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This study investigates the experimental parameters of particle image velocimetry (PIV) to enhance the measurement technique for turbulent flow fields around a circular cylinder at a Reynolds number (Re) of 1.4×105. At the Korea Research Institute of Ships & Ocean Engineering (KRISO), we utilized the cavitation tunnel and PIV system to capture the instantaneous flow fields and statistically obtained the mean flow fields. An aspect ratio and blockage ratio of 16.7% and 6.0%, respectively, were considered to minimize the tunnel wall effect on the cylinder wakes. The optimal values of the pulse time and the number of flow fields were determined by comparing the contours of mean streamlines, velocities, Reynolds shear stresses, and turbulent kinetic energy under their different values to ensure accurate and converged results. Based on the findings, we recommend a pulse time of 45 μs corresponding to a particle moving time of 3–4 pixels, and at least 3,000 instantaneous flow fields to accurately obtain the mean flow fields. The results of the present study agree well with those of previous studies that examined the end of the subcritical flow regime.

Hydraulic turbines contribute to 60% of renewable energy in the world; however, they also entail some adverse effects on the aquatic ecology system. One such effect is their excessive noise and vibration. To minimize this effect, one of the most effective and feasible solutions is to modify the design of the turbine rotor blade by introducing a skew. In this study, two 0.3-meter tidal turbines with 0-degree (no-skewness) and positive 90-degree skewness made of stainless steel 316L were designed and printed using a 3-D printing powder bed fusion technique. These rotors were then tested at the Emerson Cavitation Tunnel (ECT) at Newcastle University, UK, and the variation in the skewness of the blades of the turbines as a function of the power coefficient on a given tip speed ratio (TSR) value was ascertained. Results showed that the highly skewed rotor had significantly lower drag and torque fluctuations, with a slight decrease in efficiency compared to the non-skewed one, which warrants further investigation on the effect of added skew to reduce vibration and noise. Numerical simulations were also performed for verification and validation of the experimental tests, using the H45 dynamometer at the ECT. A comprehensive software code for propellers and tidal turbines, ROTORYSICS, was used to examine the cavitation effect of the two rotors; a comparison was made for both, with and without cavitation. The results indicate that for a high immersion depth of tidal turbine rotors, cavitation rarely occurs, but for hydrokinetic turbines that are installed on dams in rivers and falls, cavitation could be a serious concern. It was concluded that the 0-degree skewed rotor is more hydrodynamically efficient than the 90-degree skewed rotor. [ABSTRACT FROM AUTHOR]

The objective of the present study is to investigate by model tests the erosion caused by blade root cavitation for a set of three marine propellers. Experiments have been carried out using soft paint technique together with cavitation observations in the UNIGE cavitation tunnel. Three standard cameras and one high speed camera have been used to observe the damage patterns and cavitation dynamics, respectively. Standard cameras are fixed on the top of test section to continuously monitor the effect of erosion damage on the blade root, the high-speed camera has been placed at different positions to investigate detailed evolution and collapse of bubbles on pressure and suction side of propeller blades. Soft paint results showing damages pattern have been analysed simultaneously with the high speed videos, and showed remarkable agreement between the occurrence of damage on the blades and the bubble collapse of cavitation. The proposed methodology allows comparing different propellers in terms of cavitation aggressiveness. The comparison of these results with full-scale data provides useful indications to propeller designers when root cavitation cannot be avoided. • Cavitation dynamics of three different model scale propellers working in inclined shaft configuration. • Soft paint tests to study the damage patterns on suction and pressure side of propeller blades. • Experiments are carried out using three standard cameras and one high speed camera simultaneously to correlate the damage patterns and cavities dynamics. • Results exhibited remarkable agreement between the occurrence of damage on the blades and the bubble collapse of cavitation. [ABSTRACT FROM AUTHOR]

This article deals with the numerical simulation of unsteady cavitating flow around hydrofoils, supported by experimental research realized in a cavitation tunnel situated in the Centre of Hydraulic Research. Two straight NACA hydrofoils (NACA0020 and NACA2412) were employed. The comprehensive unsteady CFD analysis was based on scale-resolving simulations (hereinafter SRS) with the aim of capturing correctly the interactions between the cavitation structures and re-entrant flow as well as the compressibility and thermal effects of cavitation. The static pressure fluctuations during the cavity oscillation cycles and the evaporation and condensation processes are discussed in detail. To predict correctly the high-pressure peaks during the bubble cloud collapses and the pressure pulse propagation speed, the real properties of water and the mixture total energy conservation equation were considered. In addition, the estimated content of undissolved air was taken into account. The numerical simulations were validated by means of already published experiments or compared with experiments conducted by the authors, and with good agreement. [ABSTRACT FROM AUTHOR]

