Subsonic Propellers Research Articles

Wall Blockage Correction for Shrouded Wind Turbines and Propellers

Three methods are provided for calculating wind-tunnel (or finite computational fluid dynamics domain) induced wall blockage corrections for shrouded wind turbines and subsonic propellers. To this end, it is first shown that all open-rotor and shrouded wind turbines and propellers can be represented analytically as members of a single general family. Thereafter, power harvesting and thrusting predictions for both wind turbines and propellers, respectively, are reduced to solutions of pairs of polynomial equations, for which exact numerical solutions are provided. Additionally, easily applied, semiempirical, and closed-form perturbation solutions are provided. For wind turbines, it is shown that even small blockage levels can induce appreciable correction factors, whereas for propellers, blockage corrections were found to be negligibly small for all practical blockage levels.

Subsonic propellers in a strong wind as anomalous X-ray pulsars

The appearance of subsonic propellers situated in a strong wind is discussed. We show that it is similar to the appearance of anomalous X-ray pulsars (AXPs) provided the mass and the magnetic moment of neutron stars are 1.4 solar masses, and 2E+30 G cm^3, respectively, and the strength of the wind is M_c = 3E+17 g/s. Under these conditions, the spin periods of subsonic propellers are limited within the range of 5-15 s, and the expected spin-down rates are close to 7E-11 s/s. The mass accretion rate onto the stellar surface is limited to the rate of plasma penetration into its magnetosphere at the boundary. As this process is governed by the reconnection of the field lines, the accretion rate onto the stellar surface constitutes 1-2% of M_c. In this case the X-ray luminosity of the objects under consideration can be evaluated as 4E+35 erg/s. The model predicts the existence of at least two spatially separated sources of the X-ray emission: hot spots at the stellar surface, and the hot atmosphere surrounding the magnetosphere of the star. The ages of the subsonic propellers under the conditions of interest are limited to 10^5 yr.

Influence of Shaft Angle of Attack on Sound Radiation by Subsonic Propellers

The formulation to account for effects of propeller angle of attack on acoustic radiation by propellers is presented. A propeller operating at an angle of attack presents a nonuniform ine ow situation that is known to have a pronounced ine uence on noise. Noise predictions, based on this new formulation, are compared with measured wind-tunnel data. Predictions for observers e xed in the propeller plane are also included to assess the ine uence of shaft angle of attack. Nomenclature c0 = ambient speed of sound f = function dee ning blade surface l = local force per unit area of blade acting on e uid lr = component of loading vector in direction of radiation vector, liri M = source Mach number Mr = component of source Mach vector in direction of

Prévision du bruit de raie émis par un rotor : application à l'aéronautique

Prediction of rotor tone noise is a major issue both in industry andin aeronautics for reducing sound radiation. Two frequency methods are described, the first applies to open rotors and the second solves the wave equation inside a cylindrical duct. It is shown that the main terms are the same in both cases. This is particularly useful for studying supersonic fans of turbofans because computations of isolated propellers are then valid. Emphasis is put on the differences with the directivities radiated by conventional subsonic propellers