that the power extraction efficiency and the total drag coefficient of the bare turbine are slightly higher for compressible flow than for incompressible flow. As the free-stream Mach increases, the Betz limit of the compressible bare turbine slightly increases from the incompressible value of 0.593 and occurs at a velocity ratio between the far downstream and the free-stream that is lower than the incompressible value of 0.333. From incompressible to a free-stream Mach number of 0.8, the Betz limit increases by 0.021 while its corresponding velocity ratio decreases by 0.036. The Betz limit and its corresponding velocity ratio for the ducted turbine are not affected by the free-stream Mach and are the same for both incompressible and compressible flow. The total drag coefficient of the ducted turbine is also the same regardless of the free-stream Mach number and the compressibility of the flow; but, the individual contributions of the turbine drag and the lip thrust to the total drag differs between compressible and incompressible flow and between varying free-stream Mach numbers. It was concluded that overall compressibility has little influence on the ideal performance of an actuator disk.
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Bonner, Michael Patrick. "Compressible subsonic flow on a staggered grid." Thesis, University of British Columbia, 2007. http://hdl.handle.net/2429/32290.
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This work focuses on numerically modelling the dynamics of a single phase
fluid at varying densities and pressures. We explore the potential of incompressible
flow simulation methods in modelling compressible flow, with
an eye towards computer animation applications. The methods developed
capture the interesting thermodynamic effects of compressible flow, and reduce
to the standard Marker and Cell incompressible flow Poisson matrix
in the incompressible limit. The method works well in modelling flows in
the subsonic range that normal incompressible techniques do not capture
and where compressible methods are inefficient. We have also investigated
adapting these techniques to granular elastic-plastic flow.Science, Faculty of
Computer Science, Department of
Graduate
7
Farooq, Muhammad Asif. "Cartesian Grid Method for Compressible Flow Simulation." Doctoral thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for energi- og prosessteknikk, 2012. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-16538.
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The Cartesian grid method is an alternative to the existing methods to solve a physical problem governed by partial differential equations (PDEs) computationally. Researchers are interested in this method due to its simplicity of grid generation, less computational effort and ease of implementation into a computer code. One of the other options to solve a physical PDE problem is by the body-fitted grid method. In the body-fitted grid method, the boundary points are grid points. This is not the case with the Cartesian grid method where the body wall is embedded as a boundary into a Cartesian grid resultingin irregular cells near the embedded boundary. These irregular cells near the embedded boundary are known as cut-cells. Instead of using special treatmentsof the cut-cells or enforcing the presence of the embedded boundary by adding source terms at the Cartesian grid points near the boundary, the kinematic and other boundary conditions can be introduced in the Cartesian grid method via ghost points. Those grid points which lie inside the embedded boundary and are also a part of computation are called ghost points. Inactive grid points inside the embedded boundary are referred to as solid points. In the present Cartesian grid method, based on a ghost point treatment, local symmetry conditions are imposed at the embedded wall boundary. The ghost point treatments available in the literature are difficult to implement due to complex procedures. We are introducing a new approach to approximate the kinematics of the embedded boundary by a very simple ghost point treatment called the simplified ghost point treatment. In this approach, we consider the grid lines in the x- and y- directions as approximations of the lines normal to the embedded boundary depending on whether the angle between the normal and the x- or y-directions is closer. For 1D hyperbolic nonlinear systems of conservation laws, we use the moving normal shock wave as a test case for the 1D compressible Euler equations.For the 2D compressible Euler equations, we test the simplified ghost point treatment for an oblique shock wave generated by a wedge. Then, we verified our approach for slender bodies, namely for supersonic flow over a circular arc airfoil and for transonic flow over a circular arc bump in a channel. In a final problem, we applied the simplified ghost point treatment to blunt body flow and considered supersonic flows over a cylinder using the 2D compressible Euler and Navier-Stokes equations. The results are good or comparable to those found in the existing literature.
8
Lin, Hong-Chia. "Topics in Numerical Computation of Compressible Flow." Thesis, Cranfield University, 1990. http://dspace.lib.cranfield.ac.uk/handle/1826/4555.
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This thesis aims to assist the development of a multiblock
implicit Navier-Stokes code for hypersonic flow applications.
There are mainly three topics, which concern the understanding
of basic Riemann solvers, the implementing of implicit zonal
method, and grid adaption for viscous flow.
Three problems of Riemann solvers are investigated. The
post-shock oscillation problem of slowly moving shocks is
examined, especially for Roe's Riemann solver, and possible cures
are suggested for both first and second order schemes. The
carbuncle phenomenon associated with blunt body calculation is
cured by a formula based on pressure gradient, which will not
degrade the solutions for viscous calculations too much. The
grid-dependent characteristic of current upwind schemes is also
demonstrated.
Several issues associated with implicit zonal methods are
discussed. The effects of having different mesh sizes in
different zones when shock present are examined with first order
explicit scheme and such effects are shown to be unwanted
therefore big mesh size change should be avoided. Several
implicit schemes are tested for hypersonic flow. The
conservative DDADI scheme is found to be the most robust one. A
simple and robust implicit zonal method is demonstrated. A
proper treatment of the diagonal Jacobian and choosing the
updating method are found to be crucial.
The final topic concerns the calculation and grid adaption
of viscous flow. We study the linear advection-diffusion equation
thoroughly. The results are unfortunately not applicable to
Navier-Stokes equations directly. Nevertheless a suggestion on
the mesh size control for viscous flow is made and demonstrated.
An attempt to construct a cell-vertex TVD scheme is
described in the appendix.
9
Blank, Henrik. "Numerical methods for compressible and incompressible flow." Thesis, University of Oxford, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.300125.
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Wash, Nicholas D. "Upwind iteration techniques for compressible flow computations." Thesis, University of Oxford, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.308589.
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Yang, Zhiyan. "Numerical simulation of incompressible and compressible flow." Thesis, University of Sheffield, 1989. http://etheses.whiterose.ac.uk/3485/.
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This thesis describes the development of a numerical solution procedure which is valid for both incompressible flow and compressible flow at any Mach number. Most of the available numerical methods are for incompressible flow or compressible flow only and density is usually chosen as a main dependent variable by almost all the methods developed for compressible flow. This practice limits the range of the applicability of these methods since density changes can be very small when Mach number is low. Even for high Mach number flows the existing time-dependent methods may be inefficient and costly when only the finial steady-state is of concern. The presently developed numerical solution procedure, which is based on the SIMPLE algorithm, solves the steady-state form of the Navier-stokes equations, and pressure is chosen as a main dependent variable since the pressure changes are always relatively larger than the density changes. This choice makes it possible that the same set of variables can be used for both incompressible and compressible flows. It is believed that Reynolds stress models would give better performance in some cases such as recirculating flow, highly swirling flow and so on where the widely used two equation k-e model performs poorly. Hence, a comparative study of a Reynolds stress model and the k-e model has been undertaken to assess their performance in the case of highly swirling flows in vortex throttles. At the same time the relative performance of different wall treatments is also presented. It is generally accepted that no boundary conditions should be specified at the outflow boundary when the outflow is supersonic, and all the variables can be obtained by extrapolation. However, it has been found that this established principle on the outflow boundary conditions is misleading, and at least one variable should be specified at the outflow boundary. It is also shown that the central differencing scheme should be used for the pressure gradient no matter whether it is subsonic or supersonic flow.
