No abstract

Transverse jets have been the subject of study for several decades due to their relevance in a number of flows in nature and engineering applications. The momentum flux ratio J, is generally considered to be the leading independent parameter and has been explored extensively over a nominal range from unity to several hundred. The current study considers the flow field of a transverse jet at J values significantly smaller than unity, 0.0013 ≤ J ≤ 0. A modulated absorption/emission thermometry (MAET) technique under development at the Air Force Research Laboratory (AFRL) requires a narrow film barrier to maintain a clean optical access window. A low momentum flux transverse jet is used to limit penetration into the crossflow and avoid corruption of the optical measurement. Particle image velocimetry (PIV) was used to investigate the jet and crossflow interactions near the jet exit. A laminar jet was injected into turbulent channel crossflow. Under low momentum flux conditions, the crossflow has sufficient local momentum near the injection location, that it is ingested into the jet hole. It was expected that this would increase the effective momentum flux of the jet, which would lead to an increased J and increased penetration into the crossflow. The complex 3-dimensinoal interaction however, suggestspenetration is far reduced for the lowest J values studied. The two smallest J values were found to penetrate the least into the crossflow. These two cases were also found to have the highest levels of unsteadiness and a pulse-like behavior which created localized regions of increased velocity nearly 1D j into the crossflow. These results help tailor the specific film flow requirement for the MAET technique under development at AFRL. Nomenclature D j= jet diameter f = frequency h = height h c = channel height J = momentum flux ratio l = length M = blowing ratio Q = cross-correlation peak ratio u = streamwise velocity u j = mean jet velocity