Hydraulic turbines contribute to 60% of renewable energy in the world; however, they also entail some adverse effects on the aquatic ecology system. One such effect is their excessive noise and vibration. To minimize this effect, one of the most effective and feasible solutions is to modify the design of the turbine rotor blade by introducing a skew. In this study, two 0.3-meter tidal turbines with 0-degree (no-skewness) and positive 90-degree skewness made of stainless steel 316L were designed and printed using a 3-D printing powder bed fusion technique. These rotors were then tested at the Emerson Cavitation Tunnel (ECT) at Newcastle University, UK, and the variation in the skewness of the blades of the turbines as a function of the power coefficient on a given tip speed ratio (TSR) value was ascertained. Results showed that the highly skewed rotor had significantly lower drag and torque fluctuations, with a slight decrease in efficiency compared to the non-skewed one, which warrants further investigation on the effect of added skew to reduce vibration and noise. Numerical simulations were also performed for verification and validation of the experimental tests, using the H45 dynamometer at the ECT. A comprehensive software code for propellers and tidal turbines, ROTORYSICS, was used to examine the cavitation effect of the two rotors; a comparison was made for both, with and without cavitation. The results indicate that for a high immersion depth of tidal turbine rotors, cavitation rarely occurs, but for hydrokinetic turbines that are installed on dams in rivers and falls, cavitation could be a serious concern. It was concluded that the 0-degree skewed rotor is more hydrodynamically efficient than the 90-degree skewed rotor.

The experimental and numerical investigation of unsteady cavitating flow around a NACA2412 hydrofoil with chemically treated surfaces is described. The study was focused on the influence of the surface wettability on the intensity of cavitation processes. Two steel hydrofoils whose surface is treated using different methods are compared with a hydrofoil having a nontreated surface. The first of the treated hydrofoils has a 50–70-µm thick wear-resistant hydrophobic coating of tungsten carbide applied by ion-plasma deposition in a vacuum chamber. The second hydrofoil has a coating of a surfactant, octodecyamine, applied by deposition while keeping the hydrofoil in an aqueous solution. The hydrofoil with the span/chord ratio of 1.25 was tested in the cavitation tunnel. The incidence angle of the hydrofoil to the incoming flow was 8°. Numerical results were obtained using the ANSYS CFX software package with the Zwart cavitation model and the SAS-SST turbulence model. The monitored pressure fluctuations and the level of noise generated by cavitation-induced unsteady processes are estimated. It is demonstrated that additional surface treatment can help prevent unwanted phenomena in the flow path caused by cavitation. This technique does not require expensive modernization of the flow path in hydraulic machines. Numerical simulations and experiments carried out by the authors suggest that surface treatment can considerably affect the cavitation processes, and the results of studies demonstrate the need for further in-depth investigation of cavitation processes in hydraulic machines, including with the use of modern application software tools. [ABSTRACT FROM AUTHOR]

This article deals with the numerical simulation of unsteady cavitating flow around hydrofoils, supported by experimental research realized in a cavitation tunnel situated in the Centre of Hydraulic Research. Two straight NACA hydrofoils (NACA0020 and NACA2412) were employed. The comprehensive unsteady CFD analysis was based on scale-resolving simulations (hereinafter SRS) with the aim of capturing correctly the interactions between the cavitation structures and re-entrant flow as well as the compressibility and thermal effects of cavitation. The static pressure fluctuations during the cavity oscillation cycles and the evaporation and condensation processes are discussed in detail. To predict correctly the high-pressure peaks during the bubble cloud collapses and the pressure pulse propagation speed, the real properties of water and the mixture total energy conservation equation were considered. In addition, the estimated content of undissolved air was taken into account. The numerical simulations were validated by means of already published experiments or compared with experiments conducted by the authors, and with good agreement.

Featured Application: Bulb water turbine blades with improved cavitation properties. The influence of a bulb runner blade hydrofoil shape on flow characteristics around the blade was studied. Experimental work was performed on a bulb turbine measuring station and a single hydrofoil in a cavitating tunnel. In the cavitation tunnel, flow visualization was performed on the hydrofoil's suction side. Cavitation structures were observed for several cavitation numbers. Cavitation was less intense on the modified hydrofoil than on the original hydrofoil, delaying the cavitation onset by several tenths in cavitation number. The results of the visualization in the cavitation tunnel show that modifying the existing hydrofoil design parameters played a key role in reducing the cavitation inception and development, as well as the size of the cavitation structures. A regression model was produced for cavitation cloud length. The results of the regression model show that cavitation length is dependent on Reynolds's number and the cavitation number. The coefficients of determination for both the existing and modified hydrofoils were reasonably high, with R2 values above 0.95. The results of the cavitation length regression model also confirm that the modified hydrofoil exhibits improved the cavitation properties. [ABSTRACT FROM AUTHOR]

One of the important things in a ship’s rudder design is the incidence angle of the rudder inflow to improve rudder cavitation performance. In the present study, the rudder inflow is measured by a 3-D LDV (laser Doppler velocimetry) system in a large cavitation tunnel, where the ship model tests are performed at a rather high Reynolds number of 107~108. Through the evaluation of the transverse velocity component using water injection experiments in the test section, the reliability of the 3-D LDV measurements is confirmed. The three-dimensional velocity components of rudder inflow between the rudder and propeller are successfully measured and are compared with numerical simulation results to see good agreement. The incidence angle distribution of the rudder inflow is obtained from the 3-D velocity components and shows a large angle at the range of 0.5 < Z/Span < 0.9, where the cavitation mainly occurred. The asymmetry-type rudder proposed based on rudder inflow measurements showed outstanding improvement of cavitation performance, compared with the flat-type rudder.

