Experimental Study Of The Effect Of Solid Particles On The Coherent Structure Of Turbulent Boundary Layer By PIV

Liquid solid two phase flow is common in chemical,metallurgical,energy and environmental engineering fields.The study of the interaction between particles and turbulence plays an important role in revealing the heat and mass transfer in chemical industry and the treatment of fog and haze in environmental engineering.Image velocimetry(PIV)was used to study the turbulent boundary layer before and after adding particles from the influence of particles on coherent structure in turbulent boundary layer.The spatial characteristics of coherent structures in the turbulent boundary layer of the plate are detected and extracted by Space local mean function combined with new quadrant splitting method and spatial phase averaging method.The influence of particles on coherent structure in turbulent boundary layer is analyzed by extracted the vortex and reverse vortices of the Hairpin Vortex and calculated the probability of occurrence by using spatial multiscale local mean vorticity.The experiment is carried out under the Reynolds numberRe_??12922.The friction velocity of wall is fitted by the mean velocity profile method of turbulent boundary layer,and the friction shear stress and friction coefficient are calculated.The addition of particles increased the resistance of fluid flow,and the resistance increased by 3.57%.The dimensionless mean velocity profile,Reynolds stress profile and turbulence profile were compared before and after the particles were added.It is found that the existence of particles makes the buffer layer thicker in the near wall region,the logarithmic law region of the velocity profile moves upwards,the streamwise turbulence decreases,and the normal turbulence increases.The physical quantities of the coherent structure in the near wall region of the turbulent boundary layer before and after the particle addition were measured and analyzed.In the burst event,the flow velocity is smaller than that before the particle is added,while the normal pulsation speed is the opposite by Comparing the corresponding physical quantities before and after adding particles at the same normal position.The spreading vortex developed because the existence of particles.The presence of particles promotes the occurrence of ejection events,but has little effect on the sweep events by compared the number of ejection and sweep events.Finally,the spatial multiscale local mean vorticity function is used to detect the vortex direction of the Hairpin Vortex and the reverse vortex.Streamwise velocity and streamline topology around hairpin Vortex head vortex head with different normal position and reverse vortex were extracted.The streamwise fluctuation velocity around the spreading vortex were decreased compared to before added particles.The number of vortex eddies before and after adding particles changed little.The normal scale of the Hairpin Vortex head increasing gradually,becoming more and more complete with the increase of the normal position.The number of the vortex head of the Hairpin Vortex shows a decreasing trend with the increase of the normal position.The number of the reverse vortices is always smaller than before the particles are added.The addition of particles reduces the probability of the emergence of the reverse vortexs.