Determination of the critical Shields number for particle erosion in laminar flow

We present reproducible experimental measurements for the onset of grain motion in laminar flow and find a constant critical Shields number for particle erosion, i.e., theta (c)=0.12 +/- 0.03, over a large range of small particle Reynolds number: 1.5x10(-5)<= Re-p <= 0.76. Comparison with previous studies found in the literature is provided. (c) 2007 American Institute of Physics.