The blades of a turbomachine comprise airfoils, which are bent such that the lean angle, defined as the angle which the stacking line of the airfoil includes with the radial direction, and measured in the direction of rotation, is variable along the width of the flow channel and decreases from the hub towards the housing. The method comprises providing a gas-liquid interface, providing a laser source and generating a beam comprising a sequence of laser pulses, and focusing the beam to a target location within the liquid at a predetermined distance from the gas-liquid interface and creating a plurality of cavitation bubbles, yielding a jet directed away from the gas-liquid interface. Discharge passages having the same length are connected with the openings, respectively.