The influence of nose section and turbulence intensity on the flow around thick plates in parallel flow

The flow parallel to thick plates separates in the nose section and reattaches on the flat plate after a certain distance. The flow separation with reattachement causes significant changes of flow, heat transfer and pressure drop. The informations about the flow are recieved from measurements of local mass transfer coefficients, which are fotometrically determined by light-remission. The fundamentals of the measuring technique are based on absorbed ammonia and subsequent chemical reaction with immediate color reaction. The main parameters of flow and related mass transfer are the nose of the plate, the Reynolds-number and especially the turbulence intensity. The measurements were accomplished with plates of a thickness 0.8 mm < s < 91.3 mm of truncated, hemicylindrical and wedge-shaped noses and with cylinders in parallel flow of truncated, hemispherical and conical noses. The measured results indicated, that the flow around thick plates may generally be subdivided into three main forms of the flow: 'boundary layer of flat plate', 'separation bubble' and 'vortex shedding with reattachement'. The critical Reynolds-numbers for the transition of one form to another were determined as a function of the different shapes of noses. For the first time longitudinal vortices can be observed for separation bubbles with significant influence on the flow and on the mass transfer. Thick plates with flow separation and reattachement may be subdivided into three sections: 1. the nose section, 2. the section of separated flow, 3. the section of boundary layer of flat plate downstream of reattachement. For the computation of local mass transfer rates, the position of the maximum mass transfer at the point of reattachement - the dividing line of the 2nd and 3rd section - are determined as a function of the main parameters plate nose, Re-number and turbulence intensity. (orig./HP)