Gas turbine systems operate on the ideal thermodynamic cycle (consisting in two isentropic and two isobars) represented by Brayton cycle. The real Brayton cycle consists in quasiadiabatic expansion and compression processes, but unisentropic, and the heat transfer processes are not isobar processes, due to flow pressure losses. In addition, the air and hot gases are not perfect gases and not have the same flow rates. Brayton cycle thermal efficiency depends on: compression ratio; ambient temperature; air temperature at turbine inlet; compressor efficiency and turbine components efficiency; blade cooling requirements; increased performance systems (exhaust gases heat recovery, intercooling, intake air cooling, afterburning imple
The ability to predict the dynamic behaviour of a gas turbine is of great importance, even from the early design stages, as it impacts the designer’s ability to select higher performance operating regimes while maintaining the gas turbine within the required safety margins, inside stable operation envelope. Most of the models used for numerical simulations of the dynamic response of a gas turbine are based on the turbine characteristic curve, determined, in most cases, for the steady operating states of the gas turbine. From a manufacturing standpoint, the geometrical accuracy of the machined blade profiles is a major concern, as it strongly impacts on the actual gas turbine performance. Even relatively small deviations in the shape of the axial turbine blade profile affect the value of the area of the channel between two adjacent turbine blades minimum section, and, thus, impacts significantly upon of the actual gas turbine performance. With this in view, this paper aims at studying the influence of the thermal expansion history on the axial turbine characteristic curve. The thermal expansion that occurs between the temperature defining the idle operating regime and the temperature defining the maximum stable operating regime usually takes about 30 minutes, while the gas turbine acceleration process from idle to the maximum stable operating regime takes between four to eight seconds. Due to the thermal expansion, the minimum area of the channel between two adjacent turbine blades (a.k.a. the throttle area) increases by about 1.5% when the gas turbine moves from idle to the maximum stable operating regime, change that affects significantly the turbine characteristic curve. Hence, the deviation of a turbine characteristic curve due to the thermal expansion history must be taken into account in order to improve the gas turbine dynamic behaviour prediction. To demonstrate this improvement, this paper will present two numerical simulations. In the first case, the simulation reproduces the turbine characteristic for nominal regime. In the second case, the turbine characteristic at dilatation state at idle regime. The results of the numerical simulation are compared against each other in order to highlight the differences in the two turbine characteristics induced by the thermal expansion history.
Turbo-engines with known performances reaching the end of their useful flying life can become useful assets in the execution of industrial projects. One such project reported in this paper is to install a high capacity complex device which will clear out the water in cases of floods. The partnership created in order to accomplish the task includes specialists in energetic, turbo-machinery, amelioration, hydraulic and action logistics fields and is aiming to acquire knowledge, results and experience and to transfer the information to economic and social environment. The TV2-117A turbo-shaft is the main component of the power group representing the energy source of the installation. It is connected to a reducer gear-box and a high capacity water pump. Considering the purpose of the installation to be realised, a device destined to handle natural calamities effects, the solution must fulfil several very important conditions: mobility, power and reliability. Being known the fact that moving elements have lower reliability conducts to the idea of an oil cooling system without mechanical or electrical driven fans. This is possible through using the ejection effect in a system based on the exhausted hot gases from the turbo-engine. The ejection device is a tubular structure using three concentric tubes on the outlet. The central one absorbs the hot gases and drives the cool air from the surrounding environment through the other two to accomplish both the oil and turbo-engine box cooling. The numerical analysis, using a CFD code, is still in progress and the paper presents intermediate results. The CFD conditions were imposed by the turbo-engine experimental data obtained in previous tests and the known working conditions established for the device to be created. The preliminary results helped to eliminate many flow problems caused by geometric dimensions and to establish the necessary adjustments in order to obtain the expected mass flow and speed values for the cooling devices. The adjustments on the geometry consisted in modifying the lengths, the bending and the diameters of the tubes. The final and most suitable geometry is still to be determined using the CFD code.
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