For the qualification and validation of two-phase CFD-models for medium and large-scale industrial applications dedicated experiments providing data with high temporal and spatial resolution are required. Fluid dynamic parameter like gas volume fraction, bubble size distribution, velocity or turbulent kinetic energy should be measured locally. Considering the fact, that the used measurement techniques should not affect the flow characteristics, radiation based tomographic methods are the favourite candidate for such measurements. Here the recently developed ultrafast X-ray tomography, is applied to measure the local and temporal gas volume fraction distribution in a vertical pipe. To obtain the required frame rate a rotating X-ray source by a massless electron beam and a static detector ring are used. Experiments on a vertical pipe are well suited for development and validation of closure models for two-phase flows. While vertical pipe flows are axially symmetrically, the boundary conditions are well defined. The evolution of the flow along the pipe can be investigated as well. This report documents the experiments done for co-current upwards and downwards air-water and steam-water flows as well as for counter-current air-water flows. The details of the setup, measuring technique and data evaluation are given. The report also includes a discussion on selected results obtained and on uncertainties.

The interest of how small non-spherical particles transport behaviour when transported in pipe-flow is of large interest in a variety applications. This kind of theory have been used when studying composite manufacturing and how particles behaves in the human lungs. The main focus is to study the statistical deposition rate in a flow-field with and without capillary action and gravity. Two kind of particle shapes are of main interest which are prolate and oblate spheroids. In this study the method of vector projection is used to track particle orientation instead of the more common methods of Euler-angles or quaternions. The method of tracking the particle motion used is Lagrangian tracking method which solves the equations of motion for the particles individually. When studying particles of nano-scale the importance of the phenomenon called Brownian motion arises. The inclusion if the Brownian motion gives rise to the solving of stochastic differential equations for the particle transport. To solve the resulting equations of transport a MATLAB program was developed to using the numerical Euler-Maruyama scheme. Simulations is done with a large amount of particles with a varying particle size and aspect ratio. The deposition results are compared between the different particles shape and sizes. It is seen that the effect of the Brownian motion on particle deposition rate increases with a smaller particle size. It is also concluded that the Brownian motion is the dominating reason for particle deposition. From comparing particle shape and size it is seen to have a major effect of the particles deposition. Including capillary action or gravity the inclusion doesn't affect particles deposition as much.

Techniques that can increase the SI- engine efficiency while keeping the emissions very low is to reduce the engine displacement volume combined with a charging system. Advanced systems are needed for an effective boosting of the engine and today 1D engine simulation tools are often used for their optimization. This thesis concerns 1D engine simulation of a turbocharged SI engine and the introduction of CFD computations on components as a way to assess inaccuracies in the 1D model. 1D engine simulations have been performed on a turbocharged SI engine and the results have been validated by on-engine measurements in test cell. The operating points considered have been in the engine’s low speed and load region, with the turbocharger’s waste-gate closed. The instantaneous on-engine turbine efficiency was calculated for two different turbochargers based on high frequency measurements in test cell. Unfortunately the instantaneous mass flow rates and temperatures directly upstream and downstream of the turbine could not be measured and simulated values from the calibrated engine model were used. The on-engine turbine efficiency was compared with the efficiency computed by the 1D code using steady flow data to describe the turbine performance. The results show that the on-engine turbine efficiency shows a hysteretic effect over the exhaust pulse so that the discrepancy between measured and quasi-steady values increases for decreasing mass flow rate after a pulse peak. Flow modeling in pipe geometries that can be representative to those of an exhaust manifold, single bent pipes and double bent pipes and also the outer runners of an exhaust manifold, have been computed in both 1D and 3D under steady and pulsating flow conditions. The results have been compared in terms of pressure losses. The results show that calculated pressure gradient for a straight pipe under steady flow is similar using either 1D or 3D computations. The calculated pressure drop over a bend is clearly higher1D engine simulations of turbocharged engines are difficult to using 1D computations compared to 3D computations, both for steady and pulsating flow. Also, the slow decay of the secondary flow structure that develops over a bend, gives a higher pressure gradient in the 3D calculations compared to the 1D calculation in the straight pipe parts downstream of a bend. / QC 20101119

This project aimed to investigate the capability of the STAR CCM+ software when predicting the flow with particles using Lagrangian Particle Tracking and Discrete Element Method. The first part pertained to rectangular channel flow, with ratio between height of the channel and particle diameter (2h/Dp ) of 15. It was found out that simulations of particles in a channel come with many diculties. Such as, obtaining accurate pressure drop results using DEM when comparing to DNS simulations including particles within a reasonable computational time. The second part consisted of a simulation of the off-centred mixing tank. As the use of DEM caused numerical issues, another modeling approach was used. Therefore, the Lagrangian Particle Tracking was used. The outcome of the project is the sensitivity study of the forces which can be applied to the particles. The finding was that the Shear Lift force and the Virtual Mass force have a negligible contribution in regards to the particles distribution. In addition to this, it was also discovered that the turbulence model has a large effect on the particles in the near-wall region. Choosing an isotropic turbulence model resulted in clustering of the particles near the wall, therefore an anisotorpic turbulence model needed to be used.

