Aaltodoc Repository :: Browsing by Author "Siikonen, Timo"

Browsing by Author "Siikonen, Timo"

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The aerodynamic design of range limited and long range projectiles
(2010) Karstunen, Juha; Sailaranta, Timo; Sovelletun mekaniikan laitos; Insinööritieteiden korkeakoulu; School of Engineering; Siikonen, Timo
The purpose of this thesis is to give an overview to the aerodynamics of small arms' projectiles. The thesis also acts as a preliminary study for upcoming research related to range limited and long range projectiles' development in the Flight mechanics research group at the Aalto University Department of Applied Mechanics. There are several aerodynamic forces and moments at transonic and supersonic speed ranges affecting the projectile and causing inaccuracy. A shape of the projectile and, for example the location of the centre of gravity, has a great effect on these forces and moments. Particularly, the transonic flow around the projectile, having asymmetric and time independent characteristics, is a challenging field of research. Range limited projectiles, mainly designed for training purposes, and are characterized by having good accuracy on a certain range but also having an ability to efficiently decrease the speed after reaching the desired range. According to previous studies, one effective way to restrict the projectile's range is to increase the drag by contributing the projectile to achieve a gyroscopically unstable flight mode. During the unstable flight, the angle of attack increases causing the drag to increase. For instance, small streamwise fins or grooves located in the projectile's boattail increase the spin damping moment and enhance the formation of an unstable flight mode. For the long range projectile, it is important to maintain a stable flight over a 1.5 km range. Decreasing the drag, for example by redesigning nose and boattail shapes, contributes the projectile to maintain the supersonic flight longer. Improving projectile's transonic flight characteristics and weakening the disturbances caused by variation of angle of attack and Magnus-effect are challenging fields of research in the future. A computational study has been undertaken for the Lapua .338 Magnum Scenar long range projectile to determine its aerodynamic characteristics. The CFD-simulation was conducted by using Ansys Fluent -software for six different Mach numbers and two angles of attack. Results and gathered experience from this thesis will be used in upcoming research on improving the performance of long range and range limited projectiles.
Aerodynamic noise in the supersonic nozzle flow
(1993) Pitkänen, Harri; Siikonen, Timo; Simula, Markku; Konetekniikan osasto; Teknillinen korkeakoulu; Helsinki University of Technology; Laine, Seppo
Analysis of a gas flow in structured packed bed columns using computational fluid dynamics
(2013) Jäntti, Niina; Vaittinen, Johanna; Sovelletun mekaniikan laitos; Insinööritieteiden korkeakoulu; School of Engineering; Siikonen, Timo
In many countries, fossil fuels are a vast energy resource in spite of sector of renewable energy resources. Large amounts of carbon dioxide are produced by the power plants using fossil fuels, like coal, peat and natural gas. The CO2 emissions induce global warming which leads to the fact that releasing CO2 into the atmosphere is no longer environmentally sustainable. A common technology for carbon dioxide recovery is the post-combustion carbon dioxide capture via absorption. The post-combustion carbon-dioxide capture is conducted typically in structured packed bed columns which have large dimensions, since the flue gas streams to the absorber are vast. Controlling the flow is difficult due to the large dimensions and maldistribution is a real problem. Maldistribution of the flue gas and the liquid solvent in the absorber bed decrease mass transfer efficiency in the column. In this work, flow field and gas phase distribution in a structured packed bed column is studied by means of computational fluid dynamics (CFD). A porous medium model for a structured packed bed is created with aid of experimental results from literature. The porous medium model is validated against pressure loss measurements and maldistribution measurements. According to the comparison between simulations carried out and experimental results from literature, the anisotropic porous model seems to capture the gas phase maldistribution quite well. Finally, the model is applied for an industrial scale column, and it is noticed that it is not guaranteed that a severe maldistribution will smooth out even in a relatively high bed. Flow in a packed bed is complicated, thus simplifications were made in this study. In order to increase the model reliability, some propositions for improving the model are given in the end of this work.
