Experimental and Numerical Analysis of a Propeller Downstream Flow at Static Conditions and Determination of Semi-Empirical Equations

In the current paper, downstream flow field of a propeller at low Reynolds numbers and at static conditions (zero flight speed) is investigated experimentally. This propeller can be utilized in UAVs. Propeller diameter is 56 centimeter and it is investigated at 2550 to 5670 rpm experimentally. Experiment results show that propeller rpm increasing, increases induction velocity. Flow swirl ratio and axial flow coefficient decrease along propeller radius at different propeller rpm. Experimental results of absolute velocity of swirl flow at the propeller airfoil trailing edge downstream is fairly similar to the free vortex flow theory at static condition along the blade radius.  At static condition for r/R<0.8, semi-empirical equations are suggested for variation of flow swirl ratio and axial flow coefficient at downstream of propeller. The propeller is also simulated with numerical simulations. Relative standard deviation of numerical and experimental results for propeller thrust and power are 0.4 and 4.1, respectively. The exponential coefficient (n) which predicts numerical axial flow downstream of propeller for r/R<0.8 has a 7.7 relative standard deviation with experimental results at static condition.