Transient lift force on a blade during cutting of a vortex with non-zero axial flow

Abstract

The problem of orthogonal penetration of a blade into the core of a vortex with non-zero axial flow was studied using a combination of scaling theory, a heuristic plug-flow model and full Navier-Stokes simulations. The particular focus of this paper was to understand the mechanics of the transient lift force that occurs during the initial penetration of the blade leading edge into the vortex core, and the relationship of this transient force to the steady-state lift force that develops due to the difference in vortex core radius over the blade surface. The three modelling approaches all lead to the conclusion that the maximum value of the lift coefficient for the transient blade penetration force is proportional to the impact parameter and inversely proportional to the axial flow parameter. This observation is used to develop a simple expression that collapses the predictions of the full Navier-Stokes simulations for lift coefficient over a wide range of parameter values.

Underlying mechanisms of propeller wake interaction with a wing

“…An effective and useful insight is given by the simplified models of a vortex–body orthogonal and streamwise interference, which, to some extent, resemble the type of interaction of the propeller blade and hub vortices with a wing, respectively. These simplified vortex–body interactions have received much attention in the literature, in particular for the study of the structural, aeroacoustic, manoeuvring and control effects related to the interaction of helicopter rotor blades with concentrated tip vortices (see, e.g., Brentner & Farassat 1993; Filippone & Afgan 2008; Glegg & Devenport 2017; Saunders & Marshall 2017), and have been addressed by a number of empirical and theoretical studies for different vortex orientations and positions with respect to the wing (see, e.g., Rockwell 1998).…”

The wake structure of a propeller operating upstream of a hydrofoil

“…The presence of an axial velocity within the vortex core is the source of the asymmetries observed on the suction and pressure sides, producing a lift force, in agreement with results from earlier inviscid computations. Recent computations by Saunders & Marshall (2015, 2017), in a similar configuration, identified three phases of the vortex cutting process: (i) vorticity is generated at the leading edge of the blade, due to the velocity induced by the approaching vortex; such vorticity is oriented in the opposite direction, compared to that within the vortex core; (ii) vorticity diffusion and destruction occur between the vortex core and the boundary layer on the leading edge of the blade, due to the opposite orientation of vorticities; (iii) the process of vorticity destruction within the vortex core stops, due to reorientation of the leading edge vorticity within the boundary layer; as a consequence the primary vortex keeps wrapping around the leading edge, stretching while moving downstream across the blade.…”

Vortex Model and Blade Span Influence on Orthogonal Blade-Vortex Interaction Noise

“…In the past, OBVI has been studied thoroughly within the helicopter field with a focus on main rotor/tail rotor interactions [2]. Analyses were carried out by means of dedicated experiments [3][4][5][6][7][8][9][10], analytical modeling [11,12] and numerical computations [7,[13][14][15][16][17][18][19]. These studies came to the conclusion that OBVI is complex and exhibit various regimes depending on several non-dimensional parameters such as: the ratio of the vortex advection speed and vortex maximum tangential velocity, the ratio of the blade thickness and vortex core radius, the ratio of the vortex axial velocity deficit or excess and vortex maximum tangential velocity.…”