Analysis of aerodynamic stability of the MetNet entry and descent vehicle with FINFLO simulations
(2015-11-23) Palin, Matti; Siikonen, Timo; Harri, Ari-Matti; Insinööritieteiden korkeakoulu; Tuhkuri, Jukka
This Master's Thesis investigates the aerodynamic stability of the MetNet Mars atmospheric entry and descent vehicle, developed in cooperation between the Finnish Meteorological Institute (FMI) and the Lavochin Association (LA). The purpose of the study is performing Computational Fluid Dynamics (CFD) simulations and obtaining the pertinent aerodynamic coefficients for the vehicle in the landing phase to Mars. The results are compared with the values obtained by LA, the most important feature being the aerodynamic stability of the vehicle. In this work, only the static stability is assessed. The simulations were performed with an inhouse FINFLO software. Before the simulations, an atmospheric model of Mars was created. Some initial trajectory calculations were made in order to have approximate values for the combinations of the Reynolds and Mach numbers that the vehicle will experience during the landing. These initial trajectory calculations also provided a condition for the mesh creation. A coarse and a dense calculation meshes were created with 1.4 and 7 million cells, respectively. The SST k-ω turbulence model was used and the results were tabulated in a form of dimensionless coeffcients. Apart from the lift coeffcient, the values differ to some extent from the LA's results. However, the general trends lead to the same conclusions: the drag coeffcient is more than suffcient to ensure the designed landing speed and the negative slope of the pitching moment coeffcient indicates static stability for the vehicle. Some heat load analyses were also carried out. Unfortunately, the simulations converged only up to Ma = 1,9 and no results were obtained at larger velocities. The thermal analyses show that heating of the vehicle is highly dependent on the Mach number, and for these reasons it would be advisable to perform more simulations for the vehicle.
Analysis of multi-propeller marine applications by means of computational fluid dynamics
(2014-05-19) Turunen, Tuomas; Rauti, Timo; Insinööritieteiden korkeakoulu; Siikonen, Timo
Työssä tarkastellaan laskentamenetelmiä, joiden avulla voidaan analysoida useampipotkurisia meritekniikan laitteita. Tavoitteena on luoda laskentatyökalu, jolla voidaan parantaa olemassa olevia laitteita ja arvioida uusien konseptien suorituskykyä ja siten suunnitella hyötysuhteeltaan nykyistä parempia tuotteita. Ensiksi käydään läpi tällä hetkellä saatavilla olevia laskentamenetelmiä ja arvioidaan niiden soveltuvuutta kirjallisuustutkimuksen avulla. Potkurin pyöriminen mallinnetaan MRF-menetelmällä sekä pyörivän hilan menetelmällä, jossa hilan eri osat on erotettu niin sanotulla liukuvalla pinnalla. Turbulenssi mallinnetaan RANS-tyyppisellä kaksiyhtälömallilla SST k-omega. Teoria, johon laskentamenetelmät perustuvat, käydään läpi ja mallien toimivuutta tutkitaan vertaamalla laskettuja tuloksia mittauksiin. Vertailutapauksia on kaksi. Ensimmäisessä tapauksessa on yksi potkuri avovesiolosuhteissa ja toisessa tapauksessa yksikkö, johon kuuluu vastakkain pyörivä potkuri (CRP). Laskenta tehdään avoimen lähdekoodin virtaussimulointiohjelmistolla OpenFOAM-2.2.x, jossa sovelletaan esitettyjä laskentamenetelmiä. Kaikki käytetyt menetelmät toimivat yksittäin, mutta edelleen tarvitaan jatkotutkimuksia, jotta saavutettaisiin tavoiteltu laskentatyökalu useampipotkuristen laitteiden analysoimiseen.
Analysis of the flow around a cruise ferry hull by the means of computational fluid dynamics
(2014-11-24) Asén, Patrik; Mikkola, Tommi; Insinööritieteiden korkeakoulu; Siikonen, Timo
In this thesis computational fluid dynamics (CFD) is used to determine the drag of a cruise ferry in a double hull, as well as a free-surface case. The computations are done with OpenFOAM-software. Both cases are computed with five different grid spacings. The results obtained are compared to findings from towing tank experiments, as well as to each other in order to distinguish between the differences of the two cases. The computations in OpenFOAM are based on the finite volume method. Turbulence is modelled with the STT k-$\omega$ method by Menter. The free surface is treated with the Volume of Fluid (VOF) method. The computations are done on a set of geometrically similar grids with the number of cells between $0.14-0.44$ million for the double hull cases, and between $0.6 -2.2$ million for the free-surface cases. All the cases are run with the same Reynolds number of $20$ million. The ship hull is considered to advance at a constant velocity in deep and calm water. The flow is considered incompressible. The results are presented in a non-dimensional form. The drag is presented as the drag coefficient and it is compared to experimental towing tank results. The shear stress distributions as well as the pressure distributions for the double hull case are compared to those from the free-surface case. The results obtained for the total drag are satisfactory when compared to earlier findings. The results were also accurate enough to distinguish clear differences between the double hull and free-surface cases. However, the grid refinement was not completely successful, as the solution did not converge on the finer grids. The reason behind this is not completely understood.
