Modifications of coherent structures in a turbulent boundary layer of dilute gas-particle horizontal channel flow were experimentally investigated by means of simultaneous two-phase PIV(particle image velocimetry)measurement.The measurements were conducted in the near-wall region at Reynolds number of 430 based on the wall friction velocity and half channel height.Polyethylene beads with the diameter of 110 μm were used as the dispersed phase

and three low mass loading ratios ranging from 10-4 to 10-3 were tested.Spatial two-point correlations of fluctuation velocities and quadrant analysis were adopted to examine the change of characteristics of turbulent coherent structures in the lower boundary layer.It was found that the addition of particles noticeably modified the turbulence structures in meso-scale near the wall event at mass loading ratio 0.025%

thereby affected the gas-phase turbulence characteristics in macro-scale

e.g.fluctuation velocities and Reynolds shear stress etc.Particle sedimentation increased the roughness of the bottom wall

which significantly enhanced turbulent bursting in the inner region of the boundary layer.And then the wall-normal fluctuation velocity and Reynolds shear stress were both increased in the viscous sublayer.Under the effect of particle-wall collision

the Q2 events(ejections)of gas-phase were slightly increased by particles

while the Q4 events(sweeps)were obviously decreased.In addition

the spatial scale of the wall structures also remarkably shrink under the intensified crossing-trajectory effects due to particle saltation near the bottom wall.Consequently

the presence of the particles suppressed the turbulent coherent structures in the outer region of the boundary layer

which resulted in significantly decreasing wall-normal fluctuation velocity and Reynolds shear stress of the gas-phase above the viscous sublayer.Particle inertia changed the viscous sublayer of gas turbulence with a smaller thickness and a larger streamwise velocity gradient

which increased the peak value of streamwise fluctuation velocity of the gas-phase with its location shifting to the wall.