This thesis presents results of an experimental investigation that characterizes the wall vibration of a pipe with turbulent flow passing through it. Specifically, experiments were conducted using a water flow loop to address three general phenomena. The topics of investigation were: 1) How does the pipe wall vibration depend on the average flow speed, pipe diameter, and pipe thickness for an unsupported pipe? 2) How does the behavior change if the pipe is clamp supported at various clamping lengths? 3) What influence does turbulence generation caused by holed baffle plates exert on the pipe response? A single pipe material (PVC) was used with a range of internal diameters from 5.08 cm to 10.16 cm and diameter to thickness ratios ranging from 8.90 to 16.94. The average flow speed that the experiments were conducted at ranged from 0 to 11.5 m/s. Pipe vibrations were characterized by accelerometers mounted on the pipe wall at several locations along the pipe length. Rms values of the pipe wall acceleration and velocity time series were measured at various flow speeds. Power spectral densities of the accelerometer data were computed and analyzed. Concurrent wall pressure fluctuation measurements were also obtained. The results show that for a fully developed turbulent flow, the rms of the wall pressure fluctuations is proportional to the rms of the wall acceleration and each scale nominally as the square of the average fluid velocity. Also, the rms of the pipe wall acceleration increases with decreasing pipe wall thickness. When changes were made in the pipe support length, it was observed that, in general, pipe support length exercises little influence on the pipe wall acceleration. The influence of pipe support length on the pipe wall velocity is much more pronounced. A non-dimensional parameter describing the pipe wall acceleration is defined and its dependence on relevant independent non-dimensional parameters is presented. Turbulence was induced using baffle plates with various sizes (2.54 cm to 0.159 cm) and numbers of holes drilled through them to provide a constant through area of 35.48 cm2 for each plate. Cavitation exists at high speeds for the largest holed baffle plates and this significantly increases the rms of the pipe wall acceleration. As the baffle plate hole size decreases, vibration levels were observed to return to levels that were observed when no baffle plate was employed. Power spectral densities of the accelerometer data from each baffle plate scenario were also computed and analyzed.

No description available.

Non-pulsatile and pulsatile flow in bent pipes and radial turbine has been assessed with numerical simulations. The flow field in a single bent pipe has been computed with different turbulence modelling approaches. A comparison with measured data shows that Implicit Large Eddy Simulation (ILES) gives the best agreement in terms of mean flow quantities. All computations with the different turbulence models qualitatively capture the so called Dean vortices. The Dean vortices are a pair of counter-rotating vortices that are created in the bend, due to inertial effects in combination with a radial pressure gradient. The pulsatile flow in a double bent pipe has also been considered. In the first bend, the Dean vortices are formed and in the second bend a swirling motion is created, which will together with the Dean vortices create a complex flow field downstream of the second bend. The strength of these structures will vary with the amplitude of the axial flow. For pulsatile flow, a phase shift between the velocity and the pressure occurs and the phase shift is not constant during the pulse depending on the balance between the different terms in the Navier- Stokes equations. The performance of a radial turbocharger turbine working under both non-pulsatile and pulsatile flow conditions has also been investigated by using ILES. To assess the effect of pulsatile inflow conditions on the turbine performance, three different cases have been considered with different frequencies and amplitude of the mass flow pulse and different rotational speeds of the turbine wheel. The results show that the turbine cannot be treated as being quasi-stationary; for example, the shaft power varies with varying frequency of the pulses for the same amplitude of mass flow. The pulsatile flow also implies that the incidence angle of the flow into the turbine wheel varies during the pulse. For the worst case, the relative incidence angle varies from approximately −80° to +60°. A phase shift between the pressure and the mass flow at the inlet and the shaft torque also occurs. This phase shift increases with increasing frequency, which affects the accuracy of the results from 1-D models based on turbine maps measured under non-pulsatile conditions. For a turbocharger working under internal combustion engine conditions, the flow into the turbine is pulsatile and there are also unsteady secondary flow components, depending on the geometry of the exhaust manifold situated upstream of the turbine. Therefore, the effects of different perturbations at the inflow conditions on the turbine performance have been assessed. For the different cases both turbulent fluctuations and different secondary flow structures are added to the inlet velocity. The results show that a non-disturbed inlet flow gives the best performance, while an inflow condition with a certain large scale eddy in combination with turbulence has the largest negative effect on the shaft power output. / QC 20101111

