  In this paper, we have experimentally, numerically and theoretically
investigated the water jet cleaning process. Very high speed water jets
(~80-200 m/s) are typically used in such cleaning operations. These jets
diffuse in the surrounding atmosphere by the process of air entrainment and
this contributes to the spreading of the jet and subsequent decay of pressure.
Estimation of this pressure decay and subsequent placement of the cleaning
object is of paramount importance in manufacturing and material processing
industries. Also, the pressure distribution on the cleaning surface needs to be
assessed in order to understand and optimize the material removal process. In
an industrial setting, experimental study is performed to formulate the
pressure characteristics. It has shown that the decay of stagnation pressure
along the axial direction is linear. It also revealed that no cleaning is
possible at radial locations greater than 1.68D from the centerline. Numerical
simulations are performed to capture the process of air entrainment in the jet
and the subsequent pressure characteristics. The simulation results are found
to correctly predict the experimental data. Moreover, a theoretical model for
evaluating the optimal and critical stand-off distances has also been derived.
Based on our results, we found that the optimal stand-off distance in cleaning
operations is ~5D and the jet looses its cleaning ability at axial distances
greater than ~26D.
