تحقيق پارامترهاي موثر در شبيه‌سازي عددي جريان غير كاويتاسيوني و كاويتاسيوني حول پروانه‌ي استاندارد 4119DTMB

Effective Parameter Investigation in Numerical Simulation of Cavitation and Non-Cavitation Flow around a DTMB 4119 Standard Propeller

در اين نوشتار جريان هاي غير كاويتاسيوني و كاويتاسيوني حول پروانه‌ي دريايي 4119DTMB با روش RANS سه‌بعدي حل شده است. ضرايب تراست، گشتاور و بازدهي نيز براي اين پروانه در هشت شبيه‌سازي استخراج و با نتايج تجربي مقايسه شد. الگوي كاويتاسيون مشخص شد و موقعيت و منطقه‌ي توسعه‌ي حفره نيز به دست آمد. به‌علاوه، تحقيقات عددي براي سه پارامتر مهم: ضريب پيشروي، عمق كاري پروانه و زبري سطح پروانه در جريان كاويتاسيوني انجام شد. مطالعه‌ي اثر ضريب پيشروي روي سطوح پروانه نشان داد كه با ضريب پيشروي كم‌تر، مقدار فاز بخار بيشتري مشاهده مي شود. با پايين بردن عمق كاري پروانه در شرايط آب آزاد (افزايش فشار هيدروستاتيك)، جابه‌جايي محدوده‌ي حفره، تغييرات حجم حفره در نزديكي لبه‌ي حمله، و كاهش قله‌ي منحني كسر حجمي فاز بخار مورد بررسي قرار گرفت. همچنين، افزايش ارتفاع زبري تا مقدار معيني، باعث كاهش مقدار كسر حجمي فاز بخار شد و پس از آن رشد كرد.

In this paper, cavitation and non-cavitation flows around a marine propeller, DTMB 4119, with the RANS method, the K- ? turbulence model, the Singhal transfer model and the mixed model, were solved. The velocity and pressure fields around the propeller surfaces were obtained using the equations of continuity, momentum and the K-? model of turbulence. The pressure coefficient for two sections of the propeller with experimental data (Jessup 1989) in non-cavitation flow, and three sections in cavitation flow with numerical data (Sun 2008), was validated. Thrust, torque and efficiency coefficients were extracted for this propeller in eight simulations and compared with experimental data. The cavitation pattern was specified and also the position and the cavity development area were obtained. Furthermore, numerical investigations for the three important parameters, such as: advance coefficient, propeller working depth and surface roughness of propeller in cavitation flow, were undertaken. An advanced coefficient effect study on the propeller surfaces showed that with less advance coefficient, more vapor phase value is observed. Also, cavity boundaries are extended. Between advance coefficient values of 0.833 and 0.7, cavity volume results are less than the advance coefficient values of 0.7 and 0.6. So, the cavity boundaries are significantly extended. By downing the propeller working depth under open water conditions (increasing hydrostatic pressure), cavity boundary movement, cavity volume variation and curve peak reduction of the vapor phase volume fraction were investigated. The cavity center was away from the leading edge and the probability of tip vortex cavitation was reduced. The sustainability of tip vortex cavitation is more than sheet cavitation, the casue of which is, first, tip vortex cavitation, and then, sheet cavitation of the leading edge. Investigation on propeller surface roughness showed that optimal roughness height could be found. A and B models showed less cavity volume than the smooth model, while the C model showed more cavity volume. When roughness height was increased, the vapor phase volume fraction was firstly reduced, the results of A and B models being nearly the same. As a