TAILIEUCHUNG - Theory Design Air Cushion Craft Episode 15

Tham khảo tài liệu 'theory design air cushion craft episode 15', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 546 Propulsion system design Fig. Variable area water jet inlets. Water-jet inlets can either be flush to the base-line of the SES hull or extended as a pod to capture flow from the area undisturbed by the hull boundary layer. Pod inlets are used on hydrofoils. The SES 100A test craft was originally fitted with pod inlets see Fig. . These comprised a main high-speed intake and auxiliary inlets allowing greater flow at lower speeds. Performance was less than projected and so the craft was retrofitted with variable area flush inlets. These initially had problems with air ingestion in a seaway and so various geometries of fence between the intakes and the sidehull lower chines were experimented with until performance was satisfactory. Further studies were then carried out on the variable geometry inlets which did not behave according to design predictions. It was found to be very difficult to set the ramp position for optimum thrust and at the same time avoid cavitation either internally or externally. Eventually it was found that a round fixed area inlet could give a reasonable compromise without the complexities of the variable ramp operating mechanism and so this design was selected for the 3KSES as a design basis. At craft speeds of 30 knots Fi Fc variation between and can occur without cavitation on a typical well-designed flush type inlet see Fig. . This range narrows to VJVC of at 70 knots and further to at around 100 knots. Below the lower boundary cavitation occurs under the rear intake lip while above the upper boundary flow separates from the intake roof or the inside of the lower lip. Water jets 547 It can be seen therefore that if a craft is designed for VJVC to be at 70 knots this will become at 30 knots and cavitation will occur on the inside of the inlet unless the pump flow is reduced to about 60 of design. This may be acceptable so long as the SES drag hump is not too high . for high LIB .

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