Propulsion @en

Ducted Propellers

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A nozzle is a hydrodynamically optimised shell encircling the blade tips of a propeller. The combination of propeller and nozzle is called a ducted propeller. There are two types of nozzles, the acceleration and the deceleration nozzle. The deceleration nozzle causes a reduction in flow velocity and an increase in pressure in the propeller plane. Deceleration nozzles are therefore used to reduce the cavitation risk for fast ships.

The accelerating nozzle causes an increase in flow velocity and hence a discharge of the propeller. Ducted propellers with an acceleration nozzle are used for highly loaded propellers and propellers with restricted diameters.

Since its foundation in 1953, the SVA Potsdam has been working on the development and optimisation of ducted propellers for inland and fishing vessels as well as tugs as well as thrusters. In addition to conventional ducted propellers (Wageningen, Schuschkin, OST), unconventional, partially integrated nozzle and controllable pitch propellers have been studied extensively in particular.

Based on a series of tests in the context of an R & D project with a combination of propellers of the Wageningen B-series and OST nozzles, polynomial coefficients were developed for ducted propeller systems with OST nozzles [10]. At lower thrust loads, the OST nozzle profile increases the mass flow through the propeller disc and causes a jet expansion at the nozzle outlet. The characteristics of ducted propellers with OST nozzles can be calculated with polynomial coefficients and used for propulsions prediction.

In the field of CFD calculation, research projects were conducted in close cooperation with ANSYS Germany GmbH for ducted propeller calculation. Based on the developed methods, systematic numerical calculations of ducted propellers were implemented in the R & D project “Correlating Z-Drives with Nozzles” to develop a method for Reynolds number correction (conversion of model test results to the full-size version).

The continued development and validation of the bollard pull and propulsion prediction for tugs with large power capacity has been the subject of R & D projects and industry projects. In the R & D projects “Increasing the Design Safety of Ducted Propeller Systems at Bollard Pull Conditions” and “Reynolds Number Effects on Bollard Pull Predictions” [5], [6] the influences of cavitation and scale on the bollard pull of tugs with ducted propellers were presented in detail. With these results, the risk of thrust break down of ducted propeller can be found in the design stage.

In the R & D project “Forecasting Reliability for the Power Requirement of Tugs with Ducted Propeller Systems”, GeoSim tests and calculations were carried out for tugs at the point of propulsion. The results of these studies have been incorporated into the propulsion forecasting methods for ships with ducted propellers.

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Context Related References / Research Projects

[1] Abdel-Maksoud, M.: Convergence Study of Viscous Flow Computations Around a High Loaded Nozzle Propeller, Numerical Towing Tank Symposium NuTTS 2000, Tjärnö, Sweden, September 2000
[2] Abdel-Maksoud, M., Heinke, H.-J.: Scale Effects on Ducted Propellers, 24th Symposium on Naval Hydrodynamics, Fukuoka, Japan, July 2002
[3] Gutsche, F.: Düsenpropeller in Theorie und Experiment, Jahrbuch der STG, Bd.53, 1959
[4] Heinke, H.-J., Philipp, O.: Development of a skew blade shape for ducted controllable pitch propeller systems”, Proceedings, PROPCAV’95, Newcastle, 1995
[5] Heinke, H.-J., Hellwig, K.: Aspekte der Pfahlzugprognose für Schlepper großer Leistung, 104. Hauptversammlung der STG, Hamburg, November 2009
[6] Mertes, P., Heinke, H.-J.: Aspects of the Design Procedure for Propellers Providing Maximum Bollard Pull, ITS 2008, Singapore, May 2008
[7] Philipp, O., Heinke, H.-J., Müller, E.: Die Düsenform – ein relevanter Parameter der Effizienz von Düsen-Propeller-Systemen, STG-Sprechtag „Hydrodynamik schneller Schiffe und ummantelter Propeller“, Berlin, Potsdam, September 1993
[8] Philipp, O., Heinke, H.-J., Binek, H.: Contribution of Hydrodynamics for the Calculation of Ducted Units for Ships at Shallow Water, HYDRONAV’ 95, Gdansk, November 1995
[9] Schroeder, G.: Wirkungsgrad von Düsenpropellern mit unterschiedlicher Düsen- und Propellerform, Schiffbautechnik 17 (1967) 8
[10] Schulze, R., Manke, H.: Propellersysteme mit Ostdüsen, HANSA, 137 (2000) 2

