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Shaft Engines
Published in Ahmed F. El-Sayed, Aircraft Propulsion and Gas Turbine Engines, 2017
Section 6.2.2 discusses aero piston engines and Section 6.2.3 deals with propellers. Propellers installed in combination with piston engines are very similar to those fitted to turboprop engines. Propellers are classified based on their source of power, material, coupling to the output shaft, control, number of propellers coupled to each engine, direction of rotation, propulsion method, and the number of blades. Detailed aerodynamic theories are discussed regarding propeller design, covering axial momentum (or actuator disk), modified momentum, and the blade element. Nondimensional parameters are derived defining propeller performance; namely, thrust and power coefficients, as well as the advance ratio. Detailed analysis of the thrust generated by each blade segment and the total thrust are described through worked examples. Charts are given for the thrust, power, and propulsive efficiency of two- and three-bladed propellers.
Numerical investigation of hydrodynamic and hydro-acoustic performance of underwater propeller operating in off-design flow conditions
Published in Journal of Marine Engineering & Technology, 2020
Muhammad Rehan Naseer, Emad Uddin, Aamir Mubashar, Muhmmad Sajid, Zaib Ali, Khalid Akhtar
For this purpose, the FW-H method is implemented on the values obtained from hydrodynamic analysis. Figure 11 depicts the comparison of acoustic pressure, for three different values of advance ratios, in the cases where the incoming flow is straight (linear sailing) and Figure 12 shows the comparison, for the cases of off-design flow conditions (oblique flow). Two observations are noted as the flow conditions change from the straight flow to oblique flow. The acoustic pressure curves become irregular for the oblique flow as compared to the straight flow. Secondly, pressure magnitude increases significantly from 60 psi for the straight flow to 500 psi for the oblique flow of 20 degrees at J = 0.7. The third interesting observation is related to the decrease in frequency of the acoustic pressure for the oblique flow condition, this is further explained later. As a result of the provision of angle to the incident flow, the formation of secondary vortices at the leading edges of the propeller for the oblique flow changes the noise behaviour from regular sinusoidal to irregular. While considering the hydrodynamic functioning aspect of the propeller, the origination of secondary vortices also induces the cavitation process due to the presence of adverse pressure gradient at the site. From Figures 11 and 12, it is also elucidated that there is an upsurge in the magnitude of the acoustic pressure, when the advance ratio tends to reduce and the reason to this enhancement can possibly be explained as the vortex shedding in the wake of the propeller.