Measuring the flow through a model engine inlet system containing a plenum and runners

This paper describes an experiment carried out in a model of an inlet system containing a plenum chamber and runners. Such inlet systems are commonly found on petrol internal combustion engines where the cylinders are arranged in a V-configuration. Measurements of velocity, turbulence intensity and pressure drop across the system have been made and a detailed error analysis carried out. These measurements are suitable for the validation of results obtained from computational fluid dynamics (CFD) software. Particular attention has been paid to reducing turbulence intensity levels at the inlet of the system, with additional entry lengths and smooth bell-mouth profiles being used. At each measurement point the laser Doppler anemometry (LDA) system has been tuned by hand to improve measurement sensitivity. Seeding of the flow has been an important factor and water droplets produced by a medical nebulizer have been used. Errors in velocity measurement vary throughout the flowfield, with a strong dependency on turbulence levels. From the results a relatively simple three-dimensional flow structure is found with the inlet flow separating on entry to the plenum, forming a ring vortex with a central jet within it. This jet turns from the horizontal to the vertical to enter the open runner, forming a separation bubble on the upstream side of the runner. A large slow-moving recirculation region forms in the plenum downstream of the open runner. From measurements of turbulence intensities, large values of around 40 per cent are found at the plenum-runner interface and in the recirculation region. This means that the flow is essentially time dependent even for notionally steady state conditions.