High frequency aero-acoustic noise is a prominent issue with turbocharged small displacement engines. Currently, no approved methodology exists to predict this noise contribution. This presentation outlines an empirical based method to predict aero-acoustic noise generated from various tailpipe geometries. Using cold-flow bench testing and CFD analysis, it was found that high frequency sound pressure levels vary logarithmically with turbulent kinetic energy. This established transfer function, which accounts for noise sources from dean vortices and the turbulent exit wake, can be used to predict aero-acoustic noise for new tailpipe geometries.
Design guidelines for a representative mass flow rate at room temperature were also derived to aid in minimizing aeroacoustic noise in tailpipe geometries. It was found that the critical design criterion is the bend ratio (BR), which is the radius of curvature divided by the pipe radius (Rc / r). For 1.75in diameter pipes, BR should be > 4.3 while 2.25in and 2.75in pipes should have a BR > 3. Continued work is expected in this area of study as the sample size of pipe geometries and ambient conditions tested will expand.