logging in or signing up propellers Brainy007 Download Post to : URL : Related Presentations : Share Add to Flag Embed Email Send to Blogs and Networks Add to Channel Uploaded from authorPOINT Insert YouTube videos in PowerPont slides with aS Desktop Copy embed code: (To copy code, click on the text box) Embed: URL: Thumbnail: WordPress Embed Customize Embed The presentation is successfully added In Your Favorites. Views: 4133 Category: Entertainment License: All Rights Reserved Like it (8) Dislike it (0) Added: August 23, 2007 This Presentation is Public Favorites: 1 Presentation Description No description available. Comments Posting comment... By: parvathyr (7 month(s) ago) please give permission for me to download this presentation Saving..... Post Reply Close Saving..... Edit Comment Close By: vishnuneo (7 month(s) ago) hi im a mech student... i hv to present a seminar about marine propellor...so i reqest to u download presentaion on that topic Saving..... Post Reply Close Saving..... Edit Comment Close By: vikasgautam (9 month(s) ago) i am a mechanical 3rd year student.i have an assg.... to presentation about high speed propeller and i have no sufficient meter so i request to u for permition to download the presentation on that topic Saving..... Post Reply Close Saving..... Edit Comment Close By: ankuji (27 month(s) ago) hi i am a student of mechanicl engg... and into my 2nd sem .... we have an assg... to present about any one topic of mechanics ... and i want to give my presentation on propellers .. ur presentation will be of great help ... plzz reply (ankush) coolankush2007@yahoo.co.in Saving..... Post Reply Close Saving..... Edit Comment Close By: lhackel1 (46 month(s) ago) We are working on laser peening technology to reduce the effects of cavitation erosion. Interested? Saving..... Post Reply Close Saving..... Edit Comment Close Premium member Presentation Transcript Slide1: 7.8 PROPELLERS 30 Slide2: HUB ROOT BLADE TIP TIP CIRCLE ROTATION LEADING EDGE TRAILING EDGE PRESSURE FACE SUCTION BACK Screw Propeller PROPELLER DISC 37 Slide3: Some Definitions Pitch -Theoretical distance a propeller would move in one revolution Tip Circle- Circle described by the blade tip rotation Propeller Disc- The area circumscribed by the propeller’s tip circle Leading Edge- Forward edge of the blade, first to encounter the water stream Trailing Edge- Last part of the blade to encounter the water stream Pressure Face- The high pressure side of the propeller blade (the back side as the propeller advances) Suction Back- The low pressure side of the propeller blade (the front side as the propeller advances) Screw Propeller 18 Slide4: Hub pitch diameter The distance that the blade travels in one revolution, P - measured in feet Propeller Pitch 57 Slide5: Propeller Pitch Angle The pitch angle relates the pitch length to the circumference of the propeller blade: tan f = P 2pr … Pitch angle f is the angle that any part of the blade makes perpendicular with the water flow 6 Slide6: Types of Propeller Pitch WITH REGARD TO THE BLADE SHAPE: 1. Constant Pitch- - The pitch angle does not change, it is the same at the root as at the tip of the blade, but the pitch will vary 2. Variable Pitch- The pitch angle changes as the distance from the root changes (f is defined at a blade radius of .7r) 11 tan f = P 2pr Slide7: WITH REGARD TO THE BLADE MOUNTING ON THE HUB: 3. Fixed Pitch- The blade is permanently attached to the hub and cannot change 4. Controllable Pitch- The position of the blade can be altered while the blade rotates, thereby changing the pitch angle Slide8: Left hand screw - Rotates Counter Clock-wise when viewed from astern - Single screw ships use this type Right hand screw - Rotates Clock-wise when viewed from astern Propeller Rotation Counter Rotating Propellers - Have both a right and left hand screw - Eliminates torque created by the rotation - Torque will cause the stern to make a turn in the direction of rotation 22 Slide9: The Skewed Propeller Highly Skewed Propeller for a DDG 51 Advantages: Reduced interaction between propeller and rudder wake - Reduced vibration and noise Disadvantages: Expensive Less efficient operating in reverse 17 Slide10: Propeller Theory The velocity of the water wake at the propeller (VW) is less than the velocity of