CFD Analysis of Herschel-Bulkley Parameter Sensitivity on Pressure Drop in 3D Concrete Printing Nozzle Using OpenFOAM Minsyahril Bukit (a,b*), Mauludi Ariesto Pamungkas (a), Dyonisius J.D.H. Santjojo (a), and Abdurrouf (a)
a. Department of Physics, Faculty of Mathematics and Natural Sciences, Universitas Brawijaya, Malang, Indonesia
*m_bukit[at]student.ub.ac.id
b. Department of Physics, Faculty of Sciences and Engineering, Universitas Nusa Cendana, Kupang, Indonesia
Abstract
The extrusion of fresh mortar through a converging nozzle in 3D concrete printing (3DCP) involves complex non-Newtonian flow governed by three Herschel-Bulkley (HB) parameters: yield stress (tau0), consistency index (K), and flow behavior index (n). Although these parameters are routinely used in 3DCP simulation, their relative contributions to nozzle pressure drop have not been systematically quantified under varying geometric and flow conditions. This study presents a one-at-a-time (OAT) CFD sensitivity analysis using OpenFOAM 9 and simpleFoam solver, isolating the individual effects of HB parameters on pressure drop across a range of contraction ratios (CR = 2.0-4.5), inlet velocities (0.2-1.2 m/s), and taper angles (15-30 degrees). Simulations were performed on a grid-independent axisymmetric mesh of 3,420 cells (GCI = 2.3%), validated against the exact analytical HB pipe-flow solution. Results confirm that the flow behavior index n is the dominant rheological parameter, producing a 108% variation in pressure drop over n = 0.35-0.55 -- 13x larger than the effect of yield stress tau0 (~8%). The consistency index K ranks second at 54% variation. Geometrically, contraction ratio CR dominates with 475% variation (CR = 2.0-4.5), far exceeding all rheological parameters. This counter-intuitive hierarchy -- where tau0, the conventional 3DCP printability metric, has the weakest influence on extrusion pressure -- provides practical guidance for mortar formulation and nozzle design, suggesting that flow index and contraction ratio are the primary design variables for pressure management in 3DCP systems.