12
Suddhoo, A. "Inviscid compressible flow past multi-element aerofoils." Thesis, University of Manchester, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.356714.
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Batten, Paul. "Compressible flow simulation on a parallel computer." Thesis, University of Southampton, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.358770.
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Svedholm, Matheus, and Josefine Gessl. "Laboratory exercise - Compressible flow, oblique shock waves." Thesis, KTH, Skolan för teknikvetenskap (SCI), 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-276595.
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When studying to become an engineer the education is mainly theoretical and to confirm the theory laboratory exercises are incorporated in the curriculum. Being able to visualize the phenomenons studied helps in giving the students a deeper understanding. The purpose of this report is to aid the department of fluid mechanics at KTH in designing an experiment to help the students understand the theory of oblique shock waves. The project is divided in two parts. Part one the design of the wedge and base plate and part two the creation of the actual experiment and lab PM. The design of the wedge is quite simple. It is a sharp wedge with two angles measured from the horizontal plane, 8° at the top and 4° at the bottom, this is so that two measurements can be made per experiment. Writing the PM and the design of the exercise is the main part of this project. The result is a laboratory exercise where the students compare the flow around a wedge in a shock tube for three different Mach numbers, subsonic, transonic and supersonic. Using shadowgraph optics and a high speed camera the image of the shock is captured. The different regimes are then discussed and compared with the help of theoretical calculations and the measured values.Inom ingenjörsutbildningar är utbildningen huvudsakligen teoretisk och för att bekräfta teorin integreras laborationer i läroplanen. Möjligheten att visualisera de studerade fenomenen hjälper studenterna att få en djupare förståelse. Syftet med denna rapport är att hjälpa den strömningsmekaniska avdelningen på KTH att ta fram ett experiment som hjälper studenterna att förstå teorin om sneda stötvågor. Projektet är uppdelat i två delar. Del ett, design av kilen och fästet och del två framtagningen av själva experimentet och lab PMet. Kilens design är ganska simpel. Det är en vass kil med två vinklar mätta från horisontalplanet , 8° på ovansidan och 4° på undersidan, detta så att man kan göra två mätningar per experiment. Utformandet av laborationen och labpeket är huvuddelen av detta projekt. Resultatet är en laboration där studenterna jämför flödet runt en kil i ett stötrör för tre olika machtal, subsoniskt, transoniskt och supersoniskt. Med hjälp av en höghastighetskamera och shadowgraph optik kan stötvågen fångas på bild. De olika scenarierna diskuteras och jämförs med hjälp av teoretiska beräkningar och de uppmätta värdena.
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Abou-Haidar, Nabil Ibrahim. "Compressible flow pressure losses in branched ducts." Thesis, University of Liverpool, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.330238.
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Vilhelmsson, Carl. "Compressible Flow Modeling with Combustion Engine Applications." Thesis, Linköpings universitet, Fordonssystem, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-138434.
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The high demands on low fuel consumption and low emissions on the combustion engines of both today, and the future, is highly dependent on advanced control systems in order to fulfill these demands. The control systems and strategies are based on models which describe the physical system. The more accuratly the models describe the real world system, the more accurate the control will be, leading to better fuel economy and lower emissions. This master's thesis investigates and improves the mass flow model used for a compressible restriction, such as over the throttle valve, EGR valve, or the wastegate valve, for example. The standard model is evaluated and an improvement is proposed which does not assume isentropic flow. This seems to explain the deviation from the isentropic Psi-function shown in earlier research such as (Andersson:2005). Furthermore a throttle valve is analyzed in ANSYS in order to show the generation of entropy. The presence of pressure pulsations in a combustion engine is also evaluated, especially how they effect the otherwise assumed steady flow model. It is tested if a mean value pressure is sufficient or if one needs to take the pulsations in to account, and the result shows that a mean pressure is sufficient, at least for the throttle when typical intake manifold pulsations is present. A dynamic flow model is also derived which can be useful for pressure ratios close to one. The dynamic flow model is based on the standard equation but with an extra dynamic term, however it is not implemented and tested due to complexity and time limitation. The proposed new non-isentropic flow model has proven promising and can hopefully lead to lower emissions and better fuel economy.
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Ravindran, S. S. "Uniqueness theory for compressible flows." Thesis, University of British Columbia, 1991. http://hdl.handle.net/2429/30276.
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This thesis investigates questions of uniqueness in the theory of Compressible flow. First, various uniqueness theorems for compressible flow are reviewed in an expository manner. Roughly, these theorems state that fluid motion in a bounded region Ω = Ω(t) is uniquely determined by its initial data together along with certain boundary conditions. Next, this analysis is extended to magnetohydrodynamic flows and uniqueness theorems are given for a variety of possible cases. The basic question in all these theorems is the determination of appropriate boundary conditions. The proofs are by energy estimates.Science, Faculty of
Mathematics, Department of
Graduate
18
Semlitsch, Bernhard. "Large Eddy Simulation of Turbulent Compressible Jets." Doctoral thesis, KTH, Mekanik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-156230.
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Acoustic noise pollution is an environmental aggressor in everyday life. Aero- dynamically generated noise annoys and was linked with health issues. It may be caused by high-speed turbulent free flows (e.g. aircraft jet exhausts), by airflow interacting with solid surfaces (e.g. fan noise, wind turbine noise), or it may arise within a confined flow environment (e.g. air ventilation systems, refrigeration systems). Hence, reducing the acoustic noise levels would result in a better life quality, where a systematic approach to decrease the acoustic noise radiation is required to guarantee optimal results. Computational predic- tion methods able to provide all the required flow quantities with the desired temporal and spatial resolutions are perfectly suited in such application areas, when supplementing restricted experimental investigations. This thesis focuses on the use of numerical methodologies in compressible flow applications to understand aerodynamically noise generation mechanisms and to assess technologies used to suppress it. Robust and fast steady-state Reynolds Averaged Navier-Stokes (RANS) based formulations are employed for the optimal design process, while the high fidelity Large Eddy Simulation (LES) approach is utilized to reveal the detailed flow physics and to investigate the acoustic noise production mechanisms. The employment of fast methods on a wide range of cases represents a brute-force strategy used to scrutinize the optimization parameter space and to provide general behavioral trends. This in combination with accurate simulations performed for particular condi- tions of interest becomes a very powerful approach. Advance post-processing techniques (i.e. Proper Orthogonal Decomposition and Dynamic Mode Decomposition) have been employed to analyze the intricate, highly turbulent flows. The impact of using fluidic injection inside a convergent-divergent nozzle for acoustic noise suppression is analyzed, first using steady-state RANS simulations. More than 250 cases are investigated for the optimal injection location and angle, amount of injected flow and operating conditions. Based on a-priori established criteria, a few optimal candidate solutions are detected from which one geometrical configuration is selected for being thoroughly investigated by using detailed LES calculations. This allows analyzing the unsteady shock pattern movement and the flow structures resulting with fluidic injec- tion. When investigating external fluidic injection configurations, some lead to a high amplitude shock associated noise, so-called screech tones. Such unsteady phenomena can be captured and explained only by using unsteady simulations. Another complex flow scenario demonstrated using LES is that of a high ve- locity jet ejected into a confined convergent-divergent ejector (i.e. a jet pump). The standing wave pattern developed in the confined channel and captured by LES, significantly alters the acoustic noise production. Steady-state methods failed to predict such events. The unsteady highly resolved simulations proved to be essential for analyzing flow and acoustics phenomena in complex problems. This becomes a very powerful approach when is used together with steady-state, low time-consuming formulations and when complemented with experimental measurements.QC 20141202
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Grigoriev, Igor. "Turbulence modeling of compressible flows with large density variation." Doctoral thesis, KTH, Turbulens, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-183452.
