生物膜泥沙床面对水体紊动影响的实验研究

泥沙床面生长生物膜后水流紊动特性将发生变化,进一步影响到泥沙的起动,悬浮和输移特性。本文采用d500.1 mm的天然沙,对相同水流条件下无生物膜生长和有生物膜生长床面以上的水流内部结构进行研究。实验中采用多普勒声学流速仪(ADV)测量了垂向流速,对比分析了生物膜生长前后,时均流速、雷诺应力、紊动强度以及紊动猝发事件在垂向上的变化,并初步分析了这些变化对泥沙运动的影响。结果表明:生物膜生长后,同流量条件下的垂向平均流速增加,床面阻力减小;对比无膜沙床面,有膜沙床面在发生冲刷的水力条件下,雷诺应力、紊动强度均有所减小,从而会影响到悬沙的浓度分布;同时猝发事件发生率在垂向上的变化也使得生物膜泥沙床面的泥沙起动更加困难。

Changes in the turbulent characteristics for sediment bed coated by biofilm

Biofilm growth on the sediment bed will change the turbulent characteristics and influence the sediment incipient, suspension and transportation. In this study, sediment with median size d₅₀<0.1mm is used to investigate the change of turbulent characteristics with and without biofilm coating on the bed under the same discharge. Acoustic Doppler Velometer(ADV) is used to obtain the instantaneous velocity in the vertical direction. Mean velocity, Reynold stress, turbulent intensity distribution and bursting events above the bed are analyzed and compared between the biofilm-coated bed and the bed without biofilm,the influence of which on the sediment transportation is also discussed. Results show that with biofilm coated, the mean velocity in vertical direction increase and the bed resistance decrease, Reynold stress and turbulent intensity also decrease near the bed, which may change the vertical distribution of suspended sediment. Bursting events analysis shows a disadvantage of sediment incipient by the coated biofilm.