A Study Of Hydrodynamic Optimization Approach Of Submarine Propulsors Based On Panel Method

The propulsor is a main source of submarine vibration and noise radiation,and its hydrodynamic performance is closely related to the combat capability of a submarine.The design of a submarine propulsor is a complicated process which involves many geometric parameters and design targets.In this dissertation,a study of the hydrodynamic optimization approach for submarine propulsors is conducted based on the panel method and optimization algorithms.The study of the whole dissertation includes the design of two-dimensional(2-D)blade sections,numerical prediction of effective wake field and tonal noise of propellers,optimization of seven-bladed propellers as well as the rotor of a pump-jet propulsor in effective wake fields.The main contents and conclusions of the dissertation are summarized as follow.(1)A design approach for 2-D blade sections is proposed based on the Newton-Raphson method and specified lift distribution.The 2-D design includes camber line design and blade section design.A design concept based on lift distribution and a parameterized lift distribution curve is proposed for the 2-D design.The Newton-Raphson iteration is capable of designing camber lines and sections with specified lift distributions quickly.The SJ series camber lines are developed in the camber line design as a reference for propeller design.In the section design,the thickness distribution is parameterized by the PARSEC polynomial.Flow simulations of the designed sections indicate that the cavitation buckets can be adjusted by changing the lift distribution.The parametric expression of blade section geometry as well as the SJ camber lines are utilized in the optimization design of propellers.(2)The effective wake field of the SUBOFF submarine is numerically predicted by a hybrid approach coupling panel method and RANS simulation.The hull resistance and wake field are predicted by RANS simulation,while the propeller performance is estimated by panel method.The action of a propeller in RANS simulation is replaced by a body force model.The body force zone is an axisymmetric volume formed by rotating the propeller profile around its shaft axis.The mapping of force fields from potential flow to body force zone in RANS simulation is executed by proposed radial basis function(RBF)interpolation on equivalent planes.The accuracy of the RBF interpolation scheme is very high,while the procedure is simple and fast.The effective wake field,an input for propeller optimization design,is determined at self-propulsion point by several iterations.The unsteady pressure distributions of a seven-bladed propeller in effective wake field are treated as inputs for the prediction of propeller tonal noise by using Farassat 1A formula.Firstly,tonal noises of the propeller in nominal and effective wake fields are compared.Then the effects of skew and rake distributions to tonal noise are analyzed.The results show that the maximum sound pressure level(SPL)at blade frequency in effective wake is 3 dB lower than that in nominal wake at same observation positions.And larger skew is positive to decease the SPL and acoustic energy at blade frequency in effective wake for a seven-bladed propeller.(3)The hydrodynamic optimization of a seven-bladed propeller in open water is conducted based on panel method and multi-objective optimization algorithm.The chord length distribution is parameterized by a proposed polynomial,and pitch,camber,skew distributions are all parameterized by B splines.The thickness distribution and camber line of a blade section are respectively parameterized by PARSEC polynomial and SJ series camber lines.A correlation analysis based on design of experiments is conducted to reduce the design variables and determine their design space.Then multi-objective optimizations aiming at improving open water efficiency and reducing the pressure peak near blade tip are carried out by the Non-dominant Sorting Differential Evolution Algorithm(NSEA).The hydrodynamic performances of the optimized propellers are also evaluated by RANS simulation,which shows that the design strategy can improve the propeller efficiency and reduce pressure peak at blade tip.The propeller optimization in open water determines the parameterization strategy and optimization work flow for propellers in this dissertation.(4)The seven-bladed propeller is further optimized in effective wake field.The parameterization approaches of propeller geometric distributions are the same as those in open water optimization.A multi-objective optimization for the whole propeller is carried out to improve the efficiency and bearing force and yields an optimal propeller named GO18.Then the local geometry near the tip of propeller GO18 is further optimized to reduce the acoustic energy level of the propeller.A local optimized propeller named LO343 is obtained.The two optimized propellers have lower expanded area ratio,larger pitch,camber(0.55R~0.95R)and skew than those of the original propeller.At last,hydrodynamic performances of the original propeller and the propeller LO343 are compared by model tests in the cavitation tunnel of Shanghai Jiao Tong University.The model tests show that the efficiency of LO343 is 1.3% higher than that of the original propeller.The inception lines of back and tip vortex cavitation of LO343 are about 25% lower than those of the original propeller.The SPL of cavitating propeller LO343 is 3 dB higher than that of the original propeller in a 1/3 octave bandwidth centered at 1260 Hz.The non-cavitating SPLs of the two propellers at low frequencies are close to each other,but the original propeller generates singing sounds,which doesn’t occur on the propeller LO343.The optimized propeller performs better than the original propeller in efficiency,back and tip vortex cavitation inception and radiated noise.(5)A preliminary study of the optimization design for the rotor of a pumpjet propulsor(PJP)fitted to the SUBOFF submarine is conducted via the presented approach.The effective wake field is numerically predicted by the hybrid approach,and then the rotor is optimized in the effective wake field.The stators and duct of the PJP are treated as appendages of the hull and evaluated by RASN simulation,while the rotor of the RPJ is estimated by unsteady panel method.The force field interpolation between panel method and RANS grid is executed by RBF interpolation on equivalent planes.The effective wake field at rotor plane is predicted at submarine self-propulsion point through several iterations.The comparison between wake fields shows that wakes sheding from the pre-swirl stators are captured in the effective wake field.The differences between effective and nominal wake fields are very clear.The parameterization methods of chord length,pitch,camber and skew distributions in rotor optimization are the same as those of the seven-bladed propeller.An optimization design based on panel method and NSEA for the rotor is conducted to improve the rotor efficiency and reduce bearing forces.The optimized rotor is further evaluated by RANS simulation.The results show that the efficiency of the optimized rotor is 3.4% higher than that of the original rotor.And the pressure distributions on optimized rotor surface are more even than those on the original rotor.