The article presents the numerical algorithm of the developed computer code which calculates performance characteristics of ducted axial-flow hydrokinetic turbines. The code makes use of the vortex lattice method (VLM), which has been developed and used in IMP PAN for years, to analyse the operation of various fluid-flow machines. To verify the developed software, a series of model tests have been performed in the cavitation tunnel being part of IMP PAN research equipment.

The application of surface-piercing propeller (SPP) has been widely used in high-speed crafts due to possessing many favorable features. Due to the information gaps in the design of SPP, researchers have made great efforts to conduct hydrodynamic analysis of these propulsion systems. Despite the previous studies, there is still a considerable shortage in literature. In this article, a comprehensive review has been carried out on the experimental, theoretical, and experimental–theoretical studies in the field of SPP to introduce the strengths, limitations, and gaps in the previous research. The results of previous studies have also been presented in the form of benchmarking tables and statistical figures. Investigations have proved the inability of the numerical methods to simulate SPP. In recent years, the most precise methods of analyzing complex flows around SPP have been the computational fluid dynamics methods. The most suitable computational fluid dynamics method is the Reynolds-averaged Navier–Stokes method. Moreover, despite the heavy costs of experiments, the experimental approach is still the most reliable way of understanding the flow phenomena, studying the time-dependent dynamic behavior of propellers, and determining the hydrodynamic coefficients of thrust and torque. It can also serve to develop the numerical methods for comparing the results and reducing the errors of semi-experimental equations. Therefore, one of the primary objectives of future studies will be the comprehensive experimental analysis of various propeller blade profiles considering the effect of the variations of the trailing edge angle and the effects of the parameters influencing SPP, especially the shaft inclination angle. [ABSTRACT FROM AUTHOR]

This study considers a blunt trailing-edged propeller operating both in a uniform and a nominal wake fields. Experiments are performed in the cavitation tunnel of Hyundai Maritime Research Institute. The effects of propeller rotation speed, tunnel flow speed, and blade sheet cavitation growth on the generation mechanism of the singing propeller are investigated. The cavitation, sound, and vibration characteristics related to the singing phenomena are measured by a hydrophone, amicrophone, an accelerometer, and a highspeed digital camera. The natural frequencies of propeller blades are predicted using a finite elementmethod and verified by both contact- and noncontact-type impacthammer tests in air and underwater conditions. The inflow speed and angle of attack for each section of the propeller blades are calculated using the Reynolds-averaged Navier-Stokes equation- based flow analysis. Using a detached eddy simulation, the vortex shedding patterns and their frequencies are calculated. The predicted vortex shedding frequencies are compared with the measured singing frequency and blade natural frequency for determination of consistency. Under cavitation-free regime, the vortex shedding frequencies are predicted for normalized blade radial positions of .8R and .9R. The computed values are close to the two blade natural frequencies and also consistent with the double singing phenomena in the cavitation tunnel test. For fully developed blade sheet cavitation condition, the vortex formation in the wake region is observed to be strongly influenced by the cavitation growth on the pressure side surface. Propeller singing is diminished with the continuous growth of cavitation and is finally locked-off. The significant variation of the flow-induced sound and vibration levels are also observed for the locked-in and the locked-off conditions. The singing occurrence location and frequency under uniform inflow condition are analyzed to investigate the generationmechanism of propeller singing. This study can be applied to the analysis of singing location and its frequency of a propeller operating in the hullwake, which changes the angle of attack according to the propeller rotation angle. [ABSTRACT FROM AUTHOR]

An end plate propeller (ENDP) shaped by a diffused endplate bent to the pressure side is proposed in the paper. The ENDP differs from a contracted and loaded tip (CLT) propeller, and possess remarkable performance in terms of cavitation, efficiency, vibration, and noise comparing with that of CLT and conventional propeller, particularly operating at inclined shaft condition. According to experiments conducted in the cavitation tunnel of National Taiwan Ocean University, it is observed that the diffused endplate can effectively restrain tip vortex cavitation, and eliminate tip-plate cavitation typically found on the outer surface of the tip-plate of a CLT propeller. The optimal diameter of the ENDP is smaller than that of a conventional propeller; thus, the ENDP is more suitable for ships with small stern space. Besides, the thrust of the ENDP is contributed much more from its pressure side, therefore, the cavitation on the back is reduced, and the efficiency is increased. Sea trials using a yacht with the ENDP were carried out and the results show that vibrations due to the sheet cavitation at blade-rate frequencies by the ENDP are significantly decreased in comparison with those of conventional propeller, and overall broad-band amplitude caused by the tip vortex cavitation by the ENDP at high frequencies are nearly disappeared. [ABSTRACT FROM AUTHOR]

In this paper, we investigated physical characteristics of an artificial supercavity generated behind an axisymmetric cavitator. Experiments for the same model were carried out at two different cavitation tunnels of the Chungnam National University and the University of Minnesota, and the results were compared and verified with each other. We measured pressures inside the cavity and observed the cavity formation by using a high-speed camera. Cavitation parameters were evaluated in considering blockage effects of the tunnel, and gravitational effects on supercavity dimensions were examined. Cavity dimensions corresponding to the unbounded cavitation number were compared. In addition, we investigated how artificial supercavitation develops according to the combination of injection positions and direction.