Application for inverse simulation of flight tracks
(2012) Leinonen, Antti Kalevi; Sailaranta, Timo; Sovelletun mekaniikan laitos; Insinööritieteiden korkeakoulu; School of Engineering; Siikonen, Timo
An application for inverse simulation of flight tracks is implemented. Such an application is required for analysis of flight accidents and verification of flight tracks that are generated using optimization methods. The application could also be used to support monitoring of aircraft fatigue life through the flight parameters. The application is required to utilize a simplified aerodynamic model to analyse flight tracks that are given in the form of the aircraft position at successive time steps. Such data from actual flights could be recorded using a GPS device or radar. The most recognized inverse simulation methods are reviewed. The method selected for this work is based on successive numerical differentiation of the flight track to obtain velocity and acceleration vectors. To obtain a solution for the flight attitude, coordinated flight is assumed, i.e. the aircraft has no sideslip or side force. The contribution of the thrust to the lift is considered, and a technique is formulated to recognize the sections of the flight track flown using a negative load factor. Also the wind conditions are considered. The application is implemented in the Matlabr environment. The inverse simulation is verified using data from flight simulations. It is shown that the results of the inverse simulation are accurate if the initial data are accurate and the assumption of coordinated flight is valid. The flight parameters that are computed via the inverse simulation include speed, Mach number, thrust setting, angle of attack, Euler angles, angular rates and load factor vector. Data from actual flights may require processing, i.e. smoothing and filling, before good results can be obtained.
Application of pressure- and density-based methods for different flow speeds
(John Wiley and Sons Ltd, 2015) Miettinen, Ari; Siikonen, Timo; Department of Applied Mechanics
Automatic zoning for combined CFD and multiblock modelling
(2008) Seppälä, Maiju; Manninen, Mikko; Sovelletun mekaniikan laitos; Teknillinen korkeakoulu; Helsinki University of Technology; Siikonen, Timo; Ahlstedt, Hannu
Azipod flow analysis in oblique flow conditions with potential flow methods
(2016-05-16) Tuulio, Mikko; Siikonen, Timo; Korsström, Andrei; Insinööritieteiden korkeakoulu; Tuhkuri, Jukka
The subject of this master thesis is hydrodynamic forces effecting on an azimuthing thruster in oblique inflow. To calculate the forces two methods are developed. The first one is based on statistical data, propeller open water coefficients and a dynamic pressure. The second one uses a propeller blade element method, which is corrected with a propeller momentum theory in respect to generated thrust. The blade element method uses a panel method, which takes a flow separation into account. It was discovered, that it is possible to model hydrodynamic forces on the azimuthing thruster in an oblique flow with simple coefficients. The Blade element momentum method provided results, that compare poorly to the experimental data.
Cavitation on Model- and Full-Scale Marine Propellers : Steady And Transient Viscous Flow Simulations At Different Reynolds Numbers
(MDPI AG, 2020-02-01) Viitanen, Ville; Siikonen, Timo; Sanchez-Caja, Antonio; VTT Technical Research Centre of Finland; Department of Mechanical Engineering
In this paper, we conducted numerical simulations to investigate single and two-phase flows around marine propellers in open-water conditions at different Reynolds number regimes. The simulations were carried out using a homogeneous compressible two-phase flow model with RANS and hybrid RANS/LES turbulence modeling approaches. Transition was accounted for in the model-scale simulations by employing an LCTM transition model. In model scale, also an anisotropic RANS model was utilized. We investigated two types of marine propellers: a conventional and a tip-loaded one. We compared the results of the simulations to experimental results in terms of global propeller performance and cavitation observations. The propeller cavitation, near-blade flow phenomena, and propeller wake flow characteristics were investigated in model- and full-scale conditions. A grid and time step sensitivity studies were carried out with respect to the propeller performance and cavitation characteristics. The model-scale propeller performance and the cavitation patterns were captured well with the numerical simulations, with little difference between the utilized turbulence models. The global propeller performance and the cavitation patterns were similar between the model- and full-scale simulations. A tendency of increased cavitation extent was observed as the Reynolds number increases. At the same time, greater dissipation of the cavitating tip vortex was noted in the full-scale conditions.
