7.5-02-03-02.1, Revi- Benchmark Data Are Collected and Described Sion 01

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Table of Contents

3.3.6 Temperature ...... 7 Open Water Tests...... 2 3.4 Calibrations ...... 7 1. PURPOSE OF PROCEDURE ...... 2 3.4.1 General remarks ...... 7 2. PARAMETERS: ...... 2 3.4.2 Propeller dynamometer: ...... 7 3.4.3 Rate of revolutions ...... 8 2.1 Data Reduction Equations ...... 2 3.4.4 Speed ...... 8 2.2 Definition of Variables ...... 2 3.4.5 Thermometer ...... 8 3. PROCEDURE ...... 3 3.5 Test Procedure and Data Acquisition ...... 8 3.1 Model and Installation ...... 3 3.6 Data Reduction and Analysis...... 9 3.1.1 Model ...... 3 3.7 Documentation ...... 9 3.1.2 Installation ...... 3 3.2 Measurement Systems ...... 5 4. VALIDATION ...... 9 3.3 Instrumentation ...... 6 4.1 Uncertainty Analysis ...... 9 3.3.1 General remarks ...... 6 4.2 Benchmark Tests ...... 10 3.3.2 Thrust ...... 6 3.3.3 Torque ...... 7 5. REFERENCES ...... 10 3.3.4 Rate of revolution...... 7 3.3.5 Speed ...... 7

Updated by Approved

Propulsion Committee of 25th ITTC: 25th ITTC 2008

Date February 2008 Date 09/2008

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Open Water Tests

1. PURPOSE OF PROCEDURE T K = P TP ρ.nD24 The purpose of the procedure is to ensure Total thrust coefficient for a ducted propeller consistency of methodology and acquisition of unit correct results from Propeller Open Water K = K +K Tests. TT TP TD Propeller Efficiency in

The propeller open water characteristics are JKT Open Water η0 = used in the analysis of the Propulsion Tests and 2Kπ Q the estimation of the required power. The pro- VA cedure addresses model scale only and does not Advance Coefficient J = nD consider extrapolation and full scale prediction. Reynolds Number of propeller based on chord length 0.7 R The procedure is generally applicable for 1 open water tests performed with conventional Vc 2 + ()7.0 πnD 2 2 Re = 7.0 ()AR propellers, ducted propellers and tip-plate pro- ν pellers. For podded propeller open water test procedure please refer to 7.5-02-03-01.3- Podded Procedure Propulsor Tests and Extra- 2.2 Definition of Variables polation c0.7R Chord length at 0.7R (m) D Propeller diameter (m) 2. PARAMETERS: n Rate of revolutions of the model propeller (rps) 2.1 Data Reduction Equations Q Propeller torque (Nm) T R Propeller radius (m) Thrust Coefficient K = T ρ.nD24 T Propeller thrust (N) Q TD Duct (or nozzle) thrust (N) Torque Coefficient K = Q ρ.nD25 TP Ducted propeller thrust (N) TT Total thrust of a ducted propeller Ducted Propeller unit (N) V Speed of advance of the model propel- T A Duct Thrust Coefficient K = D ler (m/s) TD ρ.nD24 ρ Mass density of water (kg/m3) Ducted Propeller Thrust Coefficient υ Kinematic viscosity (m2/s)

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3. PROCEDURE The fairings forward and aft of a conventional pushing propeller should be modelled 3.1 Model and Installation according to Fig.1.

3.1.1 Model For a pulling propeller, the nose cone should be modelled accordingly. The model propeller should be manufac- tured in accordance with Standard Procedure 7.5-01-02-02, Propeller Model Accuracy.

