U380351.pdf (84.02 MB)
Turbulence effects in internal airflows.
thesisposted on 2015-11-19, 08:58 authored by Colin Ingram. Bradley
The effect of inlet conditions on the performance of conical diffusers is considered. The conditions at inlet which were independently varied are the cross-sectional time-meaned velocity distribution and the associated stream turbulence variation. The investigation formed part of a research programme on interaction effects between pipe and duct components. Sources of data on the effect of such variants include Kline, Winternitz, Livesey, Miller and Cockrell amongst others. Whereas these persons considered the symmetrical profile developments accompanying varying inlet pipe lengths and Reynolds numbers, Tyler and Williamson examined the effects of distorted time-mean velocity profiles at inlet. A very limited amount of experimental work has been published by Kline et al on the effect of varying the free stream turbulence intensity at the diffuser inlet when the associated boundary layer thickness is small. The thesis considers this previous work, then describes the development of a turbulence generator with which a mean velocity distribution, barely distinguishable from fully-developed flow is obtained in a few pipe diamters. This mean velocity is accompanied by a turbulence intensity which is capable of being increased up to three times that normally associated with fully-developed flow. Conical diffusers were mounted downstream of the turbulence generator and pressure recovery characteristics over a wide range of expansion angle and area ratio were obtained. In general the results show a significant increase in pressure recovery over values associated with normal fully-developed inlet flow. An integral computational method is developed for ducts, pipes and conical diffusers which leads to successful predictions of boundary layer growth and diffuser pressure recovery for a wide variety of inlet boundary layer thicknesses. Possible extensions of this method to admit inlet turbulence level as a parameter which influences diffuser pressure recovery are considered. The thesis discusses how variations in mean velocity profiles and turbulence levels at the diffuser inlet are significant parameters in the current industrial context.
Date of award1970-01-01
Awarding institutionUniversity of Leicester