CFD predictions of unsteady cavitation for a marine propeller in oblique inflow
(Elsevier Ltd, 2022-12-15) Viitanen, Ville; Sipilä, Tuomas; Sánchez-Caja, Antonio; Siikonen, Timo; Department of Mechanical Engineering; Marine Technology; VTT Technical Research Centre of Finland; ABB Group
In this paper the Potsdam Propeller Test Case is numerically investigated in oblique inflow conditions. We consider three different topics: open water performance curves, cavitation observations, and pressure pulses induced by the propeller to the ceiling of the cavitation tunnel. In the oblique flow case, the inflow is not uniform from the perspective of the propeller, which results in the dependency of the propeller blade loading and cavitation on the blade rate frequency. The numerical simulations were compared to experimental results for each investigated case. Additionally, we analyzed the unsteady features of the cavitation on the blades as well as the pressure peaks in the propeller wake due to collapsing cavities. We found that the global performance and cavitation patterns close to the blades agree well with the tests in the numerical simulations. The agreement with the tests for the pressure pulses on the tunnel ceiling was better in the non-cavitating case. The unsteady cavitation shed behind the propeller and the subsequent collapse events induced a vast increase in recorded maximum pressure values. Root cavitation collapse produced pressure pulses an order of magnitude greater than the collapse of tip vortex cavitation. Also the collapse of cavities on the blades contributed to a significant increase in the pressure fluctuations on the blades.
Compressible two-phase viscous flow investigations of cavitation dynamics for the ittc standard cavitator
(Springer International Publishing AG, 2020-10-07) Viitanen, Ville M.; Sipilä, Tuomas; Sánchez-Caja, Antonio; Siikonen, Timo; VTT Technical Research Centre of Finland; ABB Group; Department of Mechanical Engineering
In this paper, the ITTC Standard Cavitator is numerically investigated in a cavitation tunnel. Simulations at different cavitation numbers are compared against experiments conducted in the cavitation tunnel of SVA Potsdam. The focus is placed on the numerical prediction of sheet-cavitation dynamics and the analysis of transient phenomena. A compressible two-phase flow model is used for the flow solution, and two turbulence closures are employed: a two-equation unsteady RANS model, and a hybrid RANS/LES model. A homogeneous mixture model is used for the two phases. Detailed analysis of the cavitation shedding mechanism confirms that the dynamics of the sheet cavitation are dictated by the re-entrant jet. The break-off cycle is relatively periodic in both investigated cases with approximately constant shedding frequency. The CFD predicted sheet-cavitation shedding frequencies can be observed also in the acoustic measurements. The Strouhal numbers lie within the usual ranges reported in the literature for sheet-cavitation shedding. We furthermore demonstrate that the vortical flow structures can in certain cases develop striking cavitating toroidal vortices, as well as pressure wave fronts associated with a cavity cloud collapse event. To our knowledge, our numerical analyses are the first reported for the ITTC standard cavitator.
Control Volumes in Computational Fluid Dynamics
(2010) Yondo Mine, Guy Raoul; Insinööritieteiden ja arkkitehtuurin tiedekunta; Siikonen, Timo
DDES of wetted and cavitating marine propeller for CHA underwater noise assessment
(2018-05-21) Viitanen, Ville M.; Hynninen, Antti; Sipilä, Tuomas; Siikonen, Timo; Department of Mechanical Engineering; Marine Technology; VTT Technical Research Centre of Finland
In this paper we present results of delayed detached eddy simulation (DDES) and computational hydroacoustics (CHA) simulations of a marine propeller operating in a cavitation tunnel. DDES is carried out in both wetted and cavitating conditions, and we perform the investigation at several propeller loadings. CHA analyses are done for one propeller loading both in wetted and cavitating conditions. The simulations are validated against experiments conducted in the cavitation tunnel. Propeller global forces, local flow phenomena, as well as cavitation patterns are compared to the cavitation tunnel tests. Hydroacoustic sources due to the propeller are evaluated from the flow solution, and corresponding acoustic simulations utilizing an acoustic analogy are made. The propeller wake flow structures are investigated for the wetted and cavitating operating conditions, and the acoustic excitation and output of the same cases are discussed.