In this study, the numerical analysis of unsteady cavitating turbulent flow behind a two-dimensional wedge-shaped body is performed using the commercial program STAR-CCM+ as a part of a fundamental study on the control fin of supercavitating underwater vehicles. We explore the vortex structures in the near and far wake fields and investigate the effect of cavity growth on the periodic characteristics of wake flow (σ = 1.0 ~ 2.0). Pressure fluctuations above the wedge are converted to sound pressure levels in the frequency domain via the fast Fourier Transform. As a result, we confirm that the shedding frequency of the vortices behind the body is strongly affected by the development of cavitation. As the cavitation number decreases, the frequency of the vortex in the near wake region decreases, and the force accelerating the Karman vortex in the far wake region decreases. In addition, we clearly validate the wake flow characteristics of a two-dimensional wedge-shaped body by comparing our numerical results with the experimental results carried out at the Chungnam National University Cavitation Tunnel (CNU-CT) at three different cavitation numbers (σ = 1.3, 1.5, and 2.0). Observations using a high-speed camera and measurements of pressure fluctuation above the test model are carried out to demonstrate the wake flow characteristics. [ABSTRACT FROM AUTHOR]

Abstract The behavior of ventilated supercavities under continuous and discrete gust flows was tested in a medium-sized high-speed cavitation tunnel at the Korea Research Institute of Ships and Ocean Engineering. To investigate the influences of experimental facilities on supercavitation observations, the experimental results were compared with experiments at the Saint Anthony Falls Laboratory under similar flow conditions. We suggested a new threshold criterion at which the total cavity length is shortened, which predicts that the total cavity length shrinks when the vertical velocity of an incident flow reaches approximately 4.5% of the horizontal flow velocity. Additionally, we found that discrete gust flows resulted in changes in the cavity shape that were smaller than those in continuous gust flows. Highlights • The influence of incident gust flows on supercavity shapes is investigated experimentally. • Ripples on the supercavity surface are caused by vortices shed from the cavitator. • Supercavities shorten once the vertical flow velocity reaches 4.5% of the horizontal flow velocity. • Discrete gust flows have little effect on the cavity shape relative to continuous gusts. [ABSTRACT FROM AUTHOR]

The influence of a bulb runner blade hydrofoil shape on flow characteristics around the blade was studied. Experimental work was performed on a bulb turbine measuring station and a single hydrofoil in a cavitating tunnel. In the cavitation tunnel, flow visualization was performed on the hydrofoil’s suction side. Cavitation structures were observed for several cavitation numbers. Cavitation was less intense on the modified hydrofoil than on the original hydrofoil, delaying the cavitation onset by several tenths in cavitation number. The results of the visualization in the cavitation tunnel show that modifying the existing hydrofoil design parameters played a key role in reducing the cavitation inception and development, as well as the size of the cavitation structures. A regression model was produced for cavitation cloud length. The results of the regression model show that cavitation length is dependent on Reynolds’s number and the cavitation number. The coefficients of determination for both the existing and modified hydrofoils were reasonably high, with R2 values above 0.95. The results of the cavitation length regression model also confirm that the modified hydrofoil exhibits improved the cavitation properties.

The objective of the present study is to investigate, by means of velocimetric measurements, the flow field generated by a marine propeller running with inclined shaft. Measurements have been carried out on a scaled model of a propeller in the cavitation tunnel of UNIGE using Laser Doppler Velocimetry (LDV) and the acquired data have been post-processed applying the ensemble average technique. The propeller configuration includes shaft appendages as in a typical twin screw vessel configuration. The tests have been performed also without propeller, considering different velocities, in order to characterize the incoming flow field and analyse possible effects on propeller flow. The complete 3-D flow field has been measured considering four transverse sections at different longitudinal locations, from upstream to downstream of the propeller, focusing on the near field wake. A longitudinal plane containing the propeller shaft has been considered as well. A dedicated interpolation technique is presented to improve the spatial resolution of data and allow advanced analyses. Results allow analysing the main characteristics of the flow field, including the evolution of its main structures. The effects of non uniform inflow conditions caused by the oblique flow are analysed focusing on the dynamics of vortexes and in particular on the trajectories and strength of the vortexes. • Laser Doppler Velocimetry for a propeller working in inclined shaft with appendages. • Complete three dimensional flow field of the propeller has been characterized. • Results in terms of phase locked and average velocity fields are presented. • Detailed analysis on stream tube and tip vortex dynamics are presented. [ABSTRACT FROM AUTHOR]

For Super-Cavitating Underwater Vehicles (SCUV), the numerical analyses and experiments in a large cavitation tunnel are carried out at relatively large Reynolds numbers. The numerical results agree well with experiments and the drag coefficient of SCUV is rarely changed by the Reynolds number. As the cavitation number is decreased, the cavity occurs and grows, the cavitator drag decreases and the body drag is affected by the degree of covering the body with the cavity. The tunnel effects, i.e. the blockage and the friction pressure drop of the tunnel, on the drag and the cavitation of SCUV are examined from the numerical results in between the tunnel and unbounded flows. In the tunnel, a minimum cavitation number exists and the drag of SCUV appears larger than that in unbounded flow. When the super-cavity covers the entire body, the friction drag almost disappears and the total drag of SCUV can be regarded as the pressure drag of cavitator