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In this study we highlight the influence of mean dilatation and mean density gradient on the Reynolds stress modeling of compressible, heat-releasing and supercritical turbulent flows.Firstly, the modeling of the rapid pressure-strain correlation has been extended to self-consistently account for the influence of mean dilatation.Secondly, an algebraic model for the turbulent density flux has been developed and coupled to the tensor equationfor Reynolds stress anisotropy via a 'local mean acceleration',a generalization of the buoyancy force. We applied the resulting differential Reynolds stress model (DRSM) and the corresponding explicit algebraic Reynolds stress model (EARSM) to homogeneously sheared and compressed or expanded two-dimensional mean flows. Both formulations have shown that our model preserves the realizability of the turbulence, meaning that the Reynolds stresses do not attain unphysical values, unlike earlier approaches. Comparison with rapid distortion theory (RDT) demonstrated that the DRSM captures the essentials of the transient behaviour of the diagonal anisotropies and gives good predictions of the turbulence kinetic energy. A general three-dimensional solution to the coupled EARSM has been formulated. In the case of turbulent flow in de Laval nozzle we investigated the influence of compressibility effects and demonstrated that the different calibrations lead to different turbulence regimes but with retained realizability. We calibrated our EARSM against a DNS of combustion in a wall-jet flow. Correct predictions of turbulent density fluxes have been achieved and essential features of the anisotropy behaviour have been captured.The proposed calibration keeps the model free of singularities for the cases studied. In addition, we have applied the EARSM to the investigation of supercritical carbon dioxide flow in an annulus. The model correctly captured mean enthalpy, temperature and density as well as the turbulence shear stress. Hence, we consider the model as a useful tool for the analysis of a wide range of compressible flows with large density variation.QC 20160314
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Pishevar, Isfahani Ahmadreza. "High-order computation of unsteady-state compressible flow." Thesis, Imperial College London, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.309226.
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Szemberg, O'Connor Teddy. "Bulk viscosity effects in compressible turbulent Couette flow." Thesis, Imperial College London, 2018. http://hdl.handle.net/10044/1/62657.
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This work investigates the effect of bulk viscosity in one-, two-, and three{dimensional compressible fows via direct numerical simulation. The role of bulk viscosity in compressible turbulence is of increasing importance due to three applications: spacecraft descending through the Martian atmosphere, the thermodynamic cycle of solar-thermal power plant, and carbon capture and storage compressors. All three rely on the accurate description of turbulence in carbon dioxide, a gas with a bulk-to-shear viscosity ratio three orders of magnitude larger than for air. In these applications, invoking Stokes's hypothesis is questioned as the divergence of velocity is non-zero, implying a significant difference between mechanical and thermodynamic pressures. Results of a constantly forced velocity perturbation follow the same trend as that predicted by Landau's acoustic absorption coeffcient for suffciently high Reynolds numbers. Below an optimum Reynolds number, the damping effectiveness reduces by a different mechanism to that of Landau. Maximum damping is achieved at an acoustic Reynolds number equal to unity. Two-dimensional decaying turbulence at the bulk-to-shear viscosity ratio of carbon dioxide demonstrates that the magnitude of the dilatational production term is greatly enhanced and is strongly biased to negative values, reducing the generation of velocity dilatation compared to the zero bulk viscosity case. Compressible Couette flow at two Reynolds numbers and two bulk-to-shear viscosity ratios show minimal changes to mean flow quantities and the main terms of interest in the turbulence kinetic energy budget. Instantaneous views of the dilatational velocity field show that an intermediate range of scales are damped in accordance with Landau's acoustic damping coeffcient. At small scales, however, damping reduces and turbulent patterns are preserved.
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Lakshmi, Narasimhan Krishnan. "Dynamics of turbulent spots in a compressible flow." Thesis, University of Southampton, 2006. https://eprints.soton.ac.uk/47088/.
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Otero, Jr Raul. "Compressible Flow Characterization Using Non-Intrusive Acoustic Measurements." Diss., Virginia Tech, 2017. http://hdl.handle.net/10919/79612.
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Non-intrusive acoustic instruments that measure fluid velocity and temperature have been restricted to low subsonic Mach number applications due to increased complexities associated with acoustic refraction, low signal-to-noise ratios, and a limited range of practical applications. In the current work, the use of acoustics for non-intrusive flow monitoring in compressible flows is explored and a novel sonic anemometry and thermometry (SAT) technique is developed. Using multiple arrangements of SAT equipment, a compressible acoustic tomography technique was also developed to resolve flow non-uniformities. Three validation experiments were used to investigate the novel SAT technique performance, and a fourth validation experiment was used to explore compressible flow tomography capabilities.
In the first experiment, an unheated jet was used to verify that the acoustic technique could measure fluid velocities in high subsonic Mach number flows. The application demonstrated velocity root mean square (RMS) errors of 9 m/s in unheated jet flows up to Mach 0.83. Next, a heated jet facility was used to assess the impact of fluid temperature on measurement accuracy. Using jet Mach numbers up to 0.7 and total temperatures up to 700 K, RMS velocity and static temperature errors up to 8.5 m/s (2.4% of maximum jet velocity) and 23.3 K (3.3% of total temperature) were observed. Finally, the acoustic technique was implemented at the exhaust of a JT15D-1A turbofan engine to investigate technique sensitivity to bypass engine conditions. A mass flow rate and thrust estimation approach was developed and RMS errors of 1.1 kg/s and 200 N were observed in conditions up to an exhaust Mach number of 0.48.
Since modern acoustic tomography techniques require an incompressible flow assumption for velocity detection, advancements were made to extend acoustic tomography methods to compressible flow scenarios for the final experiment. The approach was tested in the heated jet operating at Mach 0.48 and 0.72 (total temperature of 675 K, approximately 2.25 times the ambient) and numerical simulations were used to identify technique sensitivity to input variables and system design. This research marks the first time an acoustic method has been used to estimate compressible flow velocities and temperatures.Ph. D.
