Abstract: Fluid jet apparatus and method for cleaning material from the inside of a tubular conduit utilizing a cleaning head that lies adjacent to one wall of the conduit and includes at least two fluid jet forming means for directing a plurality of high pressure fluid cutting jets in a forward direction and at an acute angle relative to the axis of the head and the conduit so that they are directed toward the opposite wall of the conduit. The cleaning head is rotated around and remains adjacent to the wall of the conduit and is advanced into the conduit as the jets cut away the material whereby the fluid jets create an asymmetric cutting pattern on the surface of the material and the counter thrust of the fluid jets keeps the cleaning head offset relative to the axis of the conduit and against the wall of the conduit to provide passage for removal of the cut material and spent fluid away from the cutting area and out the end of conduit.

Abstract: Process and apparatus for enhancing the erosive intensity of a high velocity liquid jet when the jet is impacted against a surface for cutting, cleaning, drilling or otherwise acting on the surface. A preferred method comprises the steps of forming a high velocity liquid jet, oscillating the velocity of the jet at a preferred Strouhal number, and impinging the pulsed jet against a solid surface to be eroded. Typically the liquid jet is pulsed by oscillating the velocity of the jet mechanically or by hydrodynamic and acoustic interactions. The invention may be applied to enhance cavitation erosion in a cavitating liquid jet, or to modulate the velocity of a liquid jet exiting in a gas, causing it to form into discrete slugs, thereby producing an intermittent percussive effect.