A presente dissertação tem como objetivo principal estudar a propagação acústica em escoamentos monofásicos. Para tal, são analisados sinais transientes de pressão fornecidos por sensores instalados em posições conhecidas na linha de teste, através do estudo de técnicas de análise de sinais, a fim de investigar se as variações do conteúdo espectral dos sinais são influenciadas pela ocorrência de vazamentos no duto. A análise dos sinais foi realizada nos planos temporal, frequencial, tempo-frequência e estatístico. Os resultados experimentais foram obtidos no oleoduto piloto do NETeF - Núcleo de Engenharia Térmica e Fluidos da USP - Universidade de São Paulo, com uma seção de testes com 1500 metros e diâmetro de 51,2 mm, com escoamento monofásico de água. Os resultados obtidos através da análise tempo-frequência mostraram-se satisfatórios, sendo esta técnica capaz de identificar a composição espectral instantânea de um sinal, ou seja, foi eficiente na identificação de picos de amplitude da frequência ao longo do eixo temporal. Além disso, a análise probabilística, através do desvio-padrão do sinal também mostrou-se eficiente exibindo uma disparidade significativa entre os sinais com e sem vazamento. / The present dissertation reports on the study of the acoustic propagation in single-phase flow. It analyzes the transient signals provided by pressure sensors in known locations in the test line through the study of signal analysis techniques to investigate if the variations in spectral content of the signals are influenced by the occurrence of leaks in the pipe. The analysis of signals was performed in the time, frequency, time-frequency and statistical plans. The experimental results were obtained in a 1500 meter-long and 51.2 millimeter-diameter pilot pipeline at the Center of Thermal Engineering and Fluids, with single-phase flow of water. The results obtained by time-frequency analysis were satisfactory, allowing identifying the spectral composition of an instantaneous signal, i.e., the analysis was effective in identifying the frequency amplitude peaks along the time axis. Moreover, probabilistic analysis using the standard deviation of the signal was also efficient, displaying a significant disparity between the signals with and without leakage.

Scalar (heat or mass) transfer plays an important role in many industrial and engineering applications. Difficulties in experimental measurements means that there is limited detailed information available, especially in the near-wall region. Prediction in simple flows is well documented and the basis for development of many Computational Fluid Dynamics (CFD) models. This is, however, not the case for scalar transfer, especially when the Prandtl (Pr) or Schmidt number (Sc) is much greater than unity. In complex flows that involve separation and reattachment, the scalar transfer coefficient is significantly different to that of fully developed turbulent flow. The purpose of this Thesis is to investigate high Prandtl number (Pr ≥ 10) scalar transfer in fully developed (pipe) and disturbed (sudden pipe expansion) turbulent flow using CFD. Direct Numerical Simulation (DNS) is the most straight-forward approach to the solution of turbulent flows with scalar transfer. However, this technique is computationally intensive because all turbulent scales need to be resolved by the simulation. Large eddy simulation (LES) is a compromise compared to DNS. Instead of resolving all spatial scales, LES resolves only the large-scales with the small-scales being accounted for by a subgrid-scale model. Chapter 2 details the mathematical, numerical and computational details of LES with scalar transfer. From this, an optimized and highly scalable parallel LES solver was developed based on state-of-the-art LES subgrid-scale models and numerical techniques. Chapter 3 provides a verification of the LES solver for fully developed turbulent pipe flow. Reynolds numbers between Re = 180 and 1050 were simulated with a single Prandtl number of Pr = 0.71. Detailed turbulent statistics are provided for Re = 180, 395 and 590 with varying grid resolution for each Reynolds number. The results from these simulations were compared to established experimental and numerical databases of fully developed turbulent pipe and channel flows. The LES solver was shown to be in good agreement with the prior work with most discrepancies being accounted for by only reporting the resolved (large-scale) component directly reported from the LES results. For a Prandtl number close to unity, the mechanisms of turbulent transport and scalar transfer are similar. The near-wall region was shown to be dominated by large-scale sweeping structures that bring high momentum and scalar concentrations to the near-wall region. These are convected parallel to the wall as diffusion mechanisms act to transfer this to the wall where dissipation takes effect. An ejection structure then acts to transport the resultant low momentum, scalar depleted fluid back to the bulk to be replenished and continue the cycle. As the Prandtl number increases, molecular diffusivity decreases relative to viscosity, and the mechanisms of scalar transfer differ to those at Pr = 0.71. This is investigated in Chapter 4 using simulations at Re = 180, 395 and 590, with detailed statistics at Re = 395 for Pr = 0.71, 5, 10, 100 and 200. Where possible the results are compared to other numerical work and the LES solver was shown to accurately resolve the higher Prandtl number flows. There are marked variations in the scalar transfer with increasing Prandtl number as the turbulent scalar transfer becomes concentrated closer to the wall and dominated by large-scale turbulent structures. Sweeping structures are still responsible for bringing the high scalar concentrations towards the wall, however, high Prandtl number scalars are unable to completely diffuse to the wall in the time that the structure is convected parallel to the wall adjacent to the diffusive sublayer. Therefore, most of the high Prandtl number scalar is returned to the bulk via the ejection structure rather than being dissipated at the wall. Chapter 5 uses the sudden pipe expansion (SPE) to investigate disturbed turbulent flow for an inlet Reynolds numbers of Reb = 15600 and a diameter ratio of E = 1.6. These simulation parameters were chosen to match the experimental LDA measurements of Stieglmeier et al. (1989). The LES results for a range of grid resolutions were shown to be in very good agreement with the experimental work. From the LES results it was determined that the fluctuations in the wall shear stress are important in the near-wall turbulent transport. These are the result of eddies originating from the free shear layer down-washing and impinging upon the wall. This is a more effective sweeping mechanism than that observed for the fully developed turbulent pipe flow. Despite the down-wash structures impinging upon the wall, a viscous sublayer still exists in the reattachment region, albeit much thinner than the fully developed turbulent pipe flow further downstream. Using the same Reynolds number and diameter ratio, scalar transfer simulations were also undertaken in the SPE with Prandtl numbers of Pr = 0.71, 5, 10, 100 and 200. An applied scalar flux was used to heat the expanded pipe wall. The LES results are in agreement with experimental Nusselt numbers from Baughn et al. (1984) for Pr = 0.71. The disturbed turbulent flow enhances the scalar transfer and this is the result of down wash events transporting low (cold) scalar from the inlet pipe to the near-wall of the expanded pipe. This cools the heated wall and enhances localized scalar transfer downstream of the expansion. A diffusive sublayer still exists in the reattachment region within the viscous sublayer for Prandtl numbers greater than unity. As the Prandtl number increases the diffusivity decreases relative to viscosity and near-wall scalar transfer enhancement decreases as the diffusion time-scales increase.

