THE TURBULENCE STRUCTURE OF THE ANNULAR NON-SWIRLING FLOW PAST AN AXISYMMETRICAL POPPET VALVE

This paper describes an experimental investigation of the non-swirling flow through an axisymmetric port and poppet valve assembly under ste ady flow conditions using laser Doppler anemometry. The three velocity components and the associated Reynolds stresses were measured by ense mble-averaged techniques and the turbulence kinetic energy and its pro duction rate were determined. Time-resolved measurements were also tak en in order to determine turbulence time and length scales and the dis sipation rate of the turbulence kinetic energy. The Reynolds number, b ased on the minimum cross-sectional area of the port, was 25 000. The flow is characterized by an annular jet which forms two vortices, one on either side of the jet. A jet flapping instability is also evident since the skewness and kurtosis of the velocity probability distributi on function depart from the Gaussian form. This instability causes an intermittent mixing between eddies in the jet region and the vortices which introduces a non-turbulent contribution to the measured quantiti es. The production rates of the turbulence kinetic energy were found t o be negative in some regions of the flow, indicating counter-gradient transport of momentum by turbulence: according to the coherent struct ures approach, the distribution of the Reynolds shear stresses and the length scales in these regions imply possible changes in the orientat ion of eddies.