Effect of the nozzle structure of the large-diameter slurry shield cutterhead on the scouring characteristics

Abstract

The mud cake of the large-diameter slurry shield severely affects the tunneling efficiency and construction safety, the avoidance and elimination of which largely depends on the scouring characteristics of the nozzle. Based on the solid–liquid two-phase flow theory and dynamic mesh technology, this paper establishes a mud flow model of the nozzle on a slurry shield cutterhead and a cutterhead rotation model and builds a simulation model of the cutterhead nozzle scouring process with CFD. By verifying the simulation model with the self-developed 1 Mpa pressure-bearing scouring test bench, the paper conducts an analysis on how the convergence angle, outlet diameter, and length–diameter ratio of the 12 m large-diameter slurry shield cutterhead affect the scouring characteristics of the nozzle. The results show that when the convergence angle is 13°, the flow fields will be more uniformly distributed inside the nozzle, the average flow rate will be maximized, reaching 3.29 m/s, and the pressure loss will be minimized, thus leading to a relatively good scouring performance. With the assurance of both high flow speed and low pressure loss, the nozzle outlet diameter can be set between 30 and 60 mm for optimal flushing effect; at this point, the average mud flow rate is no less than 3 m/s, and the pressure loss is no more than 106 pa, which can help solve the caking problem to some extent. With the increase in length–diameter ratio, the loss of static pressure and total pressure witnessed a relatively high rise, as result of which a smaller long-diameter ratio will be more appropriate, also considering the mud flow rate reaches a maximum value of 3.24 m/s when the ratio is 3 and satisfying results could be achieved when the above ratio has the value of about 3.