Figure 1 Geometry of Model Fairings

cient length to ensure that the inflow over the 3.1.2 Installation propeller hub is parallel to the shaft should be mounted upstream of the propeller model, 3.1.2.1 Conventional Propellers Fig.1. In the case of a pulling propeller, the nose cone should be modelled according to the 3.1.2.1.1 Towing Tank actual propeller geometry. The connection between the cap and the hub should be smooth The propeller model is to be mounted on a and without a gap. The size and shape of the drive shaft. A streamlined nose cap of suffi- nose cap should be recorded. In some cases the

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nose length may be less than 1.5 D as long as shaft should be arranged parallel to the calm the flow is parallel. water surface and the carriage rails. A typical set up for a towing tank is shown in Fig. 2. In order to eliminate a pressure build-up at the downstream end of the hub and the fixed The propeller immersion has to be selected shaft housing, the rotating part of the hub such that air drawing from the water surface is should be positioned in such a way to avoid avoided at any test condition. As a guideline, any kind of pressure build-up. The arrangement an immersion of the propeller shaft of at least used should be recorded and included in the 1.5 D is recommended, where D is the diameter test report. of the propeller. The immersion of the shaft centre line should be recorded and included in The drive shaft housing should not be too the test report. close to the model propeller blades. A distance of not less than 1.5 D to 2.0 D is recommended, where D is the propeller diameter. The drive

Distance

Immersion

Cu rren t Meter Propeller Dynamometer Diameter Figure 2 Typical Set Up for Tests on Conventional Propellers in a Towing Tank

Distance Load Cell

Strut Immersion

Cu rren t Meter Duct

Diameter Propeller D ynam ometer

Figure 3 Typical Set Up for Tests on Ducted Propellers in a Towing Tank

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3.1.2.2 Ducted Propellers When a current meter is used to measure the speed of advance of the propeller model, The clearance between the propeller tips the immersion of the current meter should cor- and the inner surface of the duct should be kept respond to the immersion of the propeller shaft. at the recommended design value. Depending The distance between the propeller and the on model scale, this value sometimes cannot be current meter should be selected to ensure that achieved. Then, a maximum of 1.0 mm clear- the propeller model is not influenced by the ance for a scaled model propeller of about current meter. A distance between the current 250mm diameter is considered to be satisfac- meter and propeller model of at least 10 D is tory. The relative longitudinal position of the recommended, where D is the diameter of the propeller and the duct should be adjusted to the model propeller. design value.

The dimensions of the tank should be large The duct is usually supported by a strut enough to avoid blockage and should be in- which has a streamlined section shape. Only cluded in the test report. the force acting on the duct should be measured during the test. A typical set up for a towing 3.1.2.1.2 Cavitation Tunnel tank is shown in Fig.3. The set-up for a cavitation tunnel is similar to that for a towing tank. The propeller model is to be mounted on a drive shaft. A streamlined nose cap of suffi- The duct thrust is usually measured by a cient length to ensure that the inflow over the load cell with a shielded strut, or a strain gauge propeller hub is parallel to the shaft should be positioned between the duct and the strut. An- mounted upstream of the propeller model, other method is to measure the drag force act- Fig.1. The connection between the cap and the ing on the strut separately as a function of ad- hub should be smooth and without a gap. The vance velocity. size and shape of the nose cap should be recorded. In some cases the nose length may be 3.2 Measurement Systems less than 1.5 D as long as the flow is parallel to the shaft axis. The choice of propeller diameter Fig 4. shows the scheme of a typical meas- should be made such that scaling effects are uring system avoided within the blockage constraints of a given cavitation tunnel. The following quantities are measured: • Model speed The dimensions of the cavitation tunnel • Propeller thrust should be included in the test report. For test- • Propeller torque ing in the cavitation tunnel significant cavita- • Propeller rate of revolution tion should be avoided and open water tests • Duct thrust (if fitted) should be carried out under atmospheric condi- • Water temperature (for calculation of tion. viscosity)