In this study, the hydrodynamics and noise prediction of a five blade marine propeller were analyzed through numerical and experimental methods under variety operational conditions. The hydrodynamics of the propeller was studied and the characteristic curves were presented in both numerical and experimental methods. Inception and development of sheet cavitation conditions are obtained in both numerical and experimental methods. The cavitation was started and developed by either increasing the propeller rotational speed in constant pressure or decreasing pressure, while the velocity was kept constant. Good agreements are observed between numerical and experimental results, qualitatively and quantitatively. The noise of the propeller was analyzed through Computational fluid dynamics (CFD) method, based on the formulation of Ffowcs Williams and Hawkings (FW-H). Similarly, the experimental results collected from hydrophones were compared with numerical simulations. Finally, the effects of reflection in cavitation tunnel were obtained by considering overall sound pressure levels in numerical and experimental results.

In this study, the deformation of supercavity shapes due to tunnel-wall blockage effects was explored in the medium-sized high-speed cavitation tunnel at the Korea Research Institute of Ships and Ocean Engineering (KRISO). It was observed that maximum cavity diameter is affected less than cavity length by experimental conditions. We adopt a new convention for specifying the cavity dimensions; namely, the cavity diameter at the first peak on the lower cavity outline is defined as the maximum cavity diameter. This enables one to exclude the shape deformations caused by tunnel walls when extrapolating experimental cavity dimensions to the equivalent cavities that would occur in unbounded flows. [ABSTRACT FROM AUTHOR]

Ventilated cavity flow over a fixed height 3-D wall-mounted fence is experimentally investigated in a cavitation tunnel for a range of free-stream conditions. The impact of 3-D effects on cavity topology is examined, along with the dependence of the cavitation number and drag on the volumetric flow rate coefficient, fence height based Froude number and vapour pressure based cavitation number. Three different flow regimes are identified throughout the range of cavitation numbers for a particular free-stream condition. Generally, the cavity has a typical re-entrant jet closure the intensity of which is found to increase linearly with increasing Froude number. This increase in re-entrant jet intensity causes an increase in drag with Froude number for constant volumetric flow rate coefficient. At low Froude numbers the closure mechanism transitions from a single to a split re-entrant jet. The parameters used to characterize the cavity topology show a linear dependence on Froude number irrespective of the closure mode. The cavity topology and drag are found to be independent of vapour pressure based cavitation number. [ABSTRACT FROM AUTHOR]

High-lift rudder performance is studied on the basis of model test results with regard to the requirement of interim guidelines of International Maritime Organization for minimum propulsion power to maintain the manoeuvrability in adverse weather. Model tests of two types of high-lift rudder in flow behind highly loaded propeller in a cavitation tunnel have clarified their performance comparing with a conventional mariner rudder. The analysis of the test data presented here proposes a procedure to deduce the equivalent rudder areas to conventional rudders for estimating minimum propulsion power of ships equipped with high-lift rudders in adverse weather. The authors estimated the required minimum speed and the minimum propulsion power of ships equipped with the high lift rudders according to the interim guidelines using the equivalent rudder areas quantified by the model tests. The test data, the analysis method, and the estimates for the guidelines reveal how the high-lift rudders perform and contribute well to reduce the required minimum propulsion power. [ABSTRACT FROM AUTHOR]

Thermodynamic effect of cavitation is a favorable effect for pumps, in which cavity volume is suppressed and suction performance of the pump is improved. When evaporation occurs in low pressure region inside the pump, local temperature is decreased by the latent heat, the local saturated pressure decreases, then the cavity is suppressed. The thermodynamic effect is known to appear when the main stream temperature closes to critical temperature of the fluid. In order to clarify the basic characteristics of the thermodynamic effect of cavitation, high temperature and high pressure water tunnel is constructed, in which the free stream temperature can be increased to 140°C. In this study, by using high accuracy measuring technique of temperature inside a cavity, temperature distribution inside a supercavitation on a hydrofoil in a hot water at 80°C and the variation of temperature depression inside a supercavitation from room temperature water at 20°C to hot water at 80 °C are measured. And the temperature depression is predicted in more high temperature region by using theoretical prediction. Additionally, through comparison of cavity length between room temperature water and hot water, the thermodynamic effect in hot water is discussed.

When the object is traveling in the water at tremendously high speeds, the cavity forms and grows up at a fore part of the object called cavitator, and the object is eventually enveloped by vaporized water, supercavitation. As a result, the only part of the object in direct contact with the water is the cavitator, so skin-friction drag is significantly reduced. This is why recently supercavitating objects have been interested in many applicable fields. In this study we are focused out attention on supercavitating flows around various shapes of two and three dimensional cavitators. First, general features of supercavitation are examined by analyzing results obtained by the previously developed numerical method. Second, experimental observations are carried out at a cavitation tunnel at the Chungnam National University (CNU CT), and supercavity dimensions are scrutinized.

