چكيده به لاتين
Today, surface-piercing propellers have been recognized as a suitable choice for higher speeds. Yet, the development of design algorithms for such has been challenged by insufficient knowledge about the parameters affecting their performance. The geometry of surface piercing propeller has been designed experimentally, and no comprehensive studies are available for identifying the influential parameters to attain systematic formulations. One of the main challenges in the development of surface-piercing propellers is to identify the effects of geometric parameters on the performance. The main geometric difference between SPP and conventional propellers is its blade section shape. The blade section is of super cavity type with a sharp leading edge and thick trailing edge. Therefore, this research aims to evaluate the feasibility of presenting systematic relations between the geometric parameters of blade section and its hydrodynamic characteristics through combined methods of computational fluid dynamics and design of experiment and model testing.
In this regard, in the first step, the parametric geometry of the hydrolab base propeller (HL) is designed based on the cubic B-spline method. then a propeller family with different trailing edge (HL-Tx) and a propeller family with a different low pressure surface curve (HL –Sx) are generated according to the coordinates of control points based on the D-optimal response surface methodology. After that, in order to determine the performance of the base propeller, the model test method was used in the free surface open water tunnel. In this regard, the design, construction and in-situ calibration of a model test mechanism for SPP propellers was carried out based on the open loop water tunnel of the Iran University of Science and Technology, and the behavior of the HL001 propeller was investigated under different positional and operational parameters. Moreover, ventilation wake development at different Froude numbers was studied.
Based on the experimental data of this propeller, in order to investigate the effect of the trailing edge and the curve of the low-pressure surface of blade section on the performance of the propeller, the numerical simulation method of the propellers is based on URANS numerical simulation method in accordance with the two-phase VOF method and sliding mesh technique. The results of the simulation method are in good agreement with the experimental data. Finally, the quadratic regression models of hydrodynamic coefficients in terms of geometric variables have been statistically investigated by ANOVA method. ANOVA analyses of the quadratic regression models of HL-Tx series in terms of edge height (Y) and protrusion length (X), based on a 95% confidence interval, indicate these models have prediction adequacy of more than 90%. The main factor (X) is the only significant factor in both models. Increasing it will reduce the hydrodynamic coefficients. As a result, trailing edge variations can significantly affect torque and thrust coefficients by up to 40%, while efficiency changes are about 7%.
Also, the statistical analysis of the regression model of HL-Sx series, in terms of the three geometrical variables of the thickness of the leading edge (m), the thickness of the end curve (t) and the step (δ) show that the shape of the low-pressure surface curve has less effect on the performance of the propeller than The trailing edge is volatile. The maximum change in propeller hydrodynamic coefficients was 11% and the maximum effect on propeller efficiency was 7.5%. Also, the variance analysis of the regression equations indicates the existence of a cross-interaction relationship between the three geometric parameters and the existence of a nonlinear regression model with a prediction adequacy of 60%.
