Abstract
This paper presents the results of PIV measurements of turbulent airflow in a channel with a single ribbed wall. The rough elements had the form of evenly spaced trapezoids. The ratio of the height of a single rib to the height of the measurement channel was 0.1. The ratio of the distance between adjacent ribs to the height of a single rib (i.e., the w/k ratio) was 5, which suggests a transitional region within the airflow structure between the d- and k- types. The measurements were carried out for the inlet velocity, at which the Reynolds number (Re) was equal to 32,500. The distance to the first rib, at which the turbulent velocity profile is fully developed, was determined. The distribution of the average velocity components, the velocity fluctuation components, turbulent shear stress, as well as the turbulence kinetic energy between two adjacent ribs was presented. The analysis of average streamlines indicated the existence of two vortex structures between the ribs.
Highlights
Turbulent flows in a ribbed channel are present in numerous fields of engineering, such as heat exchange [1,2] turbines [3], maritime engineering [4], and the mining industry [5].The structure of the airflow between two adjacent ribs differs depending on the Reynolds number and the distance between the ribs
When the w/k ratio reaches a certain limit value, the stream becomes reattached between the ribs and a recirculation zone arises downstream of the leeward slope of the rib
After measuring the velocity at the channel inlet, experiments were conducted to determine the distance from the inlet, at which turbulent flow was fully developed
Summary
Turbulent flows in a ribbed channel are present in numerous fields of engineering, such as heat exchange [1,2] turbines [3], maritime engineering [4], and the mining industry [5].The structure of the airflow between two adjacent ribs differs depending on the Reynolds number and the distance between the ribs. Perry et al [6] suggested that the flow between ribs should be divided into a d-type and a k-type flow. The former applies to a geometrical configuration, where the distance between two adjacent ribs is small. In this case, stationary vortex is present in the cavity between the two ribs. When the distance between two adjacent ribs is greater than a certain limit value, the stream on the leeward slope of the rib becomes detached. When the w/k ratio (where “w” is the distance between the ribs and “k” is the rib height) reaches a certain limit value, the stream becomes reattached between the ribs and a recirculation zone arises downstream of the leeward slope of the rib
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