Preliminary Study On The Failure Conditions Of Nonorthogonal Weir

Hydraulic is the primary condition which is indispensable in modernization.Recently lots of small reservoir projects were constructed in our country, however, withthe limitation of the early construction technology, economic conditions, reservoir sluicefacilities of weir without sluice control caused smaller reservoir capacity, inadequatereservoir benefit or even the insufficient flood discharge capacity. The nonorthogonalweir is not orthogonal to flow direction at plan layout (oblique weir), And its maincharacteristic is that the overflow length can be extended several times or more than tentimes longer than the orthogonal straight weir with the same river width. Uaually thedischarge capacity is proportional to the overflow length, therefore the fomer increasesthe same as the latter. Nonorthogonal weir greatly increases water discharge but notunder any condition. Compared with orthogonal weir, the discharge capacity ofnonorthogonal weir will not be increased or did not increase under the particular weirstructure or flow condition, this phenomenon is called failure state or failure conditionwhich should be avoided in practical engineering. Therefore, study on the failurecondition of nonorthogonal weir is of great significance in practical engineering.Based on the generalized experiment and three-dimensional numerical simulationmethod, this paper preliminary study the discharge capacity and failure conditions ofnonorthogonal weir, the main research conclusions are as follows:(1) By generalized flume experiment on orthogonal and nonorthogonal weirs aswell as the variation of water surface profile and flow condition, it focuses on theinfluences of nonorthogonal weirs’ angle, weir type, flooding degree to the dischargecapacity.(2) In order to explore the reasons of failure state profoundly under the limitationsof generalized experiment, this paper selected typical conditions in physical model test,applying FLUENT3D numerical simulation to calculate flow on weir. The consistentresults of flow field distribution and water surface profile achieved from numericalmethod and physical modes verify the feasibility and rationality of the numericalmethod.(3) Combined with the results of numerical simulation and failure conditions ofnonorthogonal weir obtained from generalized physical model, it comprehensivelyanalyzes the characteristics of flow field, weir angle and submergence degree and so on,to get the basic failure conditions of nonorthogonal weir. (4) In the view of possible failure state on nonorthogonal weir, and the results ofgeneralized physical model and numerical simulation, the failure conditions of obliqueweir are as follows:(a) for non-submerged flow, the oblique angle≤30°;(b) forsubmerged flow, the weir type of oblique angle＞30°in large flow and highsubmergence degree conditions, will gradual failure state. And this paper shows thatlabyrinth weir will not fail.