Propeller

About: Propeller is a research topic. Over the lifetime, 21284 publications have been published within this topic receiving 113996 citations.

On the Vortex Theory of Screw Propellers

Abstract: The vortex-theory of screw propellers develops along similar lines to aerofoil theory. There is circulation of flow round each blade; this circulation vanishes at the tip and the root. The blade may be replaced by a bound vortex system, which, for the sake of simplicity, may be taken, as a first approximation, to be a bound vortex line. The strength of the vortex at any point is equal to Γ, the circulation round the corresponding blade section. From every point of this bound vortex spring free, trailing vortices, whose strength per unit length is —∂Γ/∂ r , where r is distance from the axis of the screw. When the interference flow of this vortex system is small compared with the velocity of the blades, the trailing vortices are approximately helices, and together build a helical or screw surface. Part of the work supplied by the motor is lost in producing the trailing vortex system. When the distribution of Γ along the blade is such that, for a given thrust, the energy so lost per unit time is a minimum, then the flow far behind the screw is the same as if the screw surface formed by the trailing vortices was rigid, and moved backwards in the direction of its axis with a constant velocity, the flow being that of classical hydro dynamics in an inviscid fluid, continuous, irrotational, and without circulation. The circulation round any blade section is then equal to the discontinuity in the velocity potential at the corresponding point of the screw surface. Further, for symmetrical screws, the interference flow at the blade is half that at the corresponding point of the screw surface far behind the propeller. An approximate solution for the irrotational motion of a screw surface in an inviscid fluid was given by Prandtl. The accuracy of the approximation increases with the number of blades and with the ratio of the tip speed to the velocity of advance, but for given values of these numbers we have no means of estimating the error, since the exact solution of the problem has not yet been found. It is the main object of this work to find the exact solution.

Practical Ship Hydrodynamics

Abstract: Introduction Overview of problems and approaches Model test and similarity laws Full scale tests Numerical approaches (Computational Fluid Dynamics) Basic equations, Basic techniques Applications. Propeller Flows: Propeller geometry and other basics, Propeller curves Numerical methods for propeller design Lifting line theory Lifting surface theory BEM for propellers Field methods Cavitation Experimental approach Propeller design procedure. Resistance and propulsion: Resistance and propulsion concepts Interaction between ship and propeller Decomposition of resistance Experimental approach Towing tanks and experimental set up Resistance test Method ITTC 1957 Method of Hughes-Prohaska Propulsion test Additional resistance under service conditions Simple design approaches CFD approaches for steady flow Wave resistance computations Viscous flow computations Problems for fast and unconventional ships. Ship Seakeeping: Introduction to seakeeping Experimental approaches (model and full-scale) Waves and seaway Airy waves (harmonic waves of small amplitude) Natural seaway Wind and seaway Wave climate Numerical prediction of ship seakeeping Overview of computational methods Strip method Rankine panel methods Problems for fast and unconventional ships Further quantities in regular waves Ship responses in stationary seaway Simulation methods Long-term distributions Slamming. Manoeuvring: Simulation of manoeuvring with known coefficients Coordinate systems and definitions Body forces and manoeuvring motions Linear motion equations CFD for manoeuvring Experimental approaches Manoeuvring tests for full-scale ships in sea trials Model tests Rudders Computation of body forces Slender-body theory Influence of heel Shallow-water effect Jet thrusters Stop manoeuvres. Boundary element methods: Green function formulation Integral equations Source elements Point source Regular first-order panel Jensen panel Higher-order panel Vortex elements Dipole elements Point dipole. Numerical examples for BEM: Two-dimensional body in infinite flow Theory Numerical implementation.

Radiated noise characteristics of a modern cargo ship

Abstract: Extensive measurements were made of the radiated noise of M/V OVERSEAS HARRIETTE, a bulk cargo ship (length 173 m, displacement 25 515 tons) powered by a direct-drive low-speed diesel engine—a design representative of many modern merchant ships. The radiated noise data show high-level tonal frequencies from the ship’s service diesel generator, main engine firing rate, and blade rate harmonics due to propeller cavitation. Radiated noise directionality measurements indicate that the radiation is generally dipole in form at lower frequencies, as expected. There are some departures from this pattern that may indicate hull interactions. Blade rate source level (174 dB re 1 μPa/m at 9 Hz, 16 knots) agrees reasonably well with a model of fundamental blade rate radiation previously reported by Gray and Greeley, but agreement for blade rate harmonics is not as good. Noise from merchant ships elevates the natural ambient by 20–30 dB in many areas; the effects of this noise on the biological environment have not been widely investigated.

Propeller Performance Data at Low Reynolds Numbers

Abstract: While much research has been carried out on propellers for full-scale aircraft, not much data exists on propellers applicable to the ever growing number of UAVs. Many of these UAVs use propellers that must operate in the low Reynolds number range of 50,000 to 100,000 based on the propeller chord at the 75% propeller-blade station. Tests were performed at the University of Illinois at Urbana-Champaign (UIUC) to quantify the propeller efficiency at these conditions. In total, 79 propellers were tested and the majority fit in the 9- to 11-in diameter range. During the tests, the propeller speed (RPM) was fixed while changing the wind-tunnel speed to sweep over a range of advance ratios until reaching the windmill state (zero thrust). To examine Reynolds number effects, typically four RPM’s were tested in the range 1,500 to 7,500 RPM depending on the propeller diameter. Propeller efficiencies varied greatly from a peak near 0.65 (for an efficient pr opeller) to near 0.28 (for an exceptionally poor propeller). Thus, these results indicate that proper propeller selection for UAVs can have a dramatic effect on aircraft performance.

Mechanisms of evolution of the propeller wake in the transition and far fields

Abstract: In the present study the mechanisms of evolution of propeller tip and hub vortices in the transitional region and the far field are investigated experimentally. The experiments involved detailed time-resolved visualizations and velocimetry measurements and were aimed at examining the effect of the spiral-to-spiral distance on the mechanisms of wake evolution and instability transition. In this regard, three propellers having the same blade geometry but different number of blades were considered. The study outlined dependence of the wake instability on the spiral-to-spiral distance and, in particular, a streamwise displacement of the transition region at the increasing inter-spiral distance. Furthermore, a multi-step grouping mechanism among tip vortices was highlighted and discussed. It is shown that such a phenomenon is driven by the mutual inductance between adjacent spirals whose characteristics change by changing the number of blades.