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Lebon, Gerard Serge Bruno. "Unstructured finite volume algorithms for compressible multiphase flow." Thesis, University of Greenwich, 2011. http://gala.gre.ac.uk/8077/.
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This research presents novel algorithms for computing flow within an unstructured, collocated, finite volume solver in the presence of non-orthogonality and compressibility in order to extend the range of problems which can be modelled with the University's in-house CFD code: PHYSICA. A new non-orthogonality diffusion correction relaxation parameter has been successfully introduced and tested with benchmarks from the literature. Cases involving geometries meshed with commercial packages have been successfully run with the diffusion correction methods, variable bounding and proper under-relaxation practices. The applicability of a pressure interpolation method has also been tested with these cases. A procedure for solving compressible flow within a finite volume, pressure correction type scheme, has been devised and successfully implemented in different test cases. This method is however prone to numerical diffusion in the presence of shocks, but does work even in the presence of skewed meshes. The method was then tested with the case of an oxygen jet entering a heated furnace, for which experimental data is available for comparison. The method was successful in predicting the axial variables of the jet, and used to develop a turbulence modification model for such jets. The method was finally used to model the deformation of a free surface impinged by a compressible jet, using a novel zonal method called zonal Gas And Liquid Analyser (GALA). Convergence was achieved with the method developed in this research, together with the application of the counter diffusion method to model the moving interface.
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Tsuge, Naoki. "Spherically symmetric flow of the compressible Euler equations." 京都大学 (Kyoto University), 2004. http://hdl.handle.net/2433/147790.
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Yip, C. W. H. "Compressible discharge coefficients of branching flows." Thesis, University of Aberdeen, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.233007.
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A two-dimensional numerical model for compressible branching flow through a slot is described for the purpose of predicting the discharge coefficients of film cooling holes in gas turbine blades. The method employs free-streamline theory and the hodograph transformation. It calculates the area ratio of hole to duct and the contraction coefficient from a set of prescribed boundary conditions. An approximate method for calculating the compressible contraction coefficients is also discussed in the thesis. It employs the incompressible theory previously developed by McNown and Hsu (1951) for the free efflux, the 'compressibility factor' and the flow parameter (Po-Pj)/(Po-P1), where Po, Pj, P1 represent the stagnation pressure, the static pressure of the jet and the static pressure of the approach flow, respectively. The advantages of using this method are the direct input of the area ratio of hole to duct and its speed of calculation. Experimental tests were performed using a specially designed rig in a supersonic wind tunnel. The investigations included sharp-edged slots with three different widths, a single hole and a row of two holes. The approach velocity in terms of the characteristic Mach number ranged from 0.18 to 0.58 and the pressure ratio Po/Pj, ranged from 1.10 to 1.97. Agreement between the experimental data and the theoretical values was good to within the experimental accuracy (typically around +/- 5%) for the slots and the 2-hole configuration. For the 1-hole configuration, less bleed flow than predicted was observed, with the discrepancy varying from 7% to 18%. The latter case is a very severe test of a purely two-dimensional theory. The results for the 2-hole plate suggest that the slot theory can in fact be used to predict the flow through a row of holes with small pitch to diameter ratios.
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Jarrah, Yousef Mohd. "Nonlinear interactions in mixing layers and compressible heated round jets." Diss., The University of Arizona, 1989. http://hdl.handle.net/10150/184652.
Full textAbstract:
The nonlinear interactions between a fundamental instability mode and both its harmonics and the changing mean flow are studied using the weakly nonlinear stability theory of Stuart and Watson, and numerical solutions of coupled nonlinear partial differential equations. The first part of this work focuses on incompressible cold (or isothermal; constant temperature throughout) mixing layers, and for these, the first and second Landau constants are calculated as functions of wavenumber and Reynolds number. It is found that the dominant contribution to the Landau constants arises from the mean flow changes and not from the higher harmonics. In order to establish the range of validity of the weakly nonlinear theory, the weakly nonlinear and numerical solutions are compared and the limitation of each is discussed. At small amplitudes and at low-to-moderate Reynolds numbers, the two results compare well in describing the saturation of the fundamental, the distortion of the mean flow, and the initial stages of vorticity roll-up. At larger amplitudes, the interaction between the fundamental, second harmonic, and the mean flow is strongly nonlinear and the numerical solution predicts flow oscillations, whereas the weakly nonlinear theory yields saturation. Beyond the region of exponential growth, the instability waves evolve into a periodic array of vortices. In the second part of this work, the weakly nonlinear theory is extended to heated (or nonisothermal mean temperature distribution) subsonic round jets where quadratic and cubic nonlinear interactions are present, and the Landau constants also depend on jet temperature ratio, Mach number and azimuthal mode number. Under exponential growth and nonlinear saturation, it is found that heating and compressibility suppress the growth of instability waves, that the first azimuthal mode is the dominant instability mode, and that the weakly nonlinear solution describes the early stages of the roll-up of an axisymmetric shear layer. The receptivity of a typical jet flow to pulse type input disturbances is also studied by solving the initial value problem and then examining the behavior of the long-time solution. The excitation produces a wave packet which consists of a few oscillations and is convected downstream by the mean flow. The magnitude of the disturbance in the jet depends on the location of the excitation and there is an optimum position at which little energy input will produce large perturbations. It is found that in order to generate the largest perturbations at any point in the jet, the disturbance should be deposited into the flow at a point where the phase velocity of the most amplified wave equals the fluid velocity (of the base flow).
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Moragues, Ginard Margarida. "Variational multiscale stabilization and local preconditioning for compressible flow." Doctoral thesis, Universitat Politècnica de Catalunya, 2016. http://hdl.handle.net/10803/384841.