Frictional Resistance Measurement

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The frictional resistance of a ship is a substantial part of the total resistance. This is influenced, among other things, by the texture of the skin (e.g., type of coating, degree of fouling). To minimise the power consumption and thereby reduce costs and protect the environment, it is therefore sensible to hold frictional resistance as low as possible by special coatings or surface structures. Corresponding studies can be performed on the friction measuring system. A roughness analysis of the surface by itself is not sufficient to deduce the exact frictional resistance. Experimental studies allow for more accurate conclusions. For this purpose, two plates with the coating to be tested are installed so that these form a narrow rectangular channel which is traversed by water in the friction test section. By the simultaneous measurement of the flow rate and the pressure loss along the test section and the water temperature, the wall shear stress can be detected and finally the frictional resistance coefficient of the plates is calculated. The results are transferrable to the frictional resistance of the ship. In order to cover the largest possible range of speeds, up to 20 m/s can be run in the friction measuring system.

These studies are not limited to the shipbuilding industry, but are also applicable in the aerospace and automotive industries. The results from the friction measuring system are also transferrable for these applications and can be profitably implemented where friction plays a role.

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Context Related References / Research Projects

[1] Schulze, R.: Measurement of Skin Friction Drag and Design of Riblet Structures for a Ship Application, AIRBUS, Bremen, 30. Juni 2015

Potsdam Propeller Test Case PPTC

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The Potsdam Propeller Test Case (PPTC) is a program for the validation of calculation methods for propellers. The PPTC propeller has been specially designed to enable researchers to validate calculation methods for propeller cavitation. The SVA design VP1304 (PPTC-Propeller) has, beside good hydrodynamic qualities, pronounced tip vortices, suction side and pressure side cavitation, root and bubble cavitation, and therefore is well suited for validation purposes.The open water characteristics of the propeller were measured at 0 ° and 12 ° shaft inclination. In selected points of operation the cavitation was recorded on the propeller optically. Additionally, extensive velocity measurements in the area of the blade tip as well as pressure fluctuation measurements were carried out. Within the framework of the International Symposium on Marine Propulsion in 2011 and 2015 respectively, a workshop has been organised on cavitation and propeller performance. In these workshops, the results of calculations from different tools were presented, analysed, and discussed and also compared with the experimental results.

For both workshops, the geometries, measurements, evaluations, reports and presentations are available on the website of the SVA (smp’11 and smp’15). The Proceedings of smp’11 and smp’15 also include presentations of the 1st and 2nd Workshop on Cavitation and Propeller Performance (www.marinepropulsors.com). The PPTC is also used by the ITTC as a benchmark for propeller calculations.

PPTC leads to various published data on the Potsdam Propeller Test Case and related projects.

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Context Related References / Research Projects

[1]    smp’11: 2nd Symposium on Marine Propulsors & 1st Workshop on Cavitation and Propeller Performance, June 17 -18, 2011, Hamburg, Germany
[2]    smp’15: 4th Symposium on Marine Propulsors & 2nd Workshop on Cavitation and Propeller Performance, May 31 – June 4, 2015, Austin, Texas, USA

PIV – Particle Image Velocimetry

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PIV is a method for measuring velocity fields in fluids. The process is purely visual and is therefore a non intrusive measurement method; the flow to be examined is not affected. The measurement of the velocity field is based on the determination of the displacement of particles (bubbles, seeding particles) in the flow by distance Δs within a period Δt. The shift Δs is detected by two photographic images of the particle images which are received in a very short time interval Δt. To this end the particles in the fluid are illuminated by very short laser flashes. From the displacement of the particle images in the period Δt the velocity vectors of the fluid at the position of the particles can be calculated using stochastic methods. By using two cameras with stereoscopic recording, a three-dimensional flow field can be determined, i.e., all three velocity components are then available in the measuring range.

