Machinery - Repository of the Faculty of Mechanical Engineering, University of Belgrade
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Theoretical and experimental investigation of the turbulent swirling flow characteristrics in circular pipes.
No full textThe investigation of turbulent swirling flow has a great theoretical and practical importance because their appearance in nature and technics is very habitual. However, these investigations are very complicated on account of the very complex structure of such a flow. Generally, these flows aren't investigated and a convenient turbulent model for their prediction has yet to be found. The basic aims of this investigation are the t- epsilon -turbulent model which is used for the calculation of such a flow and some local turbulent kinetic energy observations in the point of the vortex core radius. The investigations are based on our experiments and the experiments of other authors and the results for only one representative measuring series are shown, so the deduced conclusions for others are identical with the presented one. 2 Refs
Investigation on the incompressible turbulent swirling flow characteristics change along straight circular pipes.
No full textThe swirling flow field in any pipe cross section viewed from a cylindrical coordinate system a is characterized by the circumference velocity field, the axial velocity field, the radial velocity field, and the stream pressure field. Downstream, along the pipe, these profiles change under the 'control' of turbulent stresses thus producing the swirling flow characteristics change. The main aim of this paper is to show some possibilities of analytical prediction of changes of characteristic quantities, such as: circulation, averaged circulation, pipe wall stress and others. An analytical treatment of swirling flow is based on Reynolds equations for the case of stationary incompressible turbulent flow with body forces neglected
Modeling the Elastic Behaviour of Rubber in the Domain of Small Strain by Using Finite Element Method
No full textThe elastic behaviour of a rubbery material in the small strain domain has been analysed. Rubber is an incompressible material, which causes difficulties in modeling of its elastic behaviour. The finite element method is applied and the technique of reduced numerical integration is employed. The parabolic quadrilateral isoparametric finite element with 16 degrees of freedom is used. Three problems are solved and results are compared with the experimental data. The results obtained with the finite element method and reduced numerical integration are in excellent agreement with the experimental data in the small strain domain
Experimental investigation of notch sensitivity of thermomechanically treated aluminium alloy.
No full textA thermomechanically treated aluminum alloy containing 4. 5% Cu, 0. 6% Mn, 0. 6% Mg and 0. 4% Si has been experimentally investigated with regard to its notch sensitivity. The thermomechanical treatment consisted of quenching and ageing with different periods of precipitation, and different degrees of a cold plastic deformation afterwards. Five series of smooth and notched specimens were tested on a standard tensile machine and fracture surfaces were studied by TEM replicas. The Notch-Yield Ratio (NYR) and the fracture appearance were used as a measure of the notch sensitivity. It was found that certain thermomechanical treatments cause notch sensitivity and brittle fracture of notched specimens, even in the case of the low value of sigma //0//,//2/// RHO ratio. Thermomechanical treatment consisting of 120 minutes precipitation and 30% or 40% deformation degree of cold rolling deformation can be recommended as the most suitable for structural application
The energetic characteristic scale-up calculation of the smaller to the bigger tube model turbine with the evident distinction of the hydraulic design of inlet water passages.
No full textFor the hydroelectric power station 'DJERDAP II' with tube turbines the energetic characteristics on the model turbine test identical to the full size (runner diameter D SUB 1 = 0.460 m) are performed. The complete characteristics, up to nondimensional unit speed n SUB 1 SUB 1/n SUB 1 SUB 1 SUB gL = 1.65 are determined, because the features of the test bed were limited. But, for the nondimensional unit speeds in the range 1.65 n SUB 1 SUB 1/n SUB 1 SUB 1 SUB gL 2.83 which is of the great interest for the full size turbine operation, the energetic characteristics on the mentioned test bed cannot be obtained. For this purpose, the second cavitation test bed with the smaller model turbine (runner diameter D SUB 1 = 0.250 m) is used. The obtained results could not be used directly because there was the evident distinction between the hydraulic design of the inlet water passages of the first model test bed and the full size plant. Even the turbine shaft bearings were quite different. Finally, for the scale up calculation the well known formulae (Hutton, Ackeret, Etinberg, Osterwalder, ...) for so wide range of turbine operation could not be used for such a wide range of turbine operation because the outside operation point of the optimum efficiency (points of the less efficiency) they give the unreal corrective valves. (from authors' abstract
