• Journal of Mechanical Science and Technology
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• v.18 no.7
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• pp.1222-1235
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• 2004

This study examines the influence of geometry on the internal flow and macroscopic behavior of the spray in Diesel nozzles. For this investigation, two bi-orifice nozzles were employed: one cylindrical and one conical. The first step is to use a non-destructive characterization method which is based on the production of silicone moulds so that the precise internal geometry of the two nozzles can be measured. At this stage the nozzles have been characterized dimensionally and therefore the internal flow can be studied using CFD calculations. The results gained from this experiment make it possible also to ascertain the critical cavitation conditions. Once the critical cavitation conditions have been identified, the macroscopic parameters of the spray can be studied in both cavitating and non-cavitating conditions using a test rig pressurized with nitrogen and with the help of a image acquisition system and image processing software. Consequently, research can be carried out to determine the influence that cavitation has on macroscopic spray behavior. From the point of view of the spray macroscopic behavior, the main conclusion of the paper is that cavitation leads to an increment of the spray cone angle. On the other hand, from the point of view of the internal flow, the hole outlet velocity increases when cavitation appears. This phenomenon can be explained by the reduction in the cross section of the liquid phase in the outlet section of the hole.

• Journal of the Society of Naval Architects of Korea
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• v.58 no.6
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• pp.391-399
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• 2021

In order to investigate force and cavitation characteristics for the flat & twisted rudders in the Large Cavitation Tunnel (LCT), the rudder dynamometer was designed and manufactured. The measuring capacities of lift, drag and moment are ±1000 N, ±2000 N, and ±150 N-m, respectively. The present dynamometer uses the actuator with a harmonic drive to control the rudder angle without backlash. As the target ship is a military ship with twin shaft, each dynamometer was installed above the port & starboard rudders. After the installation of the model ship with all appendages, the model test composed of rudder force measurement and cavitation observation was conducted for the existing flat rudder & the designed twisted rudder. While the flat rudder showed the big difference of lift & moment between port & starboard, the twisted rudder presented a similar trend. The cavitation of the twisted rudder showed better characteristics than that of the flat rudder. Another set of model tests were conducted to investigate rudder performance by the change of the design propeller. There was little difference in rudder performance for the design propellers with slight geometric change. Through the model test, the characteristics of the flat & twisted rudders were grasped. On the basis of the present study, it is thought that the rudder with better performance would be developed.

• Journal of the Society of Naval Architects of Korea
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• v.60 no.1
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• pp.31-37
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• 2023

In the present study, a method of performing cavitation erosion test directly on the anodized surface of the rudder model is proposed, not applying ink or paint on its surface. An image processing technique is newly developed to quantitatively evaluate the erosion damages on the rudder model surface after erosion test. The preprocessing saturation image, image smoothing, adaptive hysteresis thresholding and eroded area detection algorithms are in the image processing program. The rudder cavitation erosion tests are conducted in the rudder deflection angle range of 0° to -4°, which is used to maintain a straight course at the highest speed of the targeted navy ship. In the case of the conventional flat-type full-spade rudder currently being used in the target ship, surface erosion can occur on the model rudder surface in the above rudder deflection angle range. The bubble type of cavitation occurs on rudder surface, which is estimated to be the main reason of erosion damage on the rudder surface.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.4
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• pp.391-397
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• 2010

Performance tests of a liquid-oxygen pump were carried out using liquid nitrogen (LN2) as a working fluid in a cryogenic turbopump test facility in Korea Aerospace Research Institute (KARI). The tests were performed at 30-55% of the design rotational speed, and the results were compared with those from a water test. The experimental results confirmed the similarity of the hydraulic performance, which allows the prediction of the pump performance at a design rotational speed of 20,000 rpm. The overall cavitation performance of the pump in the cryogenic environment was better than that in the water environment for all ranges of flow rates and rotational speeds. Critical cavitation number at the design flow rate was determined as 0.012 from the cryogenic test, and as 0.024 from the water test. The improved cavitation performance is due to the thermodynamic effect in cryogenic fluids.