The process is very versatile. So far the following measuring tasks, among others, have been undertaken:

  • Flow fields in the wake of ship models with and without working propellers
  • Rudder dynamics with gap flow
  • Decay of vortices on a generic wing
  • Vortex flow around bilge keels
  • Propeller wash of a thruster on a semi-submersible platform
  • Propeller wash in the cavitation tunnel
  • Flow around and wake of a submarine model with tower
  • Flow around profile sections in the cavitation tunnel

With PIV the whole velocity field is measured in every frame. From the individual recordings the transient evolution of the flow can be visualized and also a mean velocity field can be determined by averaging all recordings. The desired spatial resolution determines the size of the field of view and the achievable number of vectors in the measuring range. The largest achieved measuring range so far had an extension of approximately 400×600 mm, in this case about 6000 vectors. For this task, a stereoscopic PIV system from the company TSI is used. It has a modular design, so that all symmetrical, asymmetrical and independent arrangements of cameras and light sheet can be realized. Thus, for example, it is possible to measure the full depth of the towing tank.

Please read more about the technical specifications of this PIV system here.

 

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Context Related References / Research Projects

[1]    Anschau, P.: Stereoskopische PIV-Messungen in Schlepprinne und Kavitationstunnel, Workshop Optische Strömungsmessverfahrenr, TU Dresden, 9. März 2011
[2]    Anschau, P.: Stereoskopische PIV-Messungen an tiefgetauchten Schleppkörpern, TSI Seminar , Potsdam, 17. Oktober 2012
[3]    Kleinwächter, A., Hellwig-Rieck, K., Ebert, E., Kostbade, R., Heinke, H.-J., Damschke, N. A.: PIV as a Novel Full-Scale Measurement Technique in cavitation Research, Fourth International symposium on Marine Propulsors, smp´15, Austin, Texas, USA, June 2015

ESD – Energy Saving Devices

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The term “Energy Saving Device” (ESD) encompasses the measures and methods for saving energy in ship operation compared to “conventional” ships. ESDs include, among other things, the asymmetric after-body (“stern bulb” form), propeller, nozzles, guide fins, and the rudder, alone and in combination.
The development of ESDs has been worked on already since the 70s. The focus was on the influence of after-body forms and bulges, propulsion and vibration excitation, design and testing of contra-rotating and overlapping propellers, and developing inflow-improving nozzles [1], [2], [3].
Asymmetric after-bodies and guide fins were used in the context of propulsion optimisation of ships for generating a pre-swirl in the propeller inflow to reduce the rotational losses of the propeller. The research and development in this area led to the SVA guide fin systems. Model tests with different types of ships and full-scale measurements show a potential of 2 to 5 % power savings through the use of SVA guide fin systems [4], [5], [6]. Various R & D projects have been processed in order to improve the design of propellers and ESDs. Potential flow methods are used for the design and optimisation of propellers. Viscous calculation methods and experiments are used to verify the design, the prognosis of scale effects and applied to the design and optimisation of propulsion systems such as ducted propellers, thrusters and ESDs. To check the design of the propeller, speed measurements are performed on propeller boss cap fins and rudder. The SVA-developed HVV outlet cover (Hub Vortex Vane), leads to a reduction of the hub vortex and reduces the energy loss of the propeller in the hub area.Systematic CFD calculations are performed for analysis of the effectiveness of Costa Bulb on rudder and to derive design cues [7]. These works were continued in R & D project BossCEff – “Increasing the Effective Degree of Propulsion and Controlling Boss Vortex Cavitation Through Improved Consideration of the Interaction Between Propeller Wash and Boss Cover” [8], [9]. In cooperation with the project partners Technical University of Hamburg-Harburg, The Institute of Fluid Dynamics and Ship Theory (FDS), and the Mecklenburger Metallguss GmbH (MMG), special propeller flow caps were developed and studied for use in rudders with Costa Bulbs and propeller boss covers with fins.

