Seminar Mechanics of Machines and Mechanisms - Models and Mathematical Methods

 

PROGRAM

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Plan rada Seminara Mehanika mašina i mehanizama - modeli i matematičke metode za APRIL 2023.

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UTORAK, 04.04.2023. u 17:00, sala 301f, Kneza Mihaila 36 i Live stream
Dejan Ilić, Faculty of Mechanical Engineering, University of Belgrade, Serbia
EXPERIMENTAL RESEARCH OF TURBULENT SWIRLING FLOW BEHIND THE AXIAL FANS IN DIFFUSERS
The turbulent swirl flow in three conical diffusers has been the subject of extensive experimental research. Diffusers have the same inlet diameter of 0.4 m and different total divergence angles: 8.6°, 10.5°, and 12.6°. The swirl flow field was generated by the axial fan impeller. Various swirl parameters were achieved by the impeller openings and rotational speeds, and additional regulating valve and booster fan were sometimes applied. The original classical probes were used in each of these diffusers, and laser Doppler anemometry (LDA) was used in one diffuser. Comparative measurements of axial and circumferential velocities are presented. All generated flows are extremely turbulent, and sometimes reverse flows occur in the central flow region. The time-averaged circumferential velocity profiles obtained with that impeller are solid body profiles. Volume flow rate, average circulation, swirl number, pressure recovery, and hydraulic efficiency are all determined as integral parameters. The distributions of the average main swirl flow characteristics along the diffuser are presented. Distributions of the inlet Boussinesq number, outlet Coriolis coefficient, and ratio of the swirl and pure axial flow loss coefficients at conical diffusers on the inlet swirl flow parameter are also shown. The statistical characteristics, such as turbulence levels, skewness, and flatness factors, were calculated and analyzed for one diffuser. This research belongs to research conducted within the School of the turbulent swirling flow at the Faculty of Mechanical Engineering, University of Belgrade.

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UTORAK, 25.04.2023. u 17:00, sala 301f, Kneza Mihaila 36 i Live stream
Nikola Marković, Mathematical Institute of the Serbian Academy of Sceinces and Arts, Belgrade, Serbia
DEVELOPMENT OF A METHOD FOR THE CALCULATION OF MULTISTAGE GAS TURBINES AND ESTIMATION OF THE REQUIRED AMOUNT OF COOLING AIR
The main task of designing a gas turbine process is to achieve maximum efficiency by expanding maximum efficiency coefficient within the limitations related to the stress level of the blades, dimensions of the machine, economic factors or other factors. The mentioned limitations, during design, lead to a creation of wide range models and structures (solutions) of Gas Turbines. However, in this paper the emphasis will be placed on pure aerodynamic calculation and achieving the maximum efficiency coefficient. In considering the aerodynamic calculation of single-stage turbines at the mean diameter, the greatest influence on the efficiency coefficient is due to the dimensionless parameters of the turbines. The axial velocity ratio and the inlet-to-outlet mean diameter ratio have a minor effect on the efficiency coefficient than the loading coefficient and the flow coefficient. For that reason, loading coefficient and flow coefficient are primarily considered in this paper, whereby the highest priority is given to the loading coefficient as the most influential parameter. The other two parameters can be ignored. It is not possible to define any exact mathematical relation that links the dimensionless and other parameters of the turbine with the efficiency coefficient that is achieved. Therefore, the developed mathematical model in this paper is based on the Fielding model, where the variation of dimensionless parameters, that have the greatest influence on efficiency coefficient, is achieved by variating the blade velocity of the first stage in the group and flow coefficient. The parameters that directly depend of it includes loading coefficient, degree of reaction, the ratio of the diameter at the root and the tip of the blade, as well as the minimum permissible ratio of the diameter of the root and the tip. The gas flow is considered as a semi-ideal gas, with attribute of changing thermophysical properties depending on temperature, given that, the pressure change has negligible effect on the properties of gas. In the other hand, if we took the pressure change into consideration our model and calculations will be extremely complex to solve in real time.
The solutions obtained in this work assume a one-dimensional calculation at the mean diameter based on the given input parameters. The developed mathematical model can be divided into two parts: 1 - Calculation of the equivalent (imaginary) gas turbine. Calculation of equivalent turbine consists of three steps: a) variation (optimization) of the loading and flow coefficients and important parameters of the GT, b) definition of physical implementation limits c) selection of optimal GTs dimensionless parameters at which the maximum value of the efficiency coefficient will be achieved. 2 - Calculation of the GT with blade cooling mechanism. Calculation consists of the following steps: a) definition of the cooling model, b) detailed thermodynamic calculation of the GT stage, c) determination of the required amount of cooling air.
The presented research is a part of the Master's thesis at the Faculty of Mechanical Engineering in Belgrade, under the mentorship of professor Milan Petrović. This research is the result of joint work with Professor Petrović, whom I would like to thank for his support, guidelines and suggestions.

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Seminar Mehanika mašina i mehanizama - modeli i matematičke metode započeo je sa radom u junu 2018.god. Seminar se održava do dva puta mesečno, utorkom u periodu od 17.00 - 19.00 u Matematičkom institutu SANU.

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