A pumpjet propulsor (PJP) was designed for an underwater body (UWB) with axi-symmetric configuration. Its performance was predicted through CFD study and models were manufactured. The propulsor design was evaluated for its propulsion characteristics through model tests conducted in a Wind Tunnel (WT). In the concluding part of the study, evaluation of the cavitation performance of the pumpjet was undertaken in a cavitation tunnel (CT). In order to assess the cavitation free operation speeds and depths of the body, cavitation tests of the PJP were carried out in behind condition to determine the inception cavitation numbers for rotor, stator and cowl. The model test results obtained were corrected for full scale Reynolds number and subsequently analyzed for cavitation inception speeds at different operating depths. From model tests it was also found that the cavitation inception of the rotor takes place on the tip face side at higher advance ratios and cavitation shifts towards the suction side as the RPS increases whereas the stator and cowl are free from cavitation.

Experimental investigations were carried out on an Axi-symmetric Body Model fitted with Pump-jet Propulsor (PJP) in the Cavitation Tunnel at Naval Science and Technological Laboratory (NSTL). The tests were intended for evaluating the propulsion characteristics of the body and propulsor. The self propulsion point of the model for two configurations was determined after finding the corrections for tunnel blockage effects and differences in model length at zero trim. The results were found to match closely with the towing tank results. The rotor and stator torques also matched closely over full range of experiment. Further experiments were carried out on the body at 4.5° angle of trim to investigate the propulsive performance and assess the operational difficulties in the sea. The results indicated an increase in resistance and decrease in rotor thrust; but the balance of torques between the rotor and stator was undisturbed, causing no concern to vehicle roll.

In present work, an acoustic characterisation of the University of Genoa cavitation tunnel is presented, with the aim to obtain suitable transfer functions in order to take into account (at least partially) the effects of the confined environment, particularly important for small-scale facility like the one considered. The acoustic characterisation is performed considering two hydrophones in significantly different positions (inside the tunnel and in an external tank), typical, for different reasons, of noise measurements in cavitation tunnel; the procedure is based on the logarithmic sine sweep signal. The obtained transfer functions have been applied to a series of measurements of model propellers in correspondence to considerably different functioning conditions, in terms of cavitation number and propeller loading, showing the applicability of the procedure and the improvement of the measurement quality, in view of predictions in full scale. [ABSTRACT FROM AUTHOR]

Today, passenger and racing boats increasingly utilize surface-piercing propellers. This type of propeller operates in two distinct phases of water and air simultaneously. As a result, this propeller type has additional characteristics that must be investigated separately from conventional propellers. A new family of surface piercing propellers was investigated using experimental and numerical methods. The family consisted of five propeller models with varying geometric features operating at an immersion ratio of 0.7. Experiments were conducted in the Sharif University of Technology's hydrodynamic group's cavitation tunnel. Additionally, using Star-CCM + software, the numerical simulation was performed using the RANS method for implicit unsteady flow with a sliding mesh technique in free surface conditions. The results indicate that by increasing the pitch ratio from 1.074 to 1.61, the critical advance coefficient value, which is in the range of 0.4–0.6, moves to 0.8–1 interval. Also, the efficiency enhances by 14% while raising the pitch ratio. The amplitude of force and moment fluctuation components increases at higher than 0.5 values of the advance coefficient by increasing pitch ratios. The expanded area grows proportional to an increased number of blades and as a result, the thrust and torque coefficients increase, but the efficiency does not improve significantly. Furthermore, the fluctuation amplitude of forces and moments applied to the key blade increases up to the critical advance coefficient in all models and then decreases for above critical values. [ABSTRACT FROM AUTHOR]

In this study, the hydrodynamics and noise prediction of a five blade marine propeller were analyzed through numerical and experimental methods under variety operational conditions. The hydrodynamics of the propeller was studied and the characteristic curves were presented in both numerical and experimental methods. Inception and development of sheet cavitation conditions are obtained in both numerical and experimental methods. The cavitation was started and developed by either increasing the propeller rotational speed in constant pressure or decreasing pressure, while the velocity was kept constant. Good agreements are observed between numerical and experimental results, qualitatively and quantitatively. The noise of the propeller was analyzed through Computational fluid dynamics (CFD) method, based on the formulation of Ffowcs Williams and Hawkings (FW-H). Similarly, the experimental results collected from hydrophones were compared with numerical simulations. Finally, the effects of reflection in cavitation tunnel were obtained by considering overall sound pressure levels in numerical and experimental results. [ABSTRACT FROM AUTHOR]

Normally, tip vortex cavitation (TVC) is first observed at a certain location behind the tips of propeller blades. Therefore, TVC is important for naval ships and research vessels that require raising the cavitation inception speed to maximum possible values. The concepts for alleviating the tip vortex are summarized by Platzer and Souders (1979), who carried out a thorough literature survey. Active control of TVC involves the injection of a polymer or water from the blade tip. The main effect of such mass injection (both water and polymer solutions) into the vortex core is an increase in the core radius, consequently delaying TVC inception. However, the location of the injection port needs to be selected with great care to ensure that the mass injection is effective in delaying TVC inception. In the present study, we propose a semiactive control scheme that is achieved by attaching a thread at the propeller tip. The main idea of a semiactive control is that because of its flexibility, the attached thread can be sucked into the low-pressure region closer to the vortex core center. An experimental study using a scale model was carried out in the cavitation tunnel at the Seoul National University. It was found that a flexible thread can effectively suppress the occurrence of TVC under the design condition for a model propeller. [ABSTRACT FROM AUTHOR]