The Mecklenburg Metallguss GmbH developed in the collaborative projects BossCEff a new energy-saving propeller cap, MMG ESCAP®.

The propeller caps improve propulsion characteristics of the vessel on existing propellers and on propeller redesign projects. The ESCAP®, among others, has also been successfully applied in newly designed propellers.

The following maximum power savings were achieved for ships with ESDs by investigations of SVA [11], [12]:

– Twisted Rudder up to 1,4 %
Costa-Bulb with Twisted Rudders up to 3,7 %
Costa-Bulb with Conventional Rudders up to 3,5 %
Boss Cap Fins up to 3,2 %
Propeller Redesign up to 14 %
Wake Equalising Duct up to 4,8 %
Becker Mewis Duct® up to 10 %
Bulbous Bow Retro-fit up to 21 %

 

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Context Related References / Research Projects

[1] Schmidt, D.: Propulsionsuntersuchungen mit Einzelpropeller und Gegenlaufpropeller am Modell eines Containerschiffes, Schiffbauforschung 14 1/2/1975
[2] Schmidt, D.: Der Einfluss der Form des Heckwulstes auf die Schwingungserregung durch den Propeller für ein Containerschiff, Schiffbauforschung 21 1/1982
[3] Schmidt, D.: Die Reduzierung der propellererregten Schwingungen durch nachstrombeeinflussende Änderungen am Hinterschiff,
Schiffbauforschung 23 3/1984
[4] Mewis, F., Peters, H.-E.: Verbesserung der Propulsion durch ein neuartiges Flossensystem Intern. Rostocker Schiffstechnisches Symposium, Schiffbauforschung, Sonderheft, Bd. 1, 1987
[5] Peters, H.-E., Mewis, F.: Das Leitflossensystem der SVA am Containerschiff Typ Saturn, HANSA Nr. 17/18, 1990
[6] Schmidt, D.: Nachrüstung von Motorgüterschiffen ermöglicht Leistungseinsparung, Binnenschiffahrt – ZfB Nr. 9, Sept. 1995
[7] Lübke, L.: Numerical Simulation of the Viscous Flow around Costa Bulbs, NUTTS 2002, Nantes, August 2002
[8] Greitsch, L., Pfannenschmidt, R., Abdel-Maksoud, M., Druckenbrod, M., Heinke, H.-J.: BossCEff – Steigerung des Propulsionswirkungsgrades durch Reduktion von Nabenwirbelverlusten, Statustagung „Maritime Technologien“, BMWE, Rostock, 10.12.2014
[9] Heinke, H.-J., Lübke, L. O., Steinwand, M.: Numerical and experimental investigations for influencing the propulsion efficiency in the hub region of the propeller, STG-Sprechtag “Hydrodynamic Performance of ESDs”, Hamburg, 09.10.2014
[10] Pfannenschmidt, R.; Greitsch, L.: Das MMG Re-Design-Programm, Hanse Sail Business Forum, 07.08.2014
[11] Heinke, H.-J., Lübke, L. O.: Maßnahmen zur Energieeinsparung, Schiff & Hafen, Nr. 10, 2014
[12] Heinke, H.-J., Hellwig-Rieck, K.: Investigation of Scale Effects on Ships with a Wake Equalizing Duct or with Vortex Generator Fins, Second International Symposium on Marine Propulsors, smp’11, Hamburg, Germany, June 2011