Abstract
The behavior of confined water jet under free surface has been examined.
The jet does not flow straight. The water above the upper part of the jet is surrounded by a free surface, two cover plates, the nozzle block, and the jet, while the water below the lower part of the jet is not confined. A water bubble region generates in the upper part because of the entrainment effect of the jet. The pressure in this region will be lower than the static pressure. Therefore, the jet deflects towards the free surface, but its condition is not always stable. When the jet velocity becomes larger than a critical value, the whole water in the upper part of the jet is entrained into the jet and the fluid in this area turns into air. Then the jet deflects in a stable manner towards the free surface. The phenomenon in this case is similar to Coanda effect.
The critical velocity of the jet increases as the distance from the free surface to the nozzle exit becomes longer, while it decreases as the nozzle width becomes larger. The attachment length of the jet becomes longer with the increase of the jet velocity.
