《船舶原理》第2章Geometry of Marine Propellers.pptx

Section 2Geometry of Marine Propellers5-bladed propellerGeneral terms of blade geometryNumber of blades, Z -bladed propellerHub/boss: part connecting blades & the shaftBoss cap: streamlined conical bodyDirection of rotation: left- & right- handedBlade tip & rootLeading-edge & trailing-edge: L.E. & T.E. (will change with rotating direction)Face & back, pressure & suction sideBoss capBoss/HubTipRootSection 2Geometry of Marine PropellersGeneral terms of blade geometryNumber of blades, Z -bladed propellerHub/boss: part connecting blades & the shaftBoss cap: streamlined conical bodyDirection of rotation: left- & right- handedBlade tip & rootLeading-edge & trailing-edge: L.E. & T.E. (will change with rotating direction)Face & back, pressure & suction sideBoss capBoss/HubBackFaceL.E.L.E.T.E.T.E.Tip circle: trace of rotating blade tip when the propeller does not advanceD: propeller diameter, diameter of tip circleA0: disk area of propeller, A0=?D2/4Twin propellers: inward- & outward-turningTip clearance: shortest distance betweentip & stern hullHelicoidal surface & helixA helicoidal surface is a surface swept out by a straight line AB, which advances along axis OO1 at a uniform speed, and meanwhile rotates aroundOO1 with a uniform angular speed.AB is called the generating line.A helix is the trajectory of a point on AB, or the intersection of the helicoidal surface and a cylindrical surface coaxial with OO1.When AB makes a complete revolution to reach its final position A1B1, the distance AA1 or BB1 is called the pitch, denoted by P.When the coaxial cylindrical surface is expanded on a flat surface, the helix will become the straight line BB1, which makes an angle with the horizontal line BC at an angle ? called the pitch angle and determined bytan? = P/ (2?r )B1Definition of Pitch AngleP?B 2?rCPropeller blade section & pitchThe blade section at radius r is defined as the section formed by cutting the blade with a coaxial cylindrical surface of r