“…In recent years there has been a growing interest in studying and understanding hydrodynamic flows on curved surfaces, supported by increasing evidence for their relevance in a wide range of problems in nature and engineering. Examples include phenomena in materials science, such as the motion of electrons in graphene (Giordanelli, Mendoza & Herrmann 2018), interface rheology in foams (Cox, Weaire & Glazier 2004) and the dynamics of confined active matter (Keber et al 2014; Janssen, Kaiser & Löwen 2017; Henkes, Marchetti & Sknepnek 2018; Pearce et al 2019); in biophysics, such as flows on curved biomembranes (Arroyo & Desimone 2009; Henle & Levine 2010; Al-Izzi, Sens & Turner 2018; Fonda et al 2018) or fluid deformable surfaces (Torres-Sánchez, Millán & Arroyo 2019; Voigt 2019); in fusion technology, such as plasma motion under toroidal confinement (Boozer 2005); and in geophysics, such as zonal flows on planets and the Sun (Sasaki, Takehiro & Yamada 2015).…”