Design of Gas Turbine Package Ventilation System by Scale Model
1.1 General Topics on Fan Design
Gas turbines are usually installed inside an enclosure in order to isolate the engine and the package from the surrounding environment and to reduce the noise emissions. A ventilation system is so required to keep temperature under acceptable limits and to dilute any hazardous accumulation of gas due to unexpected leakages.
CFD analysis is the common instrument used to assess the behavior of the flow, in terms of flow path, temperature distributions and velocity field. In this work, a scale model (1:8) of the real configuration was created to perform a detailed experimental 3D assessment of the entire aero-derivative GT package. The common 3D CFD study might not necessarily include all details during the design phase, since the volume of the original package can be around 60 m³ and the geometry can be extremely complex for the presence of pipes, valves, instruments and various equipment.
The scale model, built using sintered plastic material through rapid prototyping, was used for a test campaign reproducing the operation of the ventilation system, copying the dynamic similarity of the real scale. The model was equipped with a set of instruments to acquire measurements of pressure and velocity in several locations, at different flow rates. A significant benefit of using a scale model is to optimize the ventilation system carrying out fast and less expensive tests, compared with the activities usually needed at the test bench for the real package (scale 1:1).
The outcome of this experimental investigation is the confirmation that the CFD studies currently performed are accurate and reliable enough to provide an accurate prediction of the flow field inside the entire package; at the same time, a new and versatile methodology of investigation has been developed and it can be used in future studies to optimize the ventilation system of new packages.