Flow Visualization Around Small Roughness Elements With Hydraulic Scale-up Model Based On Re-Fr Similarity Law

Hydraulic model test provides a useful method for us to simulate the real water environment,which is constructed and operated at a reduced scale and offers an alternative for examining coastal phenomena.Meanwhile,hydraulic model combines with PIV(Particle image velocimetry)method,which is a whole field,nonintrusive,indirect velocity measurement technique can obtain the velocity information with high accuracy and temporal and spatial resolution by transferring the velocity information of the flow to the velocity information of tracer particles based on algorithms.The research area of my experiment is the boundary layer areas around the roughness surface of artificial reefs.And the motivation behind the present research is to focus on the flow visualization of simultaneous flow field information around small roughness elements by following Re-Fr similarity law.Meanwhile,we also want to find the difference of the results among Re-Fr similarity law,Reynolds similarity law and Froude similarity law.To use Re-Fr similarity law,the relationship between kinematic viscosity and concentration should be taken into consideration.Therefore,I used CMC(Carboxymethyl cellulose)as the viscous materials to change the kinematic viscosity of solutions.and falling sphere method to find the proper relationship between kinematic viscosity and concentration of CMC solutions.Then,I did the experiments about flow visualization around small roughness elements by following different similarity law.I totally have three groups:Reynolds similarity law group,Froude similarity law group and Re-Fr similarity law group.In each group there are three different conditions,therefore,I have totally 9 cases.In each case,I have more than 4500 frames of Re-Fr similarity cases and more than 6000 frames of Reynolds similarity law cases and Froude similarity law cases.The frame rate of each case changed from 1/100s to 1/1000s based on the velocity of the flow.Normally,the higher velocity the smaller frame rates will be used in the experiments.Then,I depicted the flow fields around the surface of roughness elements and analyzed the velocity profile of horizontal component of five different positions around the roughness elements.The results of the whole experiments are shown as follow:1.The relationship between the kinematic viscosity and concentration of CMC solution follows:vcmc=Vwater ×(1+4.5 × 108 × Ccmc204)2.The tendency of the flow fields and the thickness of boundary layer around the roughness element are similar among different similarity law but details are different.3.Velocity gradient and boundary layer thickness are affected by the similarity laws.Bigger Reynolds value gives smaller velocity gradient and thicker boundary layer.Bigger Froude value gives bigger velocity gradient and thinner boundary layer.4.Vortex flow:In crest areas,vortex flow only appears in Re-Fr and Fr similarity law cases.In the trough areas,the return flow appears in all cases...