Particle image velocimetry to quantify 3D-flow properties of gas turbine forced mixers

Forced Mixers are typically used in turbofan engines with low and medium bypass ratio to increase the cruise performance and to reduce the jet mixing noise. Most of the design criteria are still based on empirical considerations using qualitative visualisation methods such as smoke injections, or in case of water simulations with dye injection, chemical color reaction and the like. The judgement about the quality of different mixers is therefore based on visual impressions only. Since the flow fields in an engine are highly turbulent, it is nearly impossible to get a representative image of the flow with qualitative measurements. Quantification and subsequent averaging to obtain the steady state flow distribution is a necessity. The techniques used are large scale 2D-PIV to examine the axial, radial and circumferential velocity distribution at specific sections. A conductive method was used to determine the global mixing properties at the beginning and at the end of the mixing section and to deliver an empirical mixing coefficient