# Counter-Rotating Open Rotors performance evaluation¶

## Input Parameters¶

The following keys can be set:

• base – (type = antares.Base ) – The base must contain:
• rho_inf – (type = float ) – infinite density

• v_inf – (type = float ) – infinite velocity

• duplication – (default = True, type = boolean ) – duplication (rotation) of the forces. If not, for each row, the coefficients represent the forces, acting on a single blade, multiplied by the number of blades

## Main functions¶

class antares.treatment.turbomachine.TreatmentCRORPerfo.TreatmentCRORPerfo
execute()

Compute the similarity coefficients (forces) for a CROR. It is assumed that the forces come from a single canal computation (periodic or chorochronic when using HB/TSM approach). The forces are then duplicated by the number of blades.

Four coefficients are computed: the traction defined as

$$\displaystyle C_t = |\frac{flux\_rou}{rho\_inf \cdot n^2 \cdot D^4}|$$,

the power coefficient defined as

$$\displaystyle C_p = |\frac{2 \pi \cdot torque\_rou}{rho\_inf \cdot n^2 \cdot D^5}|$$ (note the simplification of the rotation frequency on the expression of the power coefficient),

the propulsive efficiency computed from the traction and the power coefficients

$$\displaystyle \eta = J \frac{C_t}{C_p}$$, where $$J$$ is the advance ratio defined as $$\displaystyle J = |\frac{v\_inf}{n \cdot D}|$$ (note that this widely used formulation for propeller might be reconsidered in presence of a second propeller. Indeed, the second rotor “doesn’t see” the speed $$v\_inf$$),

and the figure of merit

$$\displaystyle FM = \sqrt{\frac{2}{\pi}}\frac{C_t^{3/2}}{C_p}$$

These formulae are computed rotor per rotor. The global performance is evaluated as follow:

$$\displaystyle C_t^{global} = C_t^{front} + C_t^{rear}$$,

$$\displaystyle C_p^{global} = C_p^{front} + C_p^{rear}$$,

$$\displaystyle \eta^{global} = \frac{J^{front} \cdot C_t^{front} + J^{rear} \cdot C_t^{rear}}{C_p^{global}}$$

$$\displaystyle FM^{global} = \sqrt{\frac{2}{\pi}}\frac{(C_t^{global})^{3/2}}{C_p^{global}}$$

Returns

the input base with the forces, a new zone ‘global’, and as many instants as the input base has. If the input base comes from a HB/TSM computation, the mean, and the harmonics are also computed. Note that the amplitude of the harmonics are given divided by the mean value.