Full textAbstract:
This thesis is about the stabilization of the numerical solution of the Euler and Navier- Stokes equations of compressible flow. When simulating numerically the flow equations, if no stabilization is added, the solution presents non-physical (but numerical) oscillations. For this reason the stabilization of partial differential equations and of the fluid dynamics equations is of great importance. In the framework of the so-called variational multiscale stabilization, we present here a stabilization method for compressible flow. The method assessment is done first of all on a batch of academical examples for different Mach numbers, for viscous and inviscid, steady and transient flow. Afterwards the method is applied to atmospheric flow simulations. To this end we solve the Euler equations for dry and moist atmospheric flow. In the presence of moisture a set of transport equations for water species should be solved as well. This domain of application is a real challenge from the stabilization point of view because the correct amount of stabilization must be added in order to preserve the physical properties of the atmospheric flow. At this point, in order to even improve our method, we turn towards local preconditioning. Local preconditiong permits to reduce the stiffness problems that present the flow equations and cause a bad and slow convergence to the solution. With this purpose in mind we combine our stabilization method with local preconditioning and present a stabilization method for the preconditioned Navier-Stokes equations of compressible flow, that we call P-VMS. This method is tested over several examples at different Mach numbers and proves a significant improvement not only in the convergence to the solution but also in the accuracy and robustness of the method. Finally, the benefits of P-VMS are theoretically assessed using Fourier stability analysis. As a result of this analysis a modification on the computation of the time step is done even improving the convergence of the method.Aquesta tesi tracta sobre l'estabilització de la solució numèrica de les equacions d'Euler i Navier-Stokes de flux compressible. Quan es simulen numèricament les equacions que governen els fluids, si no s'afegeix cap estabilització, la solució presenta oscil·lacions no físiques sinó numèriques. Per aquest motiu l'estabilització de les equacions en derivades parcials i de les equacions de la mecànica de fluids és de gran importància. Dins del marc de l'anomenada estabilització de multiescales variacionals, presentem aquí un mètode d'estabilització per flux compressible. L'evaluació del mètode es realitza primer en varis exemples acadèmics per diferents nombres de Mach, per flux viscós, inviscid, estacionari i transitori. Després el mètode s'aplica a simulacions de flux atmosfèric. Per això, resolem les equacions d'Euler per flux atmosfèric sec i humit. En presència d'humitat, també s'ha de resoldre un grup d'equacions de transport d'espècies d'aigua. Aquest domini d'aplicació representa un desafiament des del punt de vista de l'estabilització, donat que s'ha d'afegir la quantitat adequada d'estabilització per tal de preservar les propietats físiques del flux atmosfèric. Arribat aquest punt, per tal de millorar el nostre mètode, ens interessem pels precondicionadors locals. Els precondicionadors locals permeten reduir els problemes de rigidesa que presenten les equacions dels fluids i que són causa d'una pitjor i més lenta convergència cap a la solució. Amb aquest propòsit en ment, combinem el nostre mètode d'estabilització amb els precondicionadors locals i presentem un mètode d'estabilització per les equacions de Navier-Stokes de flux compressible, anomenem aquest màtode P-VMS. Aquest mètode es evaluat per mitjà de varis exemples per diferents nombres de Mach i demostra una millora sustancial no només pel que fa la convergència cap a la solució, sinó també en la precisió i robusteza del mètode. Finalment els beneficis del P-VMS es demostren teòricament a través de l'anàlisi d'estabilitat de Fourier. Com a resultat d'aquest anàlisi, sorgeix una modificació en el càlcul del pas de temps que millora un cop més la convergència del mètode
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Badcock, Kenneth John. "Application of numerical methods to transient compressible fluid flow." Thesis, University of Oxford, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.306540.
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Venditti, David Anthony 1973. "Grid adaptation for functional outputs of compressible flow simulations." Thesis, Massachusetts Institute of Technology, 2002. http://hdl.handle.net/1721.1/29246.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2002.Includes bibliographical references (p. 143-150).
An error correction and grid adaptive method is presented for improving the accuracy of functional outputs of compressible flow simulations. The procedure is based on an adjoint formulation in which the estimated error in the functional can be directly related to the local residual errors of both the primal and adjoint solutions. This relationship allows local error contributions to be used as indicators in a grid adaptive method designed to produce specially tuned grids for accurately estimating the chosen functional. The method is applied to two-dimensional inviscid and viscous (laminar) flows using standard finite volume discretizations, and to scalar convection-diffusion using a Galerkin finite element discretization. Isotropic h-refinement is used to iteratively improve the grids in a series of subsonic, transonic, and supersonic inviscid test cases. A commonly-used adaptive method that employs a curvature sensor based on measures of the local interpolation error in the solution is implemented to comparatively assess the performance of the proposed output-based procedure. In many cases, the curvature-based method fails to terminate or produces erroneous values for the functional at termination. In all test cases, the proposed output-based method succeeds in terminating once the prescribed accuracy level has been achieved for the chosen functional.
(cont.) Output-based adaptive criteria are incorporated into an anisotropic grid-adaptive procedure for laminar Navier-Stokes simulations. The proposed method can be viewed as a merging of Hessian-based adaptation with output error control. A series of airfoil test cases are presented for Reynolds numbers ranging from 5,000 to 100,000. The proposed adaptive method is shown to compare very favorably in terms of output accuracy and computational efficiency relative to pure Hessian-based adaptation.
by David Anthony Venditti.
Ph.D.
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Reu, Taekyu. "Techniques for compressible flow calculations on multi-zone grids." Diss., Virginia Polytechnic Institute and State University, 1988. http://hdl.handle.net/10919/52327.
Full textAbstract:
In order to simulate inviscid/viscous compressible flowfields about 3-D realistic aerodynamic bodies, the combined use of an implicit, upwind biased real gas scheme with 3-D fully conservative patched grid techniques is discussed. An "equivalent" gamma formulation is implemented in order to model real gas effects in Van Leer's flux vector splitting (FVS) and Roe’s flux difference splitting (FDS) scheme. A hybrid approximate-factorization (AF)/relaxation algorithm is used as an efficient solver of the Euler, parabolized Navier-Stokes, and thin-layer Navier-Stokes equations. Two different approaches, clipping and Ramshaw’s rezoning algorithms, for performing a conservative flux calculation are described and compared in terms of numerical efficiency. In order to show the real gas \\\ effects in the upwind schemes, two tcst problems are solved. Also to demonstrate the capability of the patched grid approach, the turbulent flowüeld about 3-D analytic forebody is calculated as another test problem. Due to the poor results of the Baldwin-Lomax turbulent model for separated flows, only the attached flowtield is considered in the analytic forebody calculation. Finally, as applications of this approach, the inviscid/viscous flowfields about several aerodynamic bodies are calculated including a generic hypersonic aircraft, a model of the SR-71 aircraft, and F-18 forebody with strakes.Ph. D.
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Baghaei, Masoud. "Research on fluidic oscillators under incompressible and compressible flow conditions." Doctoral thesis, Universitat Politècnica de Catalunya, 2020. http://hdl.handle.net/10803/669607.
