英語翻譯
As mentioned above,when the velocity on the duct induced by propeller is computed,two different treatments are applied.Fig.4 gives the comparison of results obtained by two treatments,in which“CAV”and“NAV”denote circumferentially averaged and not averaged treatments respectively.It is seen from Fig.4 that the thrust of duct at lowadvance coefficient can be improved when the induced velocity of propeller to duct is not circumferentially averaged,namely the wake behind the duct exists.This conclusion is coincident with that from Ref.[7].
In Figs.5 and 6,parameter BTKI is a coefficient determining the hydrodynamic pitch angle in the transition region of the wake of propeller.Usually BTKI=0.5 is adopted by panel method for the single propeller.It can be seen from Figs.5 and 6 that BTKI=0.43 gives better results for the case of JD7704 duct+KA propeller series and BTKI=0.48 for the case of JD7704 duct + JDC propeller series.
In the numerical calculations of panel method,the trialing wake sheet of the propellerand duct are truncated at certain distance behind the propeller or duct.Fig.7 shows that reasonable results can be obtained when transition wake range of the propeller is 1080 degrees.It is found from the Fig.8 that the numerical result becomes converged gradually with the increment of region of trailing vortex wake of duct,and there will be no effect on the thrust of duct if the wake length of the duct is over four times of the length of the duct,which will be used in the following calculations.Fig.9 shows that the contraction coefficient of the transition wake of the propeller,RW0,makes no influence on the calculated results,even RW0=0.83,0.98 or 1.0 (“No Contra”in the figure).RW0=0.83 is adopted in the present paper.