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ENVIRONMENTAL CARRIAGE PROPELLER DUCT/POD CONDITIONS

SPEED TEMPERATURE PROPELLER MEASUREMENT DYNAMOMETER MEASUREMENT DYNAMOMETER TACHOMETER/ THERMOMETER PROBE

THRUST, DUCT /POD TANK WATER MODEL SPEED TORQUE, THRUST TEMPERATURE RATE OF REVOLUTION

SIGNAL CONDITIONING and DATA ACQUISITION

COMPUTER

Figure 4 Typical Measurement System

3.3 Instrumentation 3.3.2 Thrust

3.3.1 General remarks The propeller thrust is measured using the propeller open water dynamometer. In the case The performance of a propeller open water test when the propeller is working in a nozzle, the requires the use of a propeller open water dy- additional thrust or the resistance of the nozzle namometer which enables the measurement of has to be considered. thrust, torque and rate of revolution of the propeller. The quoted bias accuracies are for in- The thrust dynamometer should measure dicative purposes only. Uncertainty analysis the thrust to within 0.2% of the maximum ca- should be used to derive the actual require- pacity of the dynamometer. This does not nec- ments.

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essarily imply that the thrust itself is measured 3.4 Calibrations to within the same tolerance of its true value. 3.4.1 General remarks 3.3.3 Torque All devices used for data acquisition should The propeller torque is measured using the be calibrated regularly. For calibration, the propeller open water dynamometer. In the measured quantities should be either substi- torque measurement, it is essential to keep the tuted by calibrated weights and pulses or shaft friction losses as low as possible. checked by other measuring devices which have already been calibrated. Calibration dia- The torque dynamometer should measure grams, where the measured quantities (output the torque to within 0.2% of the maximum ca- values) are plotted against the calibration units pacity of the dynamometer. This does not nec- (input units), may be useful to check the cali- essarily imply that the torque itself is measured bration itself, as well as the linearity of strain to within the same tolerance of its true value. gauge or inductive instruments. Calibration should generally be in accordance with ITTC 3.3.4 Rate of revolutions Recommended Procedure 7.6-01-01.

The rate of revolutions of the propeller Calibrations should preferably include as should be constant throughout the test run. much of the measurement chain as possible Steadiness of the rate of revolution is essential (amplifier, filter, A/D converter). If the check in achieving reliable results. indicates that the required accuracies cannot be met, the calibration should be renewed or the The measurement instrumentation should instrument replaced and the check repeated. measure the rate of revolutions to within 0.2% Daily checking of a pulse counter for speed of the maximum rate of revolutions. This does measurements is usually not required. Instead, not necessarily imply that the rate of revolu- the check on this device is covered by calibrations itself is measured to within the same tol- tions carried out at regular intervals. erance of its true value. 3.4.2 Propeller dynamometer: 3.3.5 Speed 3.4.2.1 Propeller Thrust The speed of the propeller model should be measured to within 0.1% of the maximum car- The calibration of the propeller open water riage speed or within 3 mm/sec, whichever is dynamometer in respect of the propeller thrust the larger for towing tanks. In cavitation tun- should be carried out statically and, if possible, nels the speed should be measured within 1% dynamically with calibrated weights. The dy- of the maximum tunnel axial speed. namic calibration should be carried out at vari- ous rates of revolution. 3.3.6 Temperature

The water temperature should be measured at the propeller shaft level using a thermometer.

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3.4.2.2 Propeller Torque sure no drift has occurred. The range of measurements should cover that of the open water The calibration of the propeller open water tests in terms of rotational speed and speed of dynamometer in respect of the propeller torque advance. The way these measurements are car- should be carried out statically and, if possible, ried out, and the results, should be recorded. dynamically. For the static calibration, calibrated weights are applied to a lever of known In the case of pulling propellers (where the length to simulate a moment on the dyna- propeller is ahead of a bossing) the influence of mometer shaft. The dynamic calibration should the propeller cap on the thrust and torque of the be carried out, for example, by use of an eddy propeller is not relevant, as the propeller is current brake tested in the same configuration as that used behind the ship. 3.4.3 Rate of revolution During each open water test run, the values The calibration of the respective devices of thrust, torque, rate of revolution and speed should be carried out by use of precise motor of advance are recorded simultaneously. When speed transmitters. the propeller works in a nozzle, or is designed to be used on pods or conventional Z-drives, 3.4.4 Speed the forces of such devices in the direction of the propeller shaft should also be measured. The calibration of the carriage speed or tunnel axial speed will depend mainly on how The range of advance coefficients should the speed is measured in each facility. The cover the range from J = 0 until KT < 0, in or- speed should be checked regularly and respec- der to determine accurately the point at which tive records should be stored. KT = 0.

