Experiments on a Right-Angled Triangular Notch with Imcomplete Contractions

Abstract

We have experimentally investigated what increment is caused in the coefficient of discharge for a triangular notch when the width of the channel of approach is not ample. The experiment was carried out under the instructions of Professor I. Oki who wrote an article entitled "Some Considerations on a Triangular Notch with Incomplete Contractions" (Journal of the Society of Mechanical Engineers, Japan, Vol.35 No.180,Apr.1932 p. 280.) The apparatus which we used consists of a thin edged right-angled triangular notch fitted at the end of the channel of approach of 30 cm wide in the first series of experiments and of 20 cm wide in the second series. The channel is 55 cm deep and 552 cm long. The volume of water passed over the notch was determined by means of calibrated tanks and the head was measured by a hook gauge. The results of experiments of the first series are shown in Fig.7 and of the second series in Fig.8 in the report (written in Japanese). Throughout the experiments we have noticed that when the head is very low the water clings to the edges of the notch and the discharge is greatly increased. If the down-stream side of the notch plate be coated with paraffin wax the stream contracts very finely, so that the coefficient of discharge becomes very small. For these two cases in each series of experiments we determined that the increment of discharge coefficient was due to the incompleteness of the side contractions, and concluded that the expression for correction of the discharge coefficient due to the incomplete contractions proposed by Professor I. Oki was nearly true within the limits of our experiments.