An experimental investigation of the effect of inlet velocity and turbulence profiles on the development of turbulent flow in diffusers

Conical diffusers find many applications in internalflow systems. In some of these, for example wind tunnelsand process plants, the entry conditions may be a uniformvelocity low turbulence profile or one similar to a fullydeveloped pipe flow. In others, downstream of industrialgas turbines for example, the profiles may be highly turbulent and non-uniform.Priest(30) has recently established the diffuser 000 performance for included angles of 5 , 8 and 15 , arearatios 2.5 and 5, over the full range of a developing turbulent pipe flow.The work described below is the first attempt in aninvestigation to examine the effects of velocity andturbulence profiles in general on conical diffuser perform-ance. The initial aim is to vary the turbulence intensitywhile keeping the velocity profile uniform and then to varythe velocity profile, keeping the turbulence intensity aslow as possible For this preliminary investigation attention has beenconfined mainly to a single diffuser of gO included angle area ratio 2.5 so that maximum effort could be employedinvestigating the feasibility of generating velocity andturbulence profiles of the kind described above. At thisstage too, the turbulence has been characterised in thesimplest possible way, by the axial intensity alone.