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Item type:Publication, Access status: with files , Einfluss von Maßstabseffekten auf die hydrodynamischen Eigenschaften von DüsenpropellernModel tests are carried out to test the hydrodynamic performance of ships, particularly for high-cost systems. However, these test are limited, as the test facilities and the test costs, which must be kept as low as possible, only permit comparatively large scales and consequently small models with low inflow velocities. In open water tests, the speeds must be adapted to the mechanical load limits of the measurement systems and propellers. Due to the resulting Reynolds number effects, a Reynolds number correction of the test results is necessary. When carrying out experimental investigations, the aim is to realize fully turbulent boundary layer flow on the test models. However, if the boundary layer is only partially turbulent in the model scale, new methods must be developed which allow the conversion of the hydrodynamic parameters as a function of the position of the laminar-turbulent boundary layer transition. Therefore, the development and further development of Reynolds number correction methods is of fundamental importance in model testing. The work presented here deals with the development of a Reynolds number correction method for open water test results of ducted propellers with accelerating nozzles. To isolate and better understand the physical effects, preliminary investigations were carried out using numerical flow calculations. Using a 2D- and a rotating 3D profile in a neutral, free-slip nozzle, the influence of the Reynolds number on the laminar/turbulent boundary layer and its effect on the drag and lift forces as well as the resulting relationships between lift and drag or propulsive force and torque were determined. CFD calculations of isolated propeller nozzles at different Reynolds numbers, in which the propeller effect was clearly defined by means of an actuator disk model, provided insights into the Reynolds number effects of the nozzles and their consequences for the propeller. It is shown that the formation of the boundary layer has a direct influence on the frictional and pressure forces. Four propellers were selected for systematic model tests and manufactured in two scales each (D = 200 mm and D = 350 mm) as controllable pitch propellers. The propeller hub was designed in such a way that different propeller diameters could be realized by means of spacer plates on the propeller blade feet and thus different gap dimensions between the propeller tip and the inside of the nozzle could be realized with a constant nozzle diameter. This made it possible to carry out extensive free-running and paint flow tests with the propellers with different pitch, gap dimensions and Reynolds numbers in the SVA-Potsdam towing tank. Since only a small Reynolds number range can be covered in model tests, comprehensive CFD calculations were carried out with ducted propellers for a wide Reynolds number range. The CFD calculations were validated on the basis of a large number of test results. Series calculations of geometrically different propellers in the Wag. 19A nozzle over a wide Reynolds number range generated a data basis for the development of an empirical Reynolds number correction model. This made it possible to determine the Reynolds number effects for 50 propellers with different area ratios, pitch settings, tip loads due to pitch and chord length, gap dimensions and skew distributions at different operating points. On the basis of this data, an empirical Reynolds number correction method for ducted propellers was developed for the most widely used Wag. 19A nozzle, in which both laminar-turbulent boundary layer effects and geometric propeller parameters are taken into account. The method makes it possible to determine the influence of the Reynolds number on the free running characteristics of ducted propellers as a function of geometric propeller parameters for the cavitation-free state.Publicationtype: Doctoral Thesis64 65 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Scale Effect on the Hydrodynamic Performance of a Ducted Propeller under Consideration of Flow Transition and Cavitation(2019-09); The paper presents a numerical investigation of the scale / Reynolds number effects on the hydrodynamic performance of a 4-bladed ducted propeller under open water test conditions. In the numerical simulations, the influences of flow transition and cavitation are taken into account. The RANS calculations are carried out using the ANSYS-CFX solver. For turbulence modelling, the Explicit Algebraic Reynolds Stress Model (EARSM) is applied in combination with the γ-Re θ transition model. The cavitation model employed is based on the Rayleigh-Plesset equation. In order to evaluate the various Reynolds number effects separately, different geometrical configurations are investigated. The first configuration is a 2D NACA66Amod hydrofoil. In this case, the investigation focuses on the laminar-turbulent flow-transition behaviour on the surface of the hydrofoil. In order to be able to study this behaviour on 3D geometries, a simplified blade geometry based on the hydrofoil mentioned above is developed and integrated in a neutral free-slip duct, which produces zero thrust. This configuration allows for investigating the flow transition at different regions of the rotating blade. Additionally, the flow on the Wageningen 19A duct is simulated in order to evaluate the scale effect on the hydrodynamic performance of the duct without considering scale influence induced by the propeller. In this case, the propeller flow is simulated using an actuator disc model. The final geometrical configuration is a ducted propeller that consists of a 4-bladed propeller in combination with the Wageningen 19A duct. The investigation of this configuration focuses on the change of the flow behaviour and the hydrodynamic characteristics over a wide range of Reynolds numbers. The influence of the Reynolds number on the thrust-torque ratio of the ducted propellers, particularly on the thrust breakdown behaviour at three propeller loads, is evaluated.Publicationtype: Conference Paper134 379