ship. The difference is called the Speed of Advance The ship drags the surrounding water so that the wake to follow the ship with a wake speed (VW) is generated in the stern. Speed of Advance VA = VS - VW 51 Slide11: Propeller Theory Propeller Efficiency, hP: 20 Slide12: Propeller Theory So for a given thrust, T,: Ao CT Prop Efficiency, hp ...The larger the diameter of propeller, the better the propeller efficiency (~70 % for a well-designed PP.) 60 Slide13: Propeller Cavitation Cavitation occurs on propellers that are heavily loaded, or are experiencing a high thrust loading coefficient The formation and collapse of vapor bubbles on propeller blades where the pressure has fallen below the vapor pressure of water 4 Consequences: 1) Low propeller efficiency (Thrust reduction) 2) Propeller erosion (Mechanical erosion. Severe damage to propeller : up to 180 ton/in²) 3) Vibration due to uneven loading 4) Cavitation noise due to impulsion by the bubble collapse Slide14: 43 Slide15: 56 Slide16: Blade Tip Cavitation Sheet Cavitation Navy Model Propeller 5236 Flow velocities at the tip are fastest so that pressure drop occurs at the tip first. Large and stable region of cavitation covering the suction face of propeller. 47 Slide17: Propeller Cavitation Preventing Cavitation Remove fouling, nicks and scratches Operate at speeds below the cavitation inception speed Increase or decrease the engine RPM smoothly to avoid an abrupt change in thrust. Appropriate pitch setting for controllable pitch propeller For submarines, diving to deeper depths will delay or prevent cavitation as hydrostatic pressure increases 23 Slide18: Propeller Ventilation Ventilation If a propeller operates too close to the water surface, surface air or exhaust gases are drawn into the propeller blade due to the localized low pressure around propeller. The load on the propeller is reduced by the mixing of air or exhaust gases into the water causing effects similar to those for cavitation. Ventilation often occurs in ships in a very light condition(small draft) and in rough seas. 55 Slide19: 27 Slide20: Questions? 21 You do not have the permission to view this presentation. In order to view it, please contact the author of the presentation.
propellers Brainy007 Download Post to : URL : Related Presentations : Share Add to Flag Embed Email Send to Blogs and Networks Add to Channel Uploaded from authorPOINT Insert YouTube videos in PowerPont slides with aS Desktop Copy embed code: (To copy code, click on the text box) Embed: URL: Thumbnail: WordPress Embed Customize Embed The presentation is successfully added In Your Favorites. Views: 4133 Category: Entertainment License: All Rights Reserved Like it (8) Dislike it (0) Added: August 23, 2007 This Presentation is Public Favorites: 1 Presentation Description No description available. Comments Posting comment... By: parvathyr (7 month(s) ago) please give permission for me to download this presentation Saving..... Post Reply Close Saving..... Edit Comment Close By: vishnuneo (7 month(s) ago) hi im a mech student... i hv to present a seminar about marine propellor...so i reqest to u download presentaion on that topic Saving..... Post Reply Close Saving..... Edit Comment Close By: vikasgautam (9 month(s) ago) i am a mechanical 3rd year student.i have an assg.... to presentation about high speed propeller and i have no sufficient meter so i request to u for permition to download the presentation on that topic Saving..... Post Reply Close Saving..... Edit Comment Close By: ankuji (27 month(s) ago) hi i am a student of mechanicl engg... and into my 2nd sem .... we have an assg... to present about any one topic of mechanics ... and i want to give my presentation on propellers .. ur presentation will be of great help ... plzz reply (ankush) coolankush2007@yahoo.co.in Saving..... Post Reply Close Saving..... Edit Comment Close By: lhackel1 (46 month(s) ago) We are working on laser peening technology to reduce the effects of cavitation erosion. Interested? Saving..... Post Reply Close Saving..... Edit Comment Close Premium member Presentation Transcript Slide1: 7.8 PROPELLERS 30 Slide2: HUB ROOT BLADE TIP TIP CIRCLE ROTATION LEADING EDGE TRAILING EDGE PRESSURE FACE SUCTION BACK Screw Propeller PROPELLER DISC 37 Slide3: Some Definitions Pitch -Theoretical distance a propeller would move in one revolution Tip Circle- Circle described by the blade tip rotation Propeller Disc- The area circumscribed by the propeller’s tip circle Leading Edge- Forward edge of the blade, first to encounter the water stream Trailing Edge- Last part of the blade to encounter the water stream Pressure Face- The high pressure side of the propeller blade (the back side as the propeller advances) Suction Back- The low pressure side of the propeller blade (the front side as the propeller advances) Screw Propeller 18 Slide4: Hub pitch diameter The distance that the blade travels in one revolution, P - measured in feet Propeller Pitch 57 Slide5: Propeller Pitch Angle The pitch angle relates the pitch length to the circumference of the propeller blade: tan f = P 2pr … Pitch angle f is the angle that any part of the blade makes perpendicular with the water flow 6 Slide6: Types of Propeller Pitch WITH REGARD TO THE BLADE SHAPE: 1. Constant Pitch- - The pitch angle does not change, it is the same at the root as at the tip of the blade, but the pitch will vary 2. Variable Pitch- The pitch angle changes as the distance from the root changes (f is defined at a blade radius of .7r) 11 tan f = P 2pr Slide7: WITH REGARD TO THE BLADE MOUNTING ON THE HUB: 3. Fixed Pitch- The blade is permanently attached to the hub and cannot change 4. Controllable Pitch- The position of the blade can be altered while the blade rotates, thereby changing the pitch angle Slide8: Left hand screw - Rotates Counter Clock-wise when viewed from astern - Single screw ships use this type Right hand screw - Rotates Clock-wise when viewed from astern Propeller Rotation Counter Rotating Propellers - Have both a right and left hand screw - Eliminates torque created by the rotation - Torque will cause the stern to make a turn in the direction of rotation 22 Slide9: The Skewed Propeller Highly Skewed Propeller for a DDG 51 Advantages: Reduced interaction between propeller and rudder wake - Reduced vibration and noise Disadvantages: Expensive Less efficient operating in reverse 17 Slide10: Propeller Theory The velocity of the water wake at the propeller (VW) is less than the velocity of ship. The difference is called the Speed of Advance The ship drags the surrounding water so that the wake to follow the ship with a wake speed (VW) is generated in the stern. Speed of Advance VA = VS - VW 51 Slide11: Propeller Theory Propeller Efficiency, hP: 20 Slide12: Propeller Theory So for a given thrust, T,: Ao CT Prop Efficiency, hp ...The larger the diameter of propeller, the better the propeller efficiency (~70 % for a well-designed PP.) 60 Slide13: Propeller Cavitation Cavitation occurs on propellers that are heavily loaded, or are experiencing a high thrust loading coefficient The formation and collapse of vapor bubbles on propeller blades where the pressure has fallen below the vapor pressure of water 4 Consequences: 1) Low propeller efficiency (Thrust reduction) 2) Propeller erosion (Mechanical erosion. Severe damage to propeller : up to 180 ton/in²) 3) Vibration due to uneven loading 4) Cavitation noise due to impulsion by the bubble collapse Slide14: 43 Slide15: 56 Slide16: Blade Tip Cavitation Sheet Cavitation Navy Model Propeller 5236 Flow velocities at the tip are fastest so that pressure drop occurs at the tip first. Large and stable region of cavitation covering the suction face of propeller. 47 Slide17: Propeller Cavitation Preventing Cavitation Remove fouling, nicks and scratches Operate at speeds below the cavitation inception speed Increase or decrease the engine RPM smoothly to avoid an abrupt change in thrust. Appropriate pitch setting for controllable pitch propeller For submarines, diving to deeper depths will delay or prevent cavitation as hydrostatic pressure increases 23 Slide18: Propeller Ventilation Ventilation If a propeller operates too close to the water surface, surface air or exhaust gases are drawn into the propeller blade due to the localized low pressure around propeller. The load on the propeller is reduced by the mixing of air or exhaust gases into the water causing effects similar to those for cavitation. Ventilation often occurs in ships in a very light condition(small draft) and in rough seas. 55 Slide19: 27 Slide20: Questions? 21