Browsing by Author "Majander, Petri"

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  • A comparison of complete vs. simplifed viscous terms in boundary layer flow and lid-driven cavity flow
    (1997) Majander, Petri
     Helsinki University of Technology | J Muu elektroninen julkaisu
    Abstract: Viscous terms are derived in curved co-ordinates using finite volume formulation. An approximation in common use called Thin Shear Layer approximation is derived. Turbulent flow over a flat plate with a k- ε-model as well as a laminar lid-driven flow are computed and the results are compared between the full viscous terms and the TSL approximation. Main result: An implementation of full viscous terms in FINFLO solver.
  • A computation of a flow over a cylinder with a three-dimensional pressure correction solver
    (1998) Majander, Petri
     Helsinki University of Technology | J Muu elektroninen julkaisu
    Abstract: A three dimensional flow solver is tested with external flow over a cylinder. The Reynolds number of the flow is 40. The convergence of the problem is studied with multigrid and line-Gauss-Seidel solvers for the pressure correction equation. Different ways to implement periodic boundary conditions are compared. Main result: A presentation of a three-dimensional pressure correction solver. The convergence slows down by a factor of three, if the periodic boundary conditions are ignored in the implicit phases.
  • Design and implementation of an indirect refrigeration system for laboratory testing
    (2019-12-16) Koivisto, Jaakko
     Insinööritieteiden korkeakoulu | Master's thesis
    New products and concepts are being constantly developed in worldwide refrigeration business. Modern challenges and opportunities drive some development towards more environmentally friendly and smart refrigeration, with smaller demands for space and installation expenses. Indirect refrigeration systems have their own advantages, such as possibility of very small refrigerant charges compared to direct systems, especially with long piping and many cooling targets. Viessmann ESyCool is an advanced and comprehensive energy system for food retail stores. ESyCool system utilizes indirect refrigeration. Aim of this work is to design and implement an indirect refrigeration system for laboratory testing of various indirect refrigeration products and equipment, including some from ESyCool. Some relevant refrigeration technology and theory are also introduced, including a proper review of vapor compression, CO2 and indirect refrigeration systems. All in all, this project was successful and a working system with wanted properties was accomplished. Decades of high quality indirect refrigeration can be achieved with the project’s refrigeration plant if recommended adjustments, operation and maintenance are carried out. Based on this study, for around 10-50kW similar kind of indirect refrigeration plant projects, considerably good results can be achieved with design according to appendixes 4-7 and 10, and details described in this work. For implementation, significantly shorter installation times and a bit higher quality can be reached with means mentioned and discussed in this work. This project and its learnings can be used as a benchmark for similar custom made energy production plant projects in future, especially in refrigeration branch.
  • Developments in Large Eddy Simulation
    (1999) Majander, Petri
     Helsinki University of Technology | Licentiate thesis
  • Large-eddy simulation of a round jet in a cross-flow
    (2006-12-01) Majander, Petri
     Doctoral dissertation (article-based)
    Several aspects of large-eddy simulations (LES) are studied in this thesis. In the first part computational requirements and methods are compared for the calculation of unsteady incompressible flow. Explicit time integration methods are efficient especially in simple flow geometries and with low Reynolds numbers. An Adams-Bashford fractional time-stepping scheme is used in the turbulent channel flow computations. The Smagorinsky model is a baseline subgrid-scale model used in LES. This and the dynamic version are assessed in a turbulent channel flow. The models do not necessarily improve the results at a low Reynolds number if the calculation is stabilized enough by the molecular or numerical viscous effects. With the second-order central scheme the numerical error is estimated to be greater than the filtered stresses from the momentum equations. This estimate alone suggests that there is no accurate model for instantaneous stresses for the low-order schemes. The main role of the subgrid-scale model is to remove energy from the resolved scales and hence to stabilize the calculation. LES in any practical application, even at a low-Reynolds number, requires high computational resources. A parallel solver based on a multi-block approach is written, where computational domain is divided between many structured blocks. The blocks assigned to different processors communicate at the boundaries with an MPI standard. The solver is tested with a turbulent cavity and a pipe flow. A linear speed-up and scale-up are achieved with equally balanced processors loads. A large-eddy simulation of a round jet penetrating normally into a cross-flow is computed. The jet-to-cross-flow velocity ratio is 2.3 at a Reynolds number of 46 700, based on the jet bulk velocity and the jet diameter. The simulation is performed both with a steady and an unsteady boundary condition at the jet inlet pipe. A passive scalar is discretized both with a central and a TVD discretization. The results are compared with each other and the experimental measurements of Crabb, Durão and Whitelaw. The computation reproduced many phenomena present in such a flow, like the shear layer ring vortices and a counter-rotating vortex pair. In general, a reasonable agreement with the measurements was obtained. The unsteady boundary condition at the jet inlet increases the spreading of the jet slightly.
  • Method of Large Eddy Simulation Applied to Recirculating Ventilation Flow in a Room
    (2008) Brockmann, Tomas
     Helsinki University of Technology | Master's thesis
    The purpose of this work was to become familiar with OpenFOAM and to apply the large eddy simulation method to some low-Reynolds-number flow case. OpenFOAM is a C++ library that is enjoying growing interest around the world. Its main purpose is to allow the creation of applications for the solution of fluid dynamic problems. The large eddy simulation method is a way of modelling turbulence. The effects of small eddies are modelled while the flow is solved accurately on the large scale. This work began with a channel flow simulation to get used to computational fluid dynamics. The essential work then was to solve an indoor ventilation flow case by applying the large eddy simulation method. Traditionally, turbulent flows are solved in such a way that turbulence is completely modelled and only a steady-state flow solution is solved. Such a result depends heavily on the properties of the turbulence model applied and the solution is not always realistic. The large eddy simulation method is considered as an increasingly interesting alternative since the required number-crunching resources are becoming affordable. Computational times appeared prohibitively long without parallel running on many, preferably dozens of cores. The required computational effort limits the size and complexity of the mode to be simulated. Simulation results do not quite match the corresponding experimental measurements, but most of this can be attributed to the lack of inflow turbulence. Apart from this,the results appear promising. Some time-averaged simulations were applied to the indoor ventilation case too, but the turbulence models appeared to have their shortcomings.
  • Mössbauer study of magnetostrictive Tb0.3Dy0.7Fe2-compound
    (1995) Majander, Petri
     Helsinki University of Technology | Master's thesis