CFD Numerical Simulation and Experimental Study of Effects of Screw-Sleeve Fitting Clearance upon Triangular Thread Labyrinth Screw Pump (LSP) Performance

How fitting clearance between screw and sleeve of labyrinth screw pump(LSP) effects the pump performance and what law it follows are still unsolved problems for LSP design. So the fluid quasi-steady flow in triangular thread LSP with different clearances is approximately modelled by the shear-stress transport k-ω model (SST k-ω model) in multiple reference frame (MRF) of CFD, and the pump characteristics experiments are also carried out. In analysis, fluid flow is simplified as a linear superposition of Couette flow dragged by rotor screw and pressure flow driven by differential pressure of LSP. The CFD simulated results reveal that the clearance has scarcely effect on drag flow, but the average axial pressure flow velocity is the maximal in clearance and it increases with increase of clearance at the same differential pressure; Leakage mainly occurring between the lands of screw and sleeve can well be estimated by leakage formula for a narrow slot with coefficient ζ of 1.62. The CFD simulated lift-capacity curve of triangular thread LSP becomes more flat with clearance increase, which is confirmed by the pump performance experiments. The experimental results also indicate that with increase of clearance, the pump efficiency obviously decreases especially at the vicinity of the highest efficiency point while the power decreases a little in a whole range of capacity. Finally, the paper presented a set of simple and tidy conversion expressions to predict the capacity, head and efficiency changing with clearance for triangular thread LSP, which has made some applications in engineering.