Numerical assessment of propeller-hull interaction and propeller hub effects for a twin screw vessel

A numerical study that addresses twin screw propulsion was conducted and results using the RANS solvers ‘FreSCo+’ and ‘Fluent’ were shared. In order to avoid potential problems on property rights we combined the DTMB (David Taylor Model Basin) model No. 5415 and the SVA (Potsdam Model Basin) propeller No. CPP 1304. The computational self-propulsion point was identified via a numerical implementation of the so-called ‘British Method’. In this particular case, linked to the hub dimensions of the chosen propeller, the detailed modelling of the propeller hub and the true resolution of its connection to the hull was rather important. The same view holds for the propeller open water test setup. For the latter case we learned that the comparison with uncorrected experimental thrust data could represent a better way to confirm the numerical results

Behandlung der Profilkavitation durch Lösung einer singulären Fredholschen Integralgleichung 2. Art

Behandlung der Profilkavitation durch Lösung einer singulären Fredholschen Integralgleichung 2. Ar

Prediction of Tonal Underwater Noise Pattern from Cavitating Propellers with Special Attention to Ice Cover Effects

To predict underwater noise spectra associated to regular occurrence of propeller cavitation we have extended an existing method [1] (used for the prediction of fluctuating hull pressures) to become applicable for effects that are linked to a finite speed of sound. In [2] an intermediate approach was realized where (besides the hull) far field boundaries were introduced but the incompressible flow assumption was kept. However compressibility effects become noticeable in the far field, which may be judged to start at some 2-3 propeller-diameters distance from the centre of the cavitation events, if we confine to emissions at 1st-4th blade frequency. It was a logical continuation of our former efforts to realize a compressible flow model and integrate the propeller as a noise source. Having increased the functionality of our approach by referencing the speed of sound, the precision of the method was also somehow reduced. In our former approach, like in comparable approaches (see for instance [3] and [4]), the singularity system generating the near field propeller induced pressures involved various sources and vortices distributed on the propeller blades. With our current compressible approach this complexity was dropped, as a single point source substitutes the cavitating propeller. Such a simplification correlates with the assumption, that the monopole character of a noise source is decisive for the far field noise levels. In this contribution we outline the steps characterizing the procedure for predicting tonal underwater noise from cavitating propellers. In the first step a Vortex Lattice Method (VLM) is used to access the cavitation pattern on the propeller with special focus on the cavity volume attached to one blade. The second step accumulates the distributed cavities to establish a fluctuating point source of equivalent far field noise characteristic. As relevant limits the hull, the free surface, the sea bottom and an ice cover are introduced. Using finally a Boundary Element Method (BEM) approach the relevant noise characteristics are derived, accounting for external boundaries and for the finite speed of sound. The results provided here are focused on a comparative treatment of different scenarios, mainly addressing ice cover effects at finite the water depth

Design o combined propeller/stator propulsion system th special attention to scale effects

The design of a well performing pre-swirl stator (PSS) should strictly account for the full scale flow environment as met individually by each stator fin. In the European GRIP project an actual design has been delivered for a bulk carrier and was installed for trials. The results of the speed/power measurements could be compared to the trial data obtained 2 weeks earlier, when the stator was not mounted. The power gain with mounted stator was considerable. As the design was adapted to a computed full scale flow environment, the question arises whether such results could have been predicted prior by model tests performed with geometrical similar stator and propeller. For this purpose we analysed the model propulsion mode numerically. In summary the model scale analysis revealed considerable differences to the full scale setup, if the performance of the fins is compared individually. However in this numerical assessment of scale effects the overall decrease of power at the propeller showed only minor changes between model and full scale. The second question coming up after the trials have been completed addresses the propeller and its drop in RPM, an expected and forecasted result. Such an RPM change in itself will have a positive effect on the required power due to a reduction of viscous effects on torque. On the other hand due to requirements from the engine side it will usually be necessary to adapt the propeller geometry and compensate the RPM drop. It is investigated numerically, to what extent the required power will increase for such an RPM adapted propeller

Eine Methode zur Berechnung der Druckverteilung an Schiffspropellern mit Hilfe der instationären Tragflächentheorie und zur Kavitationsvorhersage nach einer quasistationären Theorie

Eine Methode zur Berechnung der Druckverteilung an Schiffspropellern mit Hilfe der instationären Tragflächentheorie und zur Kavitationsvorhersage nach einer quasistationären Theorie Kavitation tritt am Propeller auf, wenn die Flügelbelastung in einigen Bereichen des Blattes so groß wird, daß der Druck dort den Dampfdruck erreicht oder unterschreitet. Eine ihrer Erscheinungsformen ist die Schichtkavitation. Es bildet sich dabei ein Gasvolumen aus, das einen Teil des Flügels schichtförmig bedeckt. Andere Arten sind Spitzenwirbelkavitation, Blasenkavitation und Wolkenkavitation. In dieser Arbeit soll nur die Schichtkavitation behandelt werden. Ein Schiffspropeller arbeitet in der Praxis stets in einer räumlich inhomogenen Zuströmung. Deshalb sind Lage, Ausdehnung und Gesamtvolumen einer Kavitationsschicht von der WinkelsteIlung des betrachteten Flügels abhängig. Die Veränderlichkeit der Schicht verursacht Vibrationen am Hinterschiff. Die Außenhaut wird so zusätzlich belastet. Sollten die Vibrationen im hörbaren Bereich liegen, kann es zu erheblichen Lärmbelastungen innerhalb des Schiffes kommen. Zur Vermeidung dieser Effekte wäre es wünschenswert, die variable Geometrie und damit das variable Gesamtvolumen der Kavitationsschicht auch theoretisch zu erfassen. Ausgangspunkt für die Propellerkavitationsrechnung ist die Berechnung des Druckfeldes im kavitationsfreien Zustand. Hierzu existieren eine Reihe praktikabler Verfahren

The Effect of Propeller Scaling Methodology on the Performance Prediction

In common model testing practise, the measured values of the self propulsion test are split into the characteristics of the hull, the propeller and into the interaction factors. These coefficients are scaled separately to the respective full scale values and subsequently reassembled to give the power prediction. The accuracy of this power prediction depends inter alia on the accuracy of the measured values and the scaling procedure. An inherent problem of this approach is that it is virtually impossible to verify each single step, because of the complex nature of the underlying problem. In recent years the scaling of the open-water characteristics of propeller model tests attracted a renewed interest, fuelled by competitive tests, which became the norm due to requests of the customer. This paper shows the influence of different scaling procedures on the predicted power. The prediction is compared to the measured trials data and the quality of the prediction is judged. The procedures examined are the standard ITTC 1978 procedure plus derivatives of it, the Meyne method, the strip method developed by the Hamburgische Schiffbau-Versuchsanstalt (HSVA) and the β i -method by Helma