Abstract: The Air-Cavity Ship (ACS) concept is currently being researched as one of the more promising concepts for economical forms of marine transportation. An Air-Cavity Ship uses an air injection system to isolate the bottom part of the ship's wetted surface from the water and thereby to reduce the frictional resistance. The air cavities are generated injecting air at the keel level of a vessel as such the cavities can extend along considerable portions of the hull bottom thus isolating it from the effect of the fluid. The main objective of an effective air cavity system is therefore to maximize the cavity length whilst minimising the air supply. Building on the lack of published experimental research, this paper presents a recent fundamental experimental investigation on air-cavities underneath a flat plane tested in the Emerson Cavitation Tunnel of Newcastle University. The experimental investigation uses this simplified model to understand the correlation of cavity length and volume with potential drag reduction due to the air cavity. The main objective of the research was to generate both fundamental and practical knowledge that furthered the understanding of the air-cavity phenomenon to help its potential application in practice. In addition an attempt was also made to correlate the findings from this experimental study with air-cavity theory and results from limited previous experimental studies performed in other facilities. [Copyright &y& Elsevier]

Abstract: This paper addresses the pressure fluctuation induced by a propeller sheet cavitation. This study applies the acoustic theory proposed by Ffowcs Williams and Hawkings to the prediction of the pressure fluctuation caused by the volume variations of the propeller cavitation. There are two objectives of this study. The first objective is to clarify and analyze the mechanism of the pressure fluctuation induced by the propeller sheet cavitation. The second objective is the evaluation of the developed numerical prediction method. Various factors that affect the pressure fluctuation are numerically simulated and analyzed based on the developed governing equation. The developed time domain prediction method is combined with the vortex lattice method, which solves for the unsteady sheet cavitation on the propeller blades. The numerical prediction results of the newly developed method are compared with the results of a potential-based numerical prediction method and the experimental results from the MOERI medium size cavitation tunnel tests for various operation conditions and propellers. As a result of this study, the pressure fluctuation induced by a propeller sheet cavitation is not simply proportional to the second derivative of the cavitation volume variation and inversely proportional to the distance. The fluctuation is represented by the combined result of the far-field term and the near-field term. Furthermore, various simulation results show that an elaborate prediction requires the overall consideration of the near-field term, the effect of the relative motion of the sources and the retarded time for the measurement position. The developed time domain prediction method provides reasonable results, and these results are in good agreement with the experimental results. In some cases, this method will provide much better results than the potential-based prediction method, especially for the prediction of the location where the maximum amplitude blade rate and the pressure amplitude of higher harmonics. [Copyright &y& Elsevier]

Numerical model of hybrid contra-rotating propeller (CRP) podded propulsion is built in numerical cavitation tunnel, and the hydrodynamics performance of hybrid CRP podded propulsion in uniform flow is predicted by RANS formula with SST k-w turbulence model based on sliding mesh method. The predicted results of open-water performance and unsteady performance of hybrid CRP podded propulsion are analyzed. Synchronously, a series of experimental investigations for open-water performance of hybrid CRP podded propulsion are carried out. Pod dynamical instrument and long-axis dynamical instrument are used in cavitation tunnel of the same size. The repeated tests' results are compared well with each other, indicating that the tests are stable. The average value of the repeated tests' results agree well with the prediction results of open-water performance. It is shown that the experimental method and the numerical method presented in this paper have good precision in the prediction of hybrid CRP podded propulsion's open-water performance. The average value of the repeated tests' results and predicted results are compared with the foreign experimental value of the same CRP without pod. The influence of pod on the open-water performance of the forward propeller and the after one are analyzed. It is shown that pod has no influence basically on open-water performance of the forward propeller, but has an obvious influence on the after one. [ABSTRACT FROM AUTHOR]

The objective of the present study is to investigate propeller wake using particle image velocimetry (PIV) technique with bubble type of tracers, naturally generated by the decrease in the static pressure in a cavitation tunnel. The bubble can be grown from the nuclei melted in the water tunnel and the size of bubbles is changed by varying the tunnel pressure. A series of experiments are conducted in the conditions of the uniform and high velocity gradient flows to find out the characteristics of bubble tracers and compared the measurement results using bubbles with those using solid particles. Bubbles showed good trace ability in the region of 15 S<75; however some discrepancies showed at high velocity gradient region of ReS ≈ 1000. The fitted vorticity reduction rate would give reference for the prediction in a real flow when bubble tracers are utilized in PIV measurements of a vortical flow. In addition, the characteristics of bubble slip velocity can provide information on the vortex core center and the reduction in the Reynolds shear stress caused by bubble's deformability. [ABSTRACT FROM AUTHOR]

One of the important things in a ship's rudder design is the incidence angle of the rudder inflow to improve rudder cavitation performance. In the present study, the rudder inflow is measured by a 3-D LDV (laser Doppler velocimetry) system in a large cavitation tunnel, where the ship model tests are performed at a rather high Reynolds number of 107~108. Through the evaluation of the transverse velocity component using water injection experiments in the test section, the reliability of the 3-D LDV measurements is confirmed. The three-dimensional velocity components of rudder inflow between the rudder and propeller are successfully measured and are compared with numerical simulation results to see good agreement. The incidence angle distribution of the rudder inflow is obtained from the 3-D velocity components and shows a large angle at the range of 0.5 < Z/Span < 0.9, where the cavitation mainly occurred. The asymmetry-type rudder proposed based on rudder inflow measurements showed outstanding improvement of cavitation performance, compared with the flat-type rudder. [ABSTRACT FROM AUTHOR]

