Measuring the flow through a model engine inlet system containing a plenumand runners

This paper describes an experiment carried out in a model of an inlet syste m containing a plenum chamber and runners. Such inlet systems are commonly found on petrol internal combustion engines where the cylinders are arrange d in a V-configuration. Measurements of velocity, turbulence intensity and pressure drop across the system have been made and a detailed error analysi s carried out. These measurements are suitable for the validation of result s obtained from computational fluid dynamics (CFD) software. Particular att ention has been paid to reducing turbulence intensity levels at the inlet o f the system, with additional entry lengths and smooth bell-mouth profiles being used. At each measurement point the laser Doppler anemometry (LDA) sy stem has been tuned by hand to improve measurement sensitivity. Seeding of the flow has been an important factor and water droplets produced by a medi cal nebulizer have been used. Errors in velocity measurement vary throughou t the flowfield, with a strong dependency on turbulence levels. From the re sults a relatively simple three-dimensional flow structure is found with th e 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 plenu m downstream of the open runner. From measurements of turbulence intensitie s, large values of around 40 per cent are found at the plenum-runner interf ace and in the recirculation region. This means that the flow is essentiall y time dependent even for notionally steady state conditions.