Development of correctors on design of optimum contra-rotating propellers under slipstream contraction condition

Name: Nattanun Subsamart

Organization : Chulalongkorn University. Mechanical Engineering Department

Name: Chirdpun Vitooraporn

Organization : Chulalongkorn University. Mechanical Engineering Department

Email : chirdpun@hotmail.com

keyword: Contra-rotating propellers

; Lifting line

; Slipstream contraction

; Inflow velocity

Abstract: This research extends our previous works on the design of optimum contra-rotating propellers (CRPs) by investigating correctors that play an important role on rectifying the discrepancy of design results obtained from calculation and CFD. From our previous works, the lifting line theory with slipstream contraction condition along with the calculus of variation method are used to find the optimum CRPs that provide the required thrust with minimum power under axial uniform flow. These optimum CRPs are then simulated by using the CFD program in order to verify the calculation results. Some differences in thrusts and torques obtained from calculation and CFD on each optimum CRP are found. The cause of these differences are then investigated. It is appeared that the inflow velocity on each propeller is differ from the assumption used in calculation in which inflow velocity appearing on propeller equals to initial inflow velocity that entering through CRPs. This is because the position in defining the inflow velocity that entering through CRPs and the wake flow between fore and aft propellers in CFD make the inflow velocities appearing on propellers differ from those in calculation. Correctors are then used to multiply with the initial inflow velocity to represent new values of inflow velocities appearing on propellers. Through the same calculation process, new optimum CRPs using these correctors are obtained and simulated by CFD program. Trials of different corrector values at different conditions are done to find proper corrector values that conform results from both calculation and CFD. Through the use of these correctors, it is found that the inflow velocity appearing on propeller not only changes differently in each condition but also between fore and aft propellers. To find the variation of correctors along with the inflow velocity, parameters on each condition that affect the value of inflow velocity are investigated in this study. It is found that the inflow velocity is directly proportional to advance ratio and inversely proportional to thrust coefficient. This is because at low advance ratio and high thrust coefficient, the propeller has high rotational speed and strong circulation which tend to create stronger flow field turbulence. This causes the reduction of inflow velocity on propeller. Moreover, the inflow velocity on aft propeller is always less than that on fore propeller, as aft propeller has to encounter with wake flow behind the fore propeller while fore propeller approaches to more uniform flow. Under these findings, correctors can then be concluded as function of these parameters and hence can be calculated to find proper values of corrector to multiply with the inflow velocity.

King Mongkut's University of Technology North Bangkok. Central Library

Address: BANGKOK

Email: library@kmutnb.ac.th

Created: 2020

Modified: 2021-04-29

Issued: 2021-04-29

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BibliograpyCitation : ใน มหาวิทยาลัยมหิดล คณะวิศวกรรมศาสตร์ ร่วมกับ สมาคมวิศวกรเครื่องกลไทย. การประชุมวิชาการเครือข่ายวิศวกรรมเครื่องกลแห่งประเทศไทย ครั้งที่ 34 (ME-NETT 2020) (pp.96-105). นครปฐม : มหาวิทยาลัยมหิดล

eng

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