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January 2012 www.sname.org/sname/mt were shown, there didn?t appear to be a great deal of agellation of the nger material, but that will certainly not be the case for all test conditions. When agellation is occur- ring, a strobe light may prove very useful for observing the phenomenon in slow motion.? According to Moore, the combination of large test section and high-speed ow capabil- ity enables testing at higher Reynolds numbers than is possible with any equivalent facility. ?Most specically, the ability to observe ow conditions for extended periods of time is unique, and extremely valuable to practicing naval architects and marine engineers.? Dr. Zalek, the project leader, says ?Our program goals are to devise and execute a large-scale, high Reynolds number SES bow seal uid-structure physical experiment, and obtain a better understanding of the seal?air-cushion? water interface fundamental physics through a parameter matrix of experimental conditions.? He adds that the testing will examine bow seal position, deformation and motion; bow seal forces; bow seal local hydrodynam- ics; and the air cushion free surface. ?We?re not trying to model an SES in its entirety, but capture the physics of a SES bow seal system. e data will be useful in the development of physics-based numerical models.? e experiments will evaluate two dif- ferent seal types?the nger seal (5 ngers), and a two-dimensional planing-type seal at two seal-depth immersions (0, 6, and 12 in.), at dierent cushion pressures (3, 6, and 12 in. WC) and stream speeds between 4 through 8 m/s. Two dierent types of seal material will be evaluated, 63 oz/yd2Nitrile/ Nylon and 7 oz/yd2Hypalon/Nylon. More science, less art Dave Foster is the LCC director. He leads a team of six full-time civil service employ- ees. Because of its size, Foster says the LCC enables testing with more delity. ?If you test in a smaller scale facility, you take on assumptions. With computational fluid dynamics, we want to minimize the amount of adjustments you make by art. e more science you get, the better.? The LCC has the advantage of being the largest water tunnel in the world, says Dr. Lawrence J. Doctors, a professor in the School of Mechanical and Manufacturing Engineering at the University of New South Wales in Australia. ?Its dimensions are su- ciently large so that the Reynolds number of the test models is close to that of the prototype vessel or component of the vessel. In the cur- rent case, we are testing a model of a section of a bow seal suitable for an SES or an air-cushion vehicle (ACV). e model would be approxi- mately half or quarter scale. is means that the viscous eects (dependent on the Reynolds number) are close to those on the prototype. A second advantage of its large size is that the instrumentation of the model is more straight- forward. Our current seal model is very heavily instrumented with more than 70 channels of data. It would be physically dicult to install so many sensors on a smaller model.? Doctors says the testing will explore resistance of an SES; modeling of bow seals; drag of SES with immersed seals; validation for Alion?s ?Sea Train? concept; and Umoe Mandal?s SES. ?Another important advantage of a water tunnel is that one can pressurize the ow to a preset value,? says Doctors. ?e pressurization is normally negative in that we wish to lower the ambient pressure. e pres- surization or depressurization is executed by pumping a small quantity of water into or out of the tunnel. is characteristic does not apply to our current tests with a free surface. However, it is vital for studies of cavitation. Cavitation is a phenomenon that degrades the performance of propellers, foils, and other high-speed marine components.? Adding a free surface e LCC is normally completely lled with water for testing. To conduct free surface testing, the LCC has been fitted with the previously mentioned gate, designed at the University of Michigan. ?e carefully shaped two-part ap ts into the top of the facility just after the contraction and just upstream of the test section,? says Doctors. ?e angle of the gate can be controlled via a hydraulic system to the required angle. In this way, a free sur- face springs from the lower, sharp, edge of the gate. e height of the free surface is altered by the appropriate setting of the gate angle.? According to Doctors, an important require- ment is that the free surface must be at and horizontal in the vicinity of the test apparatus. ?is has been found to be the case,? he says. ?I am involved in the current testing and am very keen to analyze the test results and com- pare them with my theoretical model of SES and ACV seals,? Doctors says. ?Dr. Steve Zalek and his doctoral student, Andrew Wiggins, and the rest of the Michigan team, have produced a remarkable piece of test apparatus.? ?e fact that the navy is in possession of the LCC places it in the unique and superior posi- tion of being able to research and develop the most advanced naval vessels,? says Doctors. ?e hydrodynamic community is indeed fortunate to have such a facility available for these and many other highly sophisticated experiments.? The research effort, entitled ?Surface- Eect-Ship Bow-Seal High-Reynolds Number Experiments,? is being funded by ONR to sup- port the development and design of the highly innovative sea-base connector T-Craft proto- type demonstrator. But, says Program Officer Kelly Cooper with the Sea Platforms and Weapons Division at ONR, the project has benets beyond T-Craft. ?The experimentation will help us better understand this critical aspect of surface eect ships and air cushion vehicles, and will vastly improve the computer modeling tools available to ship designers.? MTCaptain Edward Lundquist, USN (Retired), is a principal science writer for MCR Federal LLC of Arlington, Virginia. þÿ TThe Lþÿ C CCC facility is available for researchers to conduct testing on a space-available basis. þÿ TTo inquire about testing capabilities and schedule availability, contact the director, Dave þÿ FFoster at 301-227-1228, or by e?mail at code5100web.nswccd@navy.mil þÿ TThe LCC test section is tted with viewing windows to allow visual observations of the ow. 42_48_Lundquistfeature_SNAME_Jan12_P3.indd 4812/22/11 3:42 PM