Understanding Crashback in Marine Propellers Using an Unsteady Actuator Disk Model

Abstract

An unsteady actuator disk model is constructed in order to understand unsteadiness in crashback operation of a marine propeller as a competition between two flows of opposite direction: reversed flow through the propeller and the ambient flow due to motion of the vessel. The large eddy simulation methodology is applied to predict the flow corresponding to forward and crashback modes of operation using a non-dissipative, robust numerical algorithm developed by Mahesh et al. (2004, J. Comput. Phys., 197: 215-240) for unstructured grids. Flow visualization shows creation and shedding of unsteady ring vortices which are correlated to the fluctuation of the thrust coefficient. Results of the model are compared to the LES of the full propeller geometry as well as to experimental data.

Large eddy simulation of flow around a reverse rotating propeller

“…The cycle appears to restart with the stable case at t = 2.8 s. No regular shedding or cycle frequency has been observed due to the extreme sensitivity of the flow to small perturbations (Bernero 2000). A similar flow has been computationally studied using an unsteady actuator disk model by Vyšohlid & Mahesh (2007). A schematic of the actuator disk model is shown in figure 12(a); note that the actuator disk enforces constant flow velocity U P against the free-stream velocity U.…”

“…A schematic of the actuator disk model is shown in figure 12(a); note that the actuator disk enforces constant flow velocity U P against the free-stream velocity U. Vyšohlid & Mahesh (2007) performed simulations at U P /U = −1.0 and noted regular vortex ring shedding. Figure 12(b-e) from Vyšohlid & Mahesh (2007) shows the evolution of the vortex ring in time.…”

“…Vyšohlid & Mahesh (2007) performed simulations at U P /U = −1.0 and noted regular vortex ring shedding. Figure 12(b-e) from Vyšohlid & Mahesh (2007) shows the evolution of the vortex ring in time. A new vortex ring is created around the actuator disk (b), advected with the free stream (c), stretched (d), and shed (e).…”

“…Chang et al (2008) also used LES to predict shear and bending stresses on the blade surface, and good agreement was observed. LES was performed for a simple actuator disk model of crashback by Vyšohlid & Mahesh (2007). Verma, Jang & Mahesh (2012) investigated the effect of an upstream submarine hull on a propeller in crashback using the same computational methodology.…”

“…online) (a) Schematic of the actuator disk model, (b-e) time evolution of vortex ring in the actuator disk model at U P /U = −1.0(Vyšohlid & Mahesh 2007). (Colour online) Time-averaged flow field at x/R = 0 and J = −0.7: (a) axial velocity, (b) pressure.…”