De Havilland Comet
(2009) Heikkilä, Panu; Siikonen, Timo; Insinööritieteiden ja arkkitehtuurin tiedekunta; Marquis, Gary
Design of a wind tunnel model of a supersonic missile inlet
(2012) Acosta, Daniel Mikael; Pankkonen, Antti; Sovelletun mekaniikan laitos; Insinööritieteiden korkeakoulu; School of Engineering; Siikonen, Timo
In this work, the design of a supersonic inlet wind tunnel model is defined and evaluated. The small-scale model enables experimental investigation of the on-and off-design operation of an external compression inlet, typically used by air-breathing air-to-air missiles. A generic inlet geometry featuring a design Mach number of 3, combined with the size of the wind tunnel test section area served as the starting point for this project. The undertaken task consists of constructional design, strength analysis and aerodynamic evaluation. The model design includes a mechanism that enables the control of pressure at the back of the inlet. The combination of a wedge and an adjustable box allow the regulation of the inlet exit area, taking into account the desired steadiness of the airflow. Consequently, all operational modes are achievable during a single wind tunnel run. Model support is provided by the vertical strut of the trisonic wind tunnel of the Aerodynamics Research Group of the Aalto University, thus allowing the adjustment of the angle of attack. A measurement arrangement is designed in order to obtain the static pressure distribution throughout the centre line of the model and an accurate value for the total pressure recovery, a parameter defining the efficiency of an inlet. Additionally, the model is equipped with two windows located on the side walls of the inlet, thus enabling the use of Schlieren flow visualization at the cowl lip and the external compression field. Suitable wind tunnel test section windows are also designed and acquired. Furthermore, oil flow visualization will also be used in order to analyse the internal duct flow. The experimental data obtained by this test arrangement will provide insight into flow phenomena in a supersonic inlet, which will be used for the verification and validation o of numerical simulations.
Design of airplane wing anti-icing fluid tests in wind tunnel
(2013) Rinne, Antti Alpo; Kivekäs, Juha; Sovelletun mekaniikan laitos; Insinööritieteiden korkeakoulu; School of Engineering; Siikonen, Timo
Three wind tunnel test set-ups for the research of the effects of de-and anti-icing fluids on transport airplane take-off performance at arctic conditions are designed. Implementation of the set-ups and performing the tests in the Aalto University subsonic wind tunnel are described. Processing of the results is instructed and a method is developed for determining the average thickness of a fluid layer on a wind tunnel model surface from pictures of the layer. In the first test set-up an existing wind tunnel model is utilised to study the fluid flow-off mechanism. A video is shot of the test and the average fluid thickness is determined from the screen captures. For the second set-up a flat plate elimination test (FPET) duct is designed on the basis of SAE Aerospace Standard AS5900. The dimensions are enlarged to ensure operation in a wind tunnel with a larger test section than for which the standard was developed. In this test the boundary layer displacement thickness on the duct floor is measured. In the third set-up a wing profile model representative of a modern transport airplane wing and equipped with adjustable lift-enhancing devices is used. Take-off run and rotation of a transport airplane are simulated and the lift coefficient is measured in this test. Test runs with the set-ups are performed and the results are processed. The results obtained with the fluid thickness determination method are observed to be reasonable. Also the flat plate elimination test results are observed to be comparable to the published results from AS5900 compliant tests.
Determining wind loads for large vertical lift fabric doors
(2017-06-12) Rajamäki, Mika; Siikonen, Timo; Insinööritieteiden korkeakoulu; Tuhkuri, Jukka
The purpose of this thesis was to research how wind loads are determined for large vertical lift fabric doors. The work focuses mainly on the European standard and its use, even though other standards are mentioned. For this thesis an Excel-program was made for a purpose of calculating wind loads using the European norm 1991-1-4. Process for calculating the wind loads and the theory behind it are in this written part of the thesis. In the beginning of this thesis the theory of the wind is described and what a wind means as physical and meteorological phenomena. After this a method how to deﬁne the wind load analytically is presented. Then the available standards are described. First how the wind load calculation is handled in the European standard 1991-1-4 and after that we quickly go through the same process in the American standard ASCE 7-10. Next the Excel-program that was created for the purpose of calculating wind loads is described. Last it is time to sum up on what was made in this thesis and how the work could be further improved. Using a diﬀerent standard gives acceptable results when compared to experimental methods. However, results can vary noticeably between diﬀerent standards. This means that designing large vertical lift fabric doors is not optimised if different standards are used. It could be possible that using computational ﬂuid dynamics the optimisation could be better but this is a subject for a next research topic.
Development of an aero-acoustic postprocessing programme
(2002) Heikkilä, Ulla; Dickmann, Hans-Peter; Konetekniikan osasto; Teknillinen korkeakoulu; Helsinki University of Technology; Siikonen, Timo

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