A new cavitation erosion testing procedure in high-speed cavitation tunnel is presented. The method is based on surface-mounted obstacles on a plane-convex hydrofoil leading edge. This experimental set-up is able to accelerate the accumulation of damage on specimens located behind the obstacles and presents several advantages. Measurable cavitation erosion damage has been obtained for a thermal spray coating and a stainless steel 13.4 after 75 h of operation. The hydrodynamic operating conditions have been an inlet flow velocity of 35 m/s, a sigma value of 1 and an incidence angle of 3°. Final erosion results have been compared with similar data obtained with the vortex cavitation generator (VCG) and the vibratory apparatus as a continuation of a previous study, see [Wear 233–235 (1999) 65]. The cavitation induced vibration monitoring provides a way to explain the apparent discrepancy of the erosion data between the tests with the high-speed cavitation tunnel and the vibratory apparatus. [Copyright &y& Elsevier]

The primary objective of this paper is to present cavitation tunnel tests performed on an optimised shape-adaptive composite hydrofoil and compare the results to other composite hydrofoils. The optimised composite hydrofoil was designed based on prior literature and was manufactured using an optimised ply orientation schedule and a pre-twist. In the same experiment schedule a composite hydrofoil that has a ply orientation that is opposite to the optimised hydrofoil was also tested. In addition to the cavitation tunnel experiments, the paper also presents results predicted from FEA and CFD simulations for the optimised hydrofoil and compares the results from numerical methods to experiments. The results show that the optimised hydrofoil has an improved L/D ratio and a delayed stall phenomenon compared to other hydrofoils. Furthermore, due to the pre-twisted optimised geometry, the hydrofoil does not suffer from loss of lift at low angles of attack. The experimental results demonstrated the importance of characterising the performance of flexible shape-adaptive hydrofoils based on the actual velocity of the flow in addition to the conventional characterisation based on Reynold's number. Additional numerical simulations were performed to investigate the hydrofoils observed load dependant deformation behaviour. These results clearly show that for the same Reynold's number, the hydrofoil can have an appreciably different response if the flow velocity is different. • Cavitation tunnel experiments were performed on a shape-adaptive carbon fibre hydrofoil with an optimized layup and shape. • The shape-adaptive hydrofoil demonstrated a wider lift-to-drag ratio curve. • A similar approach can potentially be used to design composite propeller blades with wider efficiency curves. • The hydrofoil demonstrated a delayed onset of stall, with reduced vibrations at high flow speeds and incidence angles. • The shape-adaptive hydrofoil had a dependence to the flow speed beyond its dependence to Reynold's number. • Finite element analysis using 2-way FSI can be used obtain accurate predictions of a shape-adaptive hydrofoil. [ABSTRACT FROM AUTHOR]

In this paper, the hydrodynamic performance, cavitation inception, and acoustic performance of a 5-bladed B-series propeller are experimentally investigated in the Sharif University of Technology cavitation tunnel. For hydrodynamic performance, thrust, torque, and efficiency of the propeller model were measured in open water tests. In the cavitation study, in addition to blade cavitation, tip vortex cavitation was also observed, and the cavitation bucket diagram was extracted in different advance coefficients. Finally, for the acoustic analysis of the propeller, the emitted noise in the cavitation tunnel was recorded using two hydrophones according to the recommended procedures of the International Towed Tank Conference (ITTC). Accordingly, the effects of the propeller ambient pressure and cavitation number on the sound pressure level of the B-series propeller are determined. The results can be used to determine the effects of flow parameters on the hydrodynamic and acoustic characteristics of the propeller. Moreover, points of cavitation inception are obtained in all advance coefficients, and it will be possible to extract the proper operating depth without cavitation or lower cavitation. • The hydrodynamic coefficients of a normal-skew B-series 5-blade propeller with rake are investigated. • The comprehensive cavitation bucket diagram of the propeller is captured in tunnel. • The acoustic signals of the propeller along with TVC and sheet cavitation impacts are recorded in the tunnel. • The Effects of propeller RPM and tunnel pressure on acoustic performance of the propeller are evaluated experimentally. • The study enables accurate prediction of the low-noise and low-cavitation operational region of the propeller for designers. [ABSTRACT FROM AUTHOR]

Sound pressure distribution around a monotone sound source was measured inside a marine propeller cavitation tunnel and compared with the calculated result by a two-dimensional boundary element method. The measured sound pressure distribution showed some peaks due to the reflection effect of the tunnel test section boundary. As the frequency increased, the sound pressure distribution became more complicated, showing more peaks. The tunnel reverberant effect should be taken into account when the noise data measured in the tunnel are converted into full-scale values. In the boundary element method calculation, the boundary condition at the acrylic observation window of the tunnel was examined in detail. The calculated sound pressure distribution pattern in the tunnel transverse section agreed well with the measured distribution when a reasonable boundary condition was adopted. The boundary element method is an effective method for theoretically predicting the acoustic field inside the cavitation tunnel if the precise boundary condition is adopted. [ABSTRACT FROM AUTHOR]