3.4.5 Thermometer There should be sufficient waiting time between consecutive runs in order to achieve Thermometers should be calibrated accord- similar conditions and to obtain consistent re- ing to common standards and/or following the sults. This waiting time will depend on the size advice of the manufacturer. and type of model, model speed and test facility. The waiting times should be recorded. 3.5 Test Procedure and Data Acquisition The propeller open water tests should be Prior to the tests, runs should be made to conducted at least at two Reynolds Numbers; measure the influence of the streamlined nose one should be at the Reynolds Number used for cap. These measurements should be carried out the evaluation of the propulsion test, which with a propeller hub without blades, having the should be not lower than 2.105 and the other same shape as the real propeller hub. This hub should be as high as possible. should have the same weight as the propeller. Before and after each test series, the zero refer- ence values of thrust and torque are determined. Zeros should be checked between runs to en-

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3.6 Data Reduction and Analysis Immersion of centreline of propeller shaft in the case of towing tank The model data derived from the experi- • Particulars of the towing tank or cavitation ment, namely thrust, torque and rate of revolu- tunnel, including length, breadth and water tion, should be plotted against the speed of ad- depth or test section length, breadth and vance. The measured thrust and torque are to height. be corrected for the effect of the streamlined nose cap, as determined before and/or after the • Test date actual open water test. In the case of cavitation • Parametric data for the test: tunnel experiments the measured velocity, Water temperature thrust and torque values are corrected for tun- Water density nel wall effects based on the work of Wood and Kinematic viscosity of the water Harris. The respective curves should be faired Reynolds Number (based on propeller and the model values corresponding to required blade chord at 0.7R) speeds of advance should be taken from the • For each speed the following data should be diagram. given as a minimum: Thrust and torque of the propeller The measured duct force (resistance or Rate of revolution thrust) should be corrected for the effect of the Force of nozzle in the direction of the (streamlined) support strut, as determined be- propeller shaft fore or after the actual open water test.

Values of water density and viscosity 4. VALIDATION should be determined according to ITTC Rec- ommended Procedure 7.5-02-01-03. 4.1 Uncertainty Analysis

The required values of KT, (KTD), KQ, η0 Uncertainty analysis should be performed and J are calculated according to the data re- in accordance with Uncertainty Analysis in duction equations given in Section 2.1. EFD, Uncertainty Assessment Methodology as described in QM 7.5-02-01-01 and Uncertainty 3.7 Documentation Analysis in EFD, Guidelines for Uncertainty Assessment as described in QM 7.5-02-01-02. The results from the test should be collated In addition to the above, an example Uncer- in a report which should contain at least the tainty Analysis Example for Propeller Open following information: Water Test is provided in ITTC Recommended • Model Propeller Specification: Procedure 7.5-02-03-2.2. Identification (model number or similar)

Model scale Main dimensions and particulars (see recommendations of ITTC Recom- mended Procedure 7.5-01-01-01 Ship Models)

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4.2 Benchmark Tests Conference, Venice, Italy, ITTC Recom- mended Procedure 7.5-02-03-02.1, Revi- Benchmark data are collected and described sion 01. in ‘Benchmark Database for CFD, Validation (2) Wood and Harris, 1920, Some Notes on the for Resistance and Propulsion, QM 7.5-03-02- Theory of an Airscrew Working in a Wind 02 Channel, Aeronautical Research Council, R&M 662. 5. REFERENCES (1) ITTC 2002, Propulsion, Propulsor Open Water Test, 23rd International Towing Tank