• Journal of the Society of Naval Architects of Korea
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• v.56 no.2
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• pp.168-174
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• 2019

In order to investigate Propeller Open Water (POW) characteristics for the high-speed propeller in Large Cavitation Tunnel (LCT), the high-capacity inclined-shaft dynamometer was designed and manufactured. Its measuring capacities of thrust and torque are ${\pm}2200N$ and ${\pm}120N-m$, respectively. The driving motor is directly connected to the propeller shaft. Inclined angle of the propeller shaft can be adjusted up to ${\pm}10^{\circ}$. As the pressure inside LCT can be adjusted in the range of 0.1~3.0bar, we can carry out the POW test at high Reynolds number (above $1.0{\times}10^6$) without propeller cavitation and the cavitation test in uniform flow. After the new dynamometer setup in LCT, the Reynolds number variation test and propeller open-water test were conducted at the inclined angle of $0^{\circ}$ and $6^{\circ}$. The present POW results of the new dynamometer are compared with those of the existing high-capacity dynamometer in LCT and of the dynamometer in the towing-tank. Through systematic model tests and comparison with their results, the performance of the new inclined-shaft dynamometer was verified. It is thought the POW test for the high-speed propeller should be better conducted at high Reynolds number.

• Tribology and Lubricants
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• v.11 no.1
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• pp.58-65
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• 1995

When marine lubricating oil began to be emulsified and oxidized through ingressive water that have leaked from cooling pump seal systems, cooler, purifier system and piping system, the cavitation erosion-corrosion in alloy metals of bearings remains to the various troublesome problem at effective engine performance. Therefore, applied the cathodic protection to the control test of cavitation erosion-corrosion, and appointed the marine system oil containing 3% sea water as test environments, with different conductibility. Also, used the piezoelectric vibrator with 20 KHz, 24 $\mu$m as the cavity generation apparatus, and examined the weight loss, potential value, current density etc. in specimens with those condition. According to this testing data, investigated influence of cathodic protection on the control characteristics of cavitation erosion-corrosion, and will serve those as an elementary design data of marine bearing.

• Journal of the Society of Naval Architects of Korea
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• v.45 no.4
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• pp.370-378
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• 2008

It is reported to develop the driving pump for the Low Noise Large Cavitation Tunnel(LOCAT) which is under construction at Maritime & Ocean Engineering Research Institute(MOERI). For low background noise condition of the LOCAT, it is crucial not only the best pump efficiency but also no cavity occurrence at any operating conditions. Design condition of the pump is determined by considering the required pump headrise, flow quantity, shaft rotation velocity and pump diameter. Performance analysis of the pump is conducted using commercial CFD codes ($BladeGen^+$, CFX-10), and the predicted results are verified by a series of model tests. Cavity was not observed at any operating condition in the model test, which were conducted at the midium cavitation tunnel of MOERI. The optimum pump for LOCAT, named as LP-11, was successfully developed through a series of pump design processes composed of blade design, performance analysis and model test.

• Journal of the Society of Naval Architects of Korea
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• v.58 no.1
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• pp.10-16
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• 2021

This paper systematically investigates and correlates pressure fluctuation and nominal wake characteristics according to the angle of the vortex generators by introducing the angle adjustment method of the Vortex Generator (VG). The vortex generators are installed at the port and starboard of a model ship. The vortex generator performance test is executed on a model ship installed in the Large Cavitation Tunnel (LCT) and the angle of VG is freely controlled by a servo motor. The systematic test results for the vortex generator show that the well-designed VG is an effective appendage for reducing the pressure fluctuation level and shows the direction of VG's angular design optimization.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• v.y2005m4
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• pp.243-247
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• 2005

Hydraulic performance test was conducted for a fuel pump of a liquid rocket engine turbopump. The pump driven by an electric motor was tested in water environment. It is experimentally shown that the inducer had very small effect on the pimp's head and efficiency but great effect on the pump's cavitation performance. Additionally, inducer test was carried out to investigate the effect of the inducer on the pump in detail, and it was found that the pump had a critical cavitation number when the inducer head dropped by $55\%$.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.165-168
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• 2008

This study performed the 3-dimensional inspection analysis for cavitation by using the ultrasonic pulse velocity method to detect detailed various cavitations in a concrete test material. The internal-void are made of non-void test material and two types of which a regular square type and a rectangle type that produced through the 3-dimensional cavitation to put into a $500{\ast}500{\ast}500mm$ sized non-reinforced concrete test material. The tomography method for the ultrasonic pulse velocity method was used for the non-destructive test. As a result, this study has found that it is possible to visualize the cavitation as an image, and to analyze the internal-void in detail by the non-destructive method.