Computational Fluid Dynamics (CFD) results are often presented in a deterministic way despite the uncertainties related to boundary conditions, numerical modelling, and discretization error. Uncertainty quantification is the field studying how these phenomena affect the numerical result. With these methods, the results obtained are directly comparable with the experimental ones, for which the uncertainty related to the measurement is always shown. This work presents an uncertainty quantification approach applied to CFD: the test case consists of an industrial prismatic gas turbine vane with standard film cooling shaped holes system on the suction side only. The vane was subject of a previous experimental test campaign which had the objective to evaluate the film cooling effectiveness through pressure-sensitive paint technique. CFD analyses are conducted coherently with the experiments: the analogy between heat and mass transfer is adopted to draw out the adiabatic film effectiveness, solving an additional transport equation to track the concentration of CO2 used as a coolant fluid. Both steady and unsteady simulations are carried out: the first one using a RANS approach with k-ω SST turbulence model the latter using a hybrid LES-RANS approach. Regarding uncertainty quantification, three geometrical input parameters are chosen: the hole dimension, the streamwise inclination angle of the holes, and the inlet fillet radius of the holes. Polynomial-chaos approach in conjunction with the probabilistic collocation method is used for the analysis: a first-order polynomial approximation was adopted which required eight evaluations only. RANS approach is used for the uncertainty quantification analysis in order to reduce the computational cost. Results show the confidence interval for the analysis as well as the probabilistic output. Moreover, a sensitivity analysis through Sobol’s indices was carried out which prove how these input parameters contribute to the film cooling effectiveness, in particular, when dealing with the additive manufacturing process.
The increase in air traffic expected in the next years must be accompanied by innovation to ensure the lowest possible environmental impact. Hybrid electric-thermal propulsion systems are currently being investigated and could represent a breakthrough for environmental sustainability in the sector. However, the transition to electric propulsion remains challenging due to the current level of energy density related to storage systems, the additional components associated with power conversion and control systems, not to mention the cost of all the associated equipment. The purpose of this study is to carry out a preliminary assessment of a hybrid propulsion system for a short-mid range aircraft. This study investigates the series hybrid configuration, where a turboshaft, a high temperature superconducting (HTS) electric motor, batteries and power converters interact to provide the necessary propulsion for flight. A zero-dimensional procedure is developed to estimate the mass and efficiency of the powertrain components for a selected flight mission. Thermal engines are modeled with the low-order code and coupled with the components of the electric system through a python routine. A comparison in terms of weight and emissions is reported for the designed hybrid propulsion system and the conventional one. The analysis shows that the weight of the two propulsion systems is similar but, the presence of batteries, even considering a higher level of technology than the current one, leads to a significant increase in the weight of the hybrid aircraft. The second part of the study focuses on pollutant emissions, showing that the hybrid system can reduce CO2 emissions by 58% and NOx emissions by 68% compared to the conventional system. Despite the excellent premise, the reduction in payload for the hybrid aircraft causes a reduction in pollutant emissions per passenger only for NOx. For this reason, further technological improvement is needed to make hybrid propulsion advantageous in terms of both payload and pollutant emissions.
Computational fluid dynamics play a crucial role in the design of cooling systems in gas turbine combustors due to the difficulties and costs related to experimental measurements performed in pressurized reactive environments. Despite the massive advances in computational resources in the last years, reactive unsteady and multi-scale simulations of combustor real operating conditions are still computationally expensive. Modern combustors often employ cooling schemes based on effusion technique, which provides uniform protection of the liner from hot gases, combining the heat removal by means of heat sink effect with liner coverage and protection by film cooling. However, a large number of effusion holes results in a relevant increase of computational resources required to perform a CFD simulation capable of correctly predicting the thermal load on the metal walls within the combustor. Moreover, a multi-physics and multi-scale approach is mandatory to properly consider the different characteristic scales of the several heat transfer modes within combustion chambers to achieve a reliable prediction of aero-thermal fields within the combustor and wall heat fluxes and temperatures. From this point of view, loosely-coupled approaches permit a strong reduction of the calculation time, since each physics is solved through a dedicated solver optimized according to the considered heat transfer mechanism. The object of this work is to highlight the capabilities of a loosely-coupled unsteady multi-physics tool (U-THERM3D) developed at the University of Florence within ANSYS Fluent. The coupling strategy will be employed for the numerical analysis of the TECFLAM effusion cooled swirl burner, an academic test rig well representative of the working conditions of a partially premixed combustion chamber equipped with an effusion cooling system, developed by the collaboration of the Universities of Darmstadt, Heidelberg, Karlsruhe, and the DLR. The highly detailed numerical results obtained from the unsteady multi-physics and multi-scale simulation will be compared with experimental data to validate the numerical procedure.
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