COMPONENT of jet speed. Single-stage impulse turbine is known as de Laval turbine. For single-stage impulse turbine the OPTIMUM flow ratio, \(ρ = \frac{u}{V} = \frac{{cos\alpha }}{2}\)Parson's turbine is a single-stage REACTION turbine. For reaction turbine For single-stage impulse turbine the optimum flow ratio, \(ρ = \frac{u}{v} = \cos\alpha\)Therefore the optimum VALUE of ρ for de Laval turbine will be 1/2 and for Parson's turbine, it will be 1.