Head losses and flow field at trash racks

Abstract

The purpose of this master thesis was to measure the head loss caused by fish-friendly trash racks in an open water channel and to measure the turbulent flow field around its bars. Angled model trash racks with different bar arrangement and orientation were tested, accompanied by a bypass. As a part of the master thesis a literature review was done with special focus on the turbulent flow field around bars and on different equations used for head loss prediction. Experiments were carried out at the NTNU hydraulic laboratory in a straight open channel. Head loss measurements were carried out for six racks at six different discharges. The measurements related to the turbulent flow field were carried out by the V3V PIV system from TSI Inc. in vicinity of the bars downstream and upstream of the trash racks. The results showed that horizontally barred racks overall performed better than trash racks with vertical streamwise and inclined bars with regards to head loss. The results also provide detailed volumetric velocity distribution plots in vicinity of the bars. Head loss predictions were made on the basis of several head loss equations. The head loss equations were able to predict the actual head losses to a certain degree, but further studies are needed to fully determine the effects of angled trash racks and bypasses on head losses. Further studies on trash racks with horizontal bars are also suggested.