Modern construction practices require proper knowledge to predict concrete pumping pressure, especially in high-volume and high-rise applications. Despite the progress made over the last decades, the spread of concrete pumping to high-rise construction has been hampered by the lack of standardized operating procedures and performance criteria. By and large, the guidelines available today focus predominantly on pumping Conventional Vibrated Concrete (CVC), while ambiguity still surrounds pumping Self-Consolidating Concrete (SCC) and other types of Highly-Workable Concrete (HWC). This PhD dissertation focuses on the fundamental principles relevant to the flow of high-strength SCC in pumping pipes, and it aims to develop methods to predict and reduce the required pumping pressure. The flow pattern of SCC in pipes is analytically investigated, providing a numerical approach to predict the pumping pressure based on the properties of both concrete and the lubrication layer, the pipe diameter, and the flow rate. The analytical results are further validated through full-scale pumping tests executed at the laboratory of the Université de Sherbrooke. Through this phase 26 optimal concrete mixtures were pumped in a 30-m pumping circuit to investigate the interactions between the concrete properties and pressure loss. The same tests are also employed to empirically correlate pressure loss with rheological and tribological properties of concrete at different flow rates. The resulting correlations furnish instrumental models capable of computing pressure loss for a wide range of concrete properties. In another application, the experimental results are analyzed to identify the influence of pumping on concrete properties with time. Full-scale pumping results are statistically analyzed in order to establish a quantitative description of the most influential parameters governing the concrete flow in pipes. As a result, concrete pipe flow is statically modeled, allowing the computation of pressure loss at different flow rates based on the the rheological and tribological properties of the concrete and the pipe diameter. Another statistical model is derived to calculate the pressure loss as a function of the V-funnel flow time, granting the advantage of predicting the pressure loss on job sites without the need for complex rheological and tribological measurements. In light of the research findings of the previous phases, a new simple test method called the pipe flow test (PFT) is developed in the context of this research, specifically for predicting pipe flow pressure loss. With preceding research phases as insights, the final stage of this project is directed toward mix design optimization faced with the challenge of reducing the pumping pressure and meeting the strength requirements of high-strength SCC. Ultimately, the research findings emanating from this investigation provide practical guidelines and conclusive models to predict and reduce pumping pressure for a wide scope of concrete mixtures and pipe diameters.