Nomenclature CF = skin-friction coefficient Is = roll moment of inertia of solid Is = rate of change of 75 k = exit plane radius of gyration for roll L nozzle length m = mass flow rate r = radial distance rc = radius of forced vortex core R nozzle radius at a given section T = torque Va = axial velocity Vt = tangential velocity x = axial coordinate d>/ = initial spin rate of solid o)y = spin rate of solid, cosolid gas = effective spin rate of exhaust gases