Numerical Investigations of Ducted Fan Hover Performance for FIW Applications

Abstract

In the present study, the ducted fan hover performance is numerically investigated for Fan-In-Wing (FIW) applications using a high-fidelity unstructured grid Computational Fluid Dynamics (CFD) solver U 2 NCLE. Effects of the ducted fan geometric parameters such as the fan blade twist and the duct inlet lip radius are evaluated in details for the ducted fan hover efficiency and stall margin over a wide range of collective angles. Both open fans and ducted fans are investigated for their aerodynamic characteristics including the blade sectional loadings and the duct pressure distributions. The induced inflow velocity and the downwash wake profiles of the ducted fan systems are investigated under different fan blade twists, and the flow separation phenomena on the blade and duct surfaces are evaluated with different duct inlet profiles. Computational results indicate that the blade twist provides consistent effects on the Figure of Merit and the stall margin in both the open and ducted fans being studied, and the duct inlet profile has a significant impact on the overall hover performance of the ducted fan system. The numerical studies performed here provide better understanding of the aerodynamic interactions inside the ducted fans, and insight into the optimal aerodynamics design for the future FIW systems. Nomenclaturenumber of blades OF = open fan p = pressure P = fan power PL = power loading, / 1 Associate Professor, 2 Q = fan torque R = fan blade radius R lip = duct inlet lip radius RBF = radial basis function s/D = duct distance T = thrust y + = y plus value TPP = blade tip path plane V tip = blade tip velocity, Ω V z = induced velocity, axial velocity, downwash velocity ρ = density σ = blade solidity, / θ 75 = fan blade collective angle at 75% span φ = inflow angle Ω = fan rotational speed

Numerical Investigation of Effect of Parameters on Hovering Efficiency of an Annular Lift Fan Aircraft

“…Table 2 shows, when the radius of curvature of inlet lip R lip increased from 2.5% to 4.7%, the figure of merit increased from 0.665 to 0.704. This result is consistent to other's observation that larger inlet lip radius promotes hover performance [7,24]. However, R lip is constrained by the depth of duct because the duct cannot be very thick in order to reduce the aerodynamic drag in cruise flight.…”

Review on ducted fans for compound rotorcraft

“…Though good agreement with the experimental data was achieved, very limited data was presented. Sheng et al (55) simulated a 24-inch diameter, six-bladed ducted fan in hover (Fig. 9(f)), representing a simplified fan-in-wing configuration.…”

“…(37) (c) Akturk and Camci. (34) (d) Ye et al (54) (e) Xu et al (27) (f) Sheng et al (55) (g) Jimenez and Singh. (56) (h) Biava and Barakos.…”

“…Sheng et al (55) simulated a 24-inch diameter, six-bladed ducted fan in hover (Fig. 9(f)), representing a simplified fan-in-wing configuration.…”

“…As mentioned earlier, the separation depends on the difference between the fan power and the free-stream speed, the cross-wind angle, and the inlet lip geometry. In fact, several studies (17,55) on fan-in-wing types reported lip separation in hover conditions. It is argued that there could be a critical lip radius of 6% duct diameter, below which separation would take place.…”