摘要
通过水槽试验研究了有屈服应力的粘土泥浆明渠流的湍流结构和脉动流速的统计特性及紊动漩涡的频谱结构.如采用考虑了屈服应力的雷诺数R_(em),则R_(em)<2000为完全层流,R_(em)=2000—8000为过渡湍流.处于过渡湍流区的泥浆流下部为湍流,同时中、上部部分流层持续地或间断地保持层流状态.在空间上,过渡区湍流可以划分5层,即:近壁层流层、间歇湍流层、强紊动层、扩散层和表面层,其中间歇湍流层相当于牛顿体湍流的粘性底层.间歇紊动是泥浆过渡区湍流的重要特性.间歇湍流层和扩散层的泥浆流速忽而脉动,忽而恢复层流.间歇湍流层的紊动有规则地间歇,说明泥浆湍流底层可能也存在着间歇性的粹发现象.
The turbulent structure,the statistical characteristics of fluctuating velocity,and the spectral density distribution of turbulent eddies in Bin-gham fluid in open channel flow are experimentally studied.Development of Bingham fluid turbulent flow goes through the following stages:(1) Laminar flow;(2) Transitional turbulent flow;and (3) Turbulent flow.The critical Reynolds number Rem for transition from laminar flow into turbulent flow is similar to that in Newtonian flow,but the definition of Rem is different,the former consists of the yield stress tB and the rigidity coefficient η In the transitional stage,Bingham fluid in open channel flow is turbulent in the lower part while it remains laminar in the upper part of the flow.There is a laminar sublayer in the zone 0<y+<1 It could be rather thick if tB and 77 are quite large.Five layers characterized by different turbulent intensities and different intermittent turbulence coefficient could be recognized,i.e.(1) Laminar sublayer;(2) Intermittent turbulent layer;(3) High-intensive turbulent layer;(4) Diffusion layer;and (5) Surface layer.The intermittent turbulent layer (1<y+<5) is similar to the viscous sublayer in Newtonian turbulent flow.Flow in the intermittent turbulent layer maintains laminar for a while,then suddenly changes into turbulent flow,several tenths of secnd laterit recoils back to laminar flow,......The regular intermittent turbulenceinterpretes intermittent bursting process in this layer similar to that in Newtonian turbulent flow.
出处
《水利学报》
EI
CSCD
北大核心
1992年第12期9-17,共9页
Journal of Hydraulic Engineering
基金
国家自然科学基金
