Experimental investigation of inertial particle transport in a turbulent boundary layer

Abstract

The first major part of the work was to commission and test the newly built 3 meter openchannel experimental rig. Various development stages have been carried to improve the design specifications to meet experimental requirements. The original 2 meter open-channel working section was replaced with a new 3 meter channel working section enabling measurements to be taken further downstream allowing the boundary layer to develop. The original bell mouth inlet was replaced with a hyperbolic tangent profile 3:1 contraction with a honeycomb, coarse and fine gauzes fitted upstream. 25% porous perforated plates were installed at the channel exit and also within the inlet plenum tank to reduce the turbulence level. LDV measurement in the freestream revealed that the turbulence level is below 1% and the boundary layer profile collapses well with DNS data of Schlatter (2010). A dip in the outer wake region of the velocity profile can be observed throughout the measurements and is attributed to the aspect ratio of the channel which is 1.7 at Fr = 0.33. Nevertheless, boundary layer profile and turbulence intensity profile collapse well with published DNS data. Good agreement was obtained between measurements carried out using the available LDV and time-resolved PIV systems. Time-resolved PIV measurements were performed in a dilute particle-laden flow, tracking nearly neutrally buoyant polymer microspheres within the measured velocity field of a near wall turbulent boundary layer. Data were taken 2100mm downstream of the inlet, in a vertical light-sheet aligned in the streamwise direction on the centerline of the horizontal, open-channel channel facility. High frame-rate measurements were taken to temporally and spatially track particle motion and instantaneous visualization clearly reveal a link between particle movement and near-wall coherent structures. Structures having 2D vorticity signatures of near-wall hairpin vortices and hairpin packets, directly affect particle motion. Statistical and instantaneous results agree well with published experimental and numerical work. Conditional statistics were investigated for the particles using the Quadrant method. Particles moving outwards from the channel floor are influenced by the Quadrant 2 ejection events and those that moves inwards towards the wall are influenced by the Quadrant 4 sweeps events. v Particle-fluid velocity correlations, rpf were calculated for each particle trajectory and averaged of all the particle-fluid velocity correlations, R, were determined for the whole dataset for Re=1000. This value is estimated to be 0.0261 and 0.000643 respectively for the particle-fluid streamwise and wall-normal velocity correlation.