Gas turbine packages require a ventilation system in order to keep temperatures under acceptable limits and to dilute any hazardous accumulation of gas due to unexpected leakages. As part of the design phase, a detailed CFD (Computational Fluid Dynamics) analysis is performed on the complete system to assess the fluid dynamic behavior of the flow in terms of flow path, temperature distributions and velocity field.
In this work, as additional approach, a detailed experimental 3D assessment of an entire aero-derivative gas turbine (GT) package was performed by creating a scale model (1:8) of the real configuration. The original package can be as much as 60 m3 in volume where details from pipes to valves can create severe flow distortions and the 3D CFD study might not necessarily include all details up to such level during the design phase. 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 and at different flow rates. A significant benefit of using a scale model with transparent plexiglass for the external structure of the enclosure and ventilation ducts walls, was that it allowed to carry out a smoke test. This has been done by injecting a visible gas from several locations allowing the visualization of the streak lines of the local flow field. The aim of this approach was to find a fast and reliable way to investigate in detail complex phenomena such as gas leakage dilution and local flow distribution.
A good agreement between experimental and computational data was found confirming that the CFD studies currently performed during the standard design phase are accurate and reliable enough to provide a proper prediction of the flow field inside the entire package even when a high level of details is included.