This paper presents semi-analytical calculations, computational fluid dynamic simulations and experimental measurements accomplished on a typical 30MVA power transformer. An ad-hoc workbench was devised to carry out the experimental measurements. This facility allowed to estimate the values of different key variables involved in heat dissipation within the radiator, like convective heat transfer coefficients, oilflow rate, air-flow speed between radiator fins and overall dissipated heat, among others. The main objectives of the study are to analyze the cooling capacity of the current radiator design working in ONAN mode and to validate the numerical simulation and calculation procedures for further design optimizations. The coupled thermo-hydraulic numerical simulations were performed on a computer cluster due to the high computational cost of the resulting models. The results of the simulations show good agreement with the experimentally measured values and with those obtained with the semianalytical model, thus confirming that this model together with the CFD simulations are an accurate analysis tool. The heat transfer coefficients in the oil, the radiator panel and the air are computed. It is found that convective heat transfer from the panel to the air is approximately 10 times lower than heat transfer in the oil. Possible improvements on the current radiator design are briefly mentioned.

a b s t r a c tThe aim of this paper is to analyze the aeroelastic processes developed during the starting phase of a rocket engine via a coupling fluid/structure code. This analysis gives a better understanding of the behavior of the structure as the shock waves propagate inside the engine nozzle. The gasdynamics Euler equations are solved for the fluid and constitutive linear elastic solid assuming large displacements and rotations with no material damping is adopted for the structure. The coupling of each subproblem is carried out with a Gauß-Seidel algorithm over the fluid and structure states. For the fluid problem an ALE (Arbitrary Lagrangian-Eulerian) formulation is used. It allows us to define a reference system following the moving boundaries while the structure is deformed. The code is validated with a study of the flutter phenomena that may occur when a supersonic compressible fluid flows over a flat solid plate. Regarding the rocket engine ignition problem, a modal analysis of the structure is performed in order to analyze the eigenfrequency shifts when considering the coupling with the fluid flow.