Effective Parameters on Formation of Undular Flow on the Broad-Crested Weirs

Undular flow on broad-crested weirs is a phenomenon occurs under certain hydraulic conditions. In this case the flow surface on the weir transforms to a sinusoidal wave and the number of waves may vary from one to over 10. Forming of this phenomenon leads to error in measurement of flow discharge by weirs. In this study in addition to introduction of the most effective parameters on undular flow formation، effect of geometric properties of rectangular broad-crested weirs was also investigated when only one wave formed. The results show that reducing the upstream slope from standard angle to 21 degree، decreases the relative wave height by 78 percent and increases the relative wave length by 55 percent. The position of undular wave also displaced toward the downstream. With changing in upstream edge shape from sharp edge to a relative radius of curvature equal to 0. 5، the relative height of wave decreased up to 80 percent. Roughening the surface of the weir crest led to attenuation and elimination of undular wave، depending on the position of roughness surface.