Full textAbstract:
One of the main advantages of fluidic oscillators is that they do not have moving parts, which brings high reliability whenever being used in real applications. To use these devices in real applications, it is necessary to evaluate their performance, since each application requires a particular injected fluid momentum and frequency. In this PhD., the performance of a given fluidic oscillator is evaluated at different Reynolds numbers via a 3D-computational fluid dynamics (CFD) analysis under incompressible and compressible flow conditions. In the first stage, the net momentum applied to the incoming jet is compared with the dynamic maximum stagnation pressure in the mixing chamber, to the dynamic output mass flow, to the dynamic feedback channels mass flow, to the pressure acting to both feedback channels outlets, and to the mixing chamber inlet jet oscillation angle. A perfect correlation between these parameters is obtained, therefore indicating the oscillation is triggered by the pressure momentum term applied to the jet at the feedback channels outlets. The stagnation pressure fluctuations appearing at the mixing chamber inclined walls are responsible for the pressure momentum term acting at the feedback channels outlets, thus it is proved that the oscillations are pressure-driven. In the second stage, several performance parameters were numerically evaluated as a function of different internal modifications via using 3D-CFD simulations. The evaluation is based on studying the output mass flow frequency and amplitude whenever several internal geometry parameters are modified. The geometry modifications considered were the mixing chamber inlet and outlet widths, and the mixing chamber inlet and outlet wall inclination angles. The concept behind this is, to evaluate how much the fluidic oscillator internal dimensions affect the device's main characteristics, and to analyze which parts of the oscillator produce a higher impact on the fluidic oscillator output characteristics. For the different internal modifications, evaluated, special care is taken in studying the forces required to flip the jet. The entire study is performed for three different Reynolds numbers, 8711, 16034 and 32068. Among the conclusions reached it is to be highlighted that, for a given Reynolds number, modifying the internal shape affects the oscillation frequencies and amplitudes. Any oscillator internal modification generates a much relevant effect as Reynolds number increases. Under all conditions studied, it was observed that the fluidic oscillator is pressure-driven under incompressible flow conditions as discussed in the first and second stages. In the third stage, the feedback channel effect on the oscillator output mass flow frequency and amplitude under compressible flow conditions were evaluated. In order to bring light to this point, a set of three dimensional Direct Numerical Simulations under compressible flow conditions, are introduced in the present stage, four different feedback channel lengths and two inlet fluid velocities are considered. From the results obtained, it was observed that as the inlet velocity increases, the fluidic oscillator output mass flow frequency and amplitude increase. An increase of the feedback channel length decreases the output mass flow oscillating frequency. At high feedback channel lengths, the form of the main oscillation tends to disappear, the jet inside the mixing chamber simply actuates at high frequencies, for these cases, the mass flow and pressure signals are very scattered due to the pressure waves appearing on mixing chamber converging surfaces and both feedback channels at the same time. Once the FC length exceeds a certain threshold, the oscillation stops. Under compressible conditions, the oscillations are pressure-driven as previously stated for the incompressible cases. The forces due to the pressure are much stronger than the mass flow flowing along the feedback channels.El principal avantatge dels oscil·ladors fluídics es que no te parts mòbils, i això fa que sigui més fiable en aplicacions reals. Per tal d'aplicar aquests oscil·ladors en un cas concret, es necessari avaluar el seu comportament, doncs cada cas concret necessita una freqüència i quantitat de moviment donades. En el present doctorat s'ha analitzat mitjançant 3D-CFD, una configuració de oscil·lador fluídic per diferents números de Reynolds, diferents geometries internes i considerant el fluid com incompressible i compressible. Inicialment, la quantitat de moviment aplicada al jet entrant a la cambra de barreja, es comparada amb la pressió d'estancament dinàmica a les parets convergents de la cambra de barreja, amb el cabal màssic dinàmic que surt del actuador, amb el cabal màssic dinàmic que passa per els canals de realimentació, amb la pressió dinàmica que hi ha a la sortida dels canals de realimentació i amb el angle de oscil·lació del jet a l'entrada de la cambra de barreja. Tots aquests paràmetres es va veure que estaven correlacionats i això indicava que el origen de les oscil·lacions del jet era únic i era la pressió d'estancament a les parets convergents de la cambra de barreja, provant que les oscil·lacions son dirigides per gradients de pressió. Posteriorment es va fer el mateix tipus de estudi però modificant la amplada i angle de inclinació a l'entrada de la cambra de barreja i també modificant la amplada i angle de inclinació de les parets de sortida de la cambra de barreja. Aquestes quatre modificacions de la geometria interna es van fer per tres números de Reynolds diferents, 8711, 16034 i 32068. Entre les conclusions obtingudes cal destacar que, la freqüència i amplitud de oscil·lació del jet a la sortida del actuador pot ser modificada al variar les dimensions i angles interns de la cambra de barreja. Independentment del número de Reynolds estudiat i de la modificació interna considerada, es va comprovar que les oscil·lacions estaven dirigides per els gradients de pressió existents entre les dos sortides dels conductes de realimentació. L'efecte generat per qualsevol modificació interna era sempre més rellevant a números de Reynolds alts. En la tercera fase de la tesi el fluid es va considerar com a compressible subsònic, i es va avaluar els efectes de la modificació de la longitud dels canals de realimentació, sobre la freqüència i amplitud del flux que surt del oscil·lador. Quatre diferents longituds i dos números de Mach van ser avaluats. Al augmentar la longitud del canal de realimentació, la freqüència i amplitud de la oscil·lació disminueix, la oscil·lació tendeix a ser mes caòtica, apareixen altes freqüències que fan que el jet fluctuï en lloc de oscil·lar, de fet a partir de una certa longitud les oscil·lacions desapareixen i només hi han fluctuacions. Aquestes fluctuacions apareixen abans per elevats números de Mach. Les oscil·lacions son degudes a gradients de pressió, al igual que en el cas de fluid incompressible. De fet, per fluid compressible, el cabal màssic que passa per els canals de realimentació, juga un paper menys rellevant que en el cas de fluid incompressible.
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Mack, Christoph. "Global stability of compressible flow about a swept parabolic body." Phd thesis, Ecole Polytechnique X, 2009. http://pastel.archives-ouvertes.fr/pastel-00005752.
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Javareshkian, Mohammad Hassan. "High resolution difference schemes for steady and transient compressible flow." Thesis, Imperial College London, 1996. http://hdl.handle.net/10044/1/7186.
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Issman, Emmanuel. "Implicit solution strategies for compressible flow equations on unstructured meshes." Doctoral thesis, Universite Libre de Bruxelles, 1997. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/212181.
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Suratanakavikul, Varangrat. "Computational study of compressible flow in an S-shaped duct." Thesis, Imperial College London, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.313370.
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Pierce, Niles A. "Preconditioned multigrid methods for compressible flow calculations on stretched meshes." Thesis, University of Oxford, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.362030.
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RONZANI, ERNESTO RIBEIRO. "NUMERICAL SOLUTION OF COMPRESSIBLE AND INCOMPRESSIBLE FLOW IN IRREGULAR GEOMETRIES." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 1996. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=18648@1.
Full textAbstract:
CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOEste trabalho propõe um método numérico de solução de escoamentos de fluidos compressíveis e incompressíveis a qualquer número de Mach em geometrias irregulares. Um sistema bidimensional de coordenadas curvilíneas não-ortogonais,coincidentes com os contornos físicos é utilizado. Os componentes cartesianos de velocidade são usados nas equações da quantidade de movimento e os covariantes na equação da continuidade. Seleciona-se a técnica de volumes finitos para discretizar as equações de conservação relacionadas aos princípios físicos, em regime permanente devido esta preservar a propriedade conservativa das equações e a sua con sistência física no processo numérico. Adota-se a configuração de malha co-localizada, avaliando-se todas as variáveis dependentes nos pontos centrais dos volumes são avaliados com esquemas Power-Law e Quick. Especial atenção é dada ao tratamento numérico das condições de contorno. O problema do acoplamento massa específica-pressão-velocidade é solucionado usando-se uma combinação das equações da continuidade, de quantidade de movimento linear e de uma equação de estado, gerando duas equações de correção da pressão. A primeira corrige a massa específica e a pressão, a segunda, o fluxo de massa e a velocidade. Propõe-se uma modificação da equação da correção da velocidade usando um termo de compensação do erro obtido na sua avaliação a fim de acelerar a convergência. Utilizam-se vários tipos de interpolação da massa específica na face, para minimizar as atenuações das variáveis, causadas pela falsa difusão. Para a solução das equações algébricas resultantes usa-se o algoritmo TDMA linha por linha e um processo de correção por blocos para acelerar a convergência. O método proposto é verificado em seis problemas testes, através da comparação com os resultados analíticos e numéricos disponíveis na literatura.
The present work consists in the development of a numerical method of solution of compressible and incompressible fluid flow for all speed in iregular geometries. A boundary-fitted two-dimensional nonorthogonal curvilinear coordinate systeam is utilized. The cartesian velocity components are the dependent variables in the momentum equations and covariant velocity components are used in the continuity equation. The finite-volume technique was selected to discretuze the steady-state physical phenomenon conservation equations, since this method keeps the conservative property of the equations and its physical consistency in the numerical process. A nonstaggered grid was employed, and all dependent variables are evaluated at the cell center points, which divides the physical domain. The convection-diffusion fluxes at the control volumes faces are evaluated with the Power Law and Quick shemes. Special attention is paid to the numerical treatment of boundary conditions. The problem of velocity-pressure-density coupling is solved using a combination of continuity, momentum equations and state equation resulting in two pressure correction equations. The first equation corrects the density and the pressure, the second equation corrects the mass flux and the velocity. A modification in the velocity correction equations is proposed using a compensationterm to accelerate the convergence. Several types of interpolation of the face density are used to reduce variable atenuations, caused by false diffusion. For the solution of the resulting algebric equations,the line-by-line TDMA algorith is used as well as a block-correction method to accelerate the convergence. The proposed method is verified on six test problems,by comparing the present results with analytical and numerical results avaiable in the literature.
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Naigle, Shawn Christopher. "Flow Control of Compressible Dynamic Stall using Vortex Generator Jets." The Ohio State University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=osu1460931112.
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Kupiainen, Marco. "Compressible Turbulent Flows : LES and Embedded Boundary Methods." Doctoral thesis, KTH, Numerisk analys, NA, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-10090.
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Sankaran, Vaidyanathan. "Sub-grid Combustion Modeling for Compressible Two-Phase Flows." Diss., Georgia Institute of Technology, 2003. http://hdl.handle.net/1853/5274.
Full textAbstract:
A generic formulation for modeling the sub-grid combustion in
compressible, high Reynolds number, two-phase, reacting flows has
been developed and validated. A sub-grid mixing/combustion model
called Linear Eddy Mixing (LEM) model has been extended to
compressible flows and used inside the framework of Large Eddy
Simulation (LES) in this LES-LEM approach. The LES-LEM approach is
based on the proposition that the basic mechanistic distinction
between the convective and the molecular effects should be
preserved for accurate prediction of the complex flow-fields such
as those encountered in many combustion systems. In LES-LEM, all
the physical processes such as molecular diffusion, small and
large scale turbulent convection and chemical reaction are modeled
separately but concurrently at their respective time scales. This
multi-scale phenomena is solved using a two-scale numerical
approach, wherein molecular diffusion, small scale turbulent
convection and chemical reaction are grouped as small scale
processes and the convection at the (LES grid) resolved scales are
deemed as the large scale processes. Small-scale processes are
solved using a hybrid finite-difference Monte-carlo type approach
in a one-dimensional domain. Large-scale advection on the
three-dimensional LES grid is modeled in a Lagrangian manner that
conserves mass.
Liquid droplets (represented by computational parcels) are tracked
using the Lagrangian approach wherein the Newton's equation of
motion for the discrete particles are integrated explicitly in the
Eulerian gas field.
Drag effects due to the droplets on the gas phase and the heat
transfer between the gas and the liquid phase are explicitly
included. Thus, full coupling is achieved between the two phases
in the simulation.
Validation of the compressible LES-LEM approach is conducted by
simulating the flow-field in an operational General Electric
Power Systems' combustor (LM6000). The results predicted using
the proposed approach compares well with the experiments and a
conventional (G-equation) thin-flame model.
Particle tracking algorithms used in the present study are
validated by simulating droplet laden temporal mixing layers.
Comparison of the energy growth in the fundamental and
sub-harmonic mode in the presence and absence of the droplets
shows excellent agreement with spectral DNS.
Finally, to test the ability of the present two-phase LES-LEM in
simulating partially premixed combustion, a LES of freely
propagating partially premixed flame in a droplet-laden isotropic
turbulent field is conducted. LES-LEM along with the spray models
correctly captures the flame structure in the partially premixed
flames. It was found that most of the fuel droplets completely
vaporize before reaching the flame, and hence provides a
continuous supply of reactants, which results in an intense
reaction zone similar to a premixed flame. Some of the droplets
that did not evaporate completely, traverse through the flame and
vaporize suddenly in the post flame zone. Due to the strong
spatial variation of equivalence ratio a broad flame similar to a
premixed flame is realized. Triple flame structure are also
observed in the flow-field due to the equivalence ratio
fluctuations.
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Wadey, Philip David. "Goetler vortex instabilities of incompressible and compressible boundary layers." Thesis, University of Exeter, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.253560.
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Turkbeyler, Erdal. "Computation of multi-dimensional inviscid transonic flow." Thesis, Imperial College London, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.265983.
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Lin, C. A. "Computational study of compressibility effects in two-dimensional steady turbulent junction flow at high subsonic mach numbers." Thesis, University of Manchester, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.380181.
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Otero, Evelyn. "Acceleration of Compressible Flow Simulations with Edge using Implicit Time Stepping." Licentiate thesis, KTH, Aerodynamik, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-97455.
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Computational fluid dynamics (CFD) has become a significant tool routinely used in design and optimization in aerospace industry. Typical flows may be characterized by high-speed and compressible flow features and, in many cases, by massive flow separation and unsteadiness. Accurate and efficient numerical solution of time-dependent problems is hence required, and the efficiency of standard dual-time stepping methods used for unsteady flows in many CFD codes has been found inadequate for large-scale industrial problems. This has motivated the present work, in which major effort is made to replace the explicit relaxation methods with implicit time integration schemes. The CFD flow solver considered in this work is Edge, a node-based solver for unstructured grids based on a dual, edge-based formulation. Edge is the Swedish national CFD tool for computing compressible flow, used at the Swedish aircraft manufacturer SAAB, and developed at FOI, lately in collaboration with external national and international partners. The work is initially devoted to the implementation of an implicit Lower-Upper Symmetric Gauss-Seidel (LU-SGS) type of relaxation in Edge with the purpose to speed up the convergence to steady state. The convergence of LU-SGS has been firstly accelerated by basing the implicit operator on a flux splitting method of matrix dissipation type. An increase of the diagonal dominance of the system matrix was the principal motivation. Then the code has been optimized by means of performance tools Intel Vtune and CrayPAT, improving the run time. It was found that the ordering of the unknowns significantly influences the convergence. Thus, different ordering techniques have been investigated. Finding the optimal ordering method is a very hard problem and the results obtained are mostly illustrative. Finally, to improve convergence speed on the stretched computational grids used for boundary layers LU-SGS has been combined with the line-implicit method.QC 20120626
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Taghizadeh, Manzari M. "An unstructured grid finite element algorithm for compressible turbulent flow computations." Thesis, Swansea University, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.639151.
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This work describes the design and implementation of an algorithm for solving the compressible turbulent flow equations, in two-dimensional space, using two-equation turbulence models. The basic governing equations of the fluid flow are presented and the transport equations for the turbulence kinetic energy and dissipation energy are given for both the k-epsilon and the k-omega models. Some basic physical concepts of turbulence are explained and several different versions of both the k-epsilon and the k-omega models are considered. The principle of upwind discretisation is discussed and some physical and mathematical aspects of the Euler equations are presented. Roe's flux-difference splitting scheme and the ideas behind a MUSCL higher-order extension are introduced. A brief discussion is also included on the concept of limiting. The finite element formulation employed in solving the governing equations is presented and some numerical issues regarding boundary conditions, time integration and robustness are discussed. Several test cases are solved and the effects of the limiters, mesh resolution, shock-boundary layer and shock-shock interactions and turbulence models are studied. Finally, some conclusions are drawn and a few guidelines for future research are presented.
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Otero, Evelyn. "Acceleration of Compressible Flow Simulations with Edge Using Implicit Time Stepping." Doctoral thesis, KTH, Aerodynamik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-156414.
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Computational fluid dynamics (CFD) is a significant tool routinely used indesign and optimization in aerospace industry. Often cases with unsteadyflows must be computed, and the long compute times of standard methods hasmotivated the present work on new implicit methods to replace the standardexplicit schemes. The implementation and numerical experiments were donewith the Swedish national flow solver Edge, developed by FOI,universities, and collaboration partners.The work is concentrated on a Lower-Upper Symmetric Gauss-Seidel (LU-SGS)type of time stepping. For the very anisotropic grids needed forReynolds-Averaged Navier-Stokes (RANS) computations of turbulent boundary layers,LU-SGS is combined with a line-implicit technique. The inviscid flux Jacobians which contribute to the diagonalblocks of the system matrix are based on a flux splitting method with upwind type dissipation giving control over diagonal dominance and artificial dissipation.The method is controlled by several parameters, and comprehensivenumerical experiments were carried out to identify their influence andinteraction so that close to optimal values can be suggested. As an example,the optimal number of iterations carried out in a time-step increases with increased resolution of the computational grid.The numbering of the unknowns is important, and the numberings produced by mesh generators of Delaunay- and advancing front-type wereamong the best.The solver has been parallelized with the Message Passing Interface (MPI) for runs on multi-processor hardware,and its performance scales with the number of processors at least asefficiently as the explicit methods. The new method saves typicallybetween 50 and 80 percent of the runtime, depending on the case, andthe largest computations have reached 110M grid nodes. Theclassical multigrid acceleration for 3D RANS simulations was foundineffective in the cases tested in combination with the LU-SGS solverusing optimal parameters. Finally, preliminary time-accurate simulations for unsteady flows have shown promising results.QC 20141201
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Wixcey, J. R. "Stationary principles and adaptive finite elements for compressible flow in ducts." Thesis, University of Reading, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.253759.
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Rasolonjanahary, Irina. "Wave propagation in pipes of slowly-varying radius with compressible flow." Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/277876.
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The work presented in this thesis studies acoustic perturbations in slowly varying pipes. The slow variation is introduced in the form of a small parameter ${\epsilon}$ and through this in turn gives rise to a slow axial scale $X$ such that $X = {\epsilon}x$ where $x$ is the normal axial coordinate. This allows an asymptotic approach and the WKB method is used to solve the subsequent mathematical problems. The first deals with the existence of a trapped mode in a hard-walled pipe of varying radius conveying fluid. For the derived leading order propagating mode solution, its amplitude becomes singular at transition points $X_{t}$ and $X_{t'}$ where $X_{t} > 0$ and $X_{t'} < 0$ and thus is unable to propagate past these points. Because of the break down in the solution, this leads to the theory that in the neighbourhood of these points there exists a boundary layer in which the original assumption about having slow variation does not hold. By first seeking the thickness of the layer, valid solutions can then be derived and then matched to the outer solutions in order to produce a uniform solution which holds for the entire axial domain. Once this is achieved, it is then used to derive trapped mode solutions. In this case, the theory used is that of two single turning points which are then combined to obtain the full solution. It is illustrated through consideration of examples and the dependence on ${\epsilon}$ is also shown through various plots. This problem will be considered for a symmetric and asymmetric duct and for differing duct parameters. Problems may arise when the two turning points lie close together and so we seek to improve on the method used by deriving a solution to trapped modes encompassing both turning points, which will be proposed together with some illustrations in order to justify its use and reliability. Next, the case of mode propagations on a thin elastic shell of varying radius conveying fluid is studied. The acoustic solutions of a straight shell in vacuo are first briefly reviewed and then built up by the addition of radius variation and the presence of a stationary fluid. The work presented first outlines the analysis for wave propagation in a slowly-varying thin elastic shell in vacuo. It is found that the shell and the fluid terms are coupled through the fluid pressure term, which is added to the equation governing the radial shell displacements since the pressure is assumed to affect radial motion only. Once the newly corrected equation for the radial shell displacements has been obtained, together with the axial and azimuthal displacements equations, this new system of governing equations is then separated into leading order ${\epsilon}^{0}$ and first order ${\epsilon}^{1}$ systems. In order to simplify the calculations, only the zeroth azimuthal order $m = 0$ will be studied here. With this simplification, a notable result is that the solutions of the torsional motion is decoupled from the axial and radial solutions. Once the dispersion equation is extracted from the leading order system, it can be seen that the axial and radial solutions are in fact coupled. The solution to the in vacuo with varying radius problem is first briefly presented and it is then followed by the solution to the fluid inclusion problem with varying radius, which makes up the main part of this section. The solution is studied for various frequencies and at various points along the shell. In addition, the axial and radial components of the first three modes are examined along with their amplitudes and energy distributions. Finally, mean flow is added and the same analysis is carried out, paying particular attention to the differences which arise in comparison to the stationary flow case.
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Romero, Gonzalez Nicolas. "Design and optimisation of power fluidic components for compressible flow control." Thesis, University of Sheffield, 2014. http://etheses.whiterose.ac.uk/8789/.
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