Four-sensor hot-wire probe measurements of the isothermal flow in a model combustion chamber at different levels of swirl

Measurements of the isothermal flowfield in a model combustion chamber at three different levels of swirl were carried out with a four-sensor hot-wire measurement technique. The new four-sensor hot-wire probe allows the measurement of all three components of the instantaneous velocity vector simultaneously at high data rates. The three mean velocity components and all six Reynolds stress components are subsequently calculated from an appropriate number of instantaneous-velocity measurements. The four-sensor measurement technique is described in the first part of the paper. The main feature of the flowfields measured is the existence of two distinct regions: a supercritical region in which disturbance do not influence the upstream flow and a subcritical region in which disturbances have a strong upstream influence. The transition from the supercritical flow at the inlet of the combustion chamber to the subcritical flow is associated with vortex breakdown and the formation of recirculation zones. With increasing swirl strength, the flow in the subcritical region approaches a one-dimensional state; that is, the mean velocity components are a function of only the radial' coordinate. Measurements of the Reynolds stress components are consistent with the mean velocity measurements. In the subcritical flow region the turbulent momentum transport nearly vanishes; similar to the mean velocities, the turbulent intensities approach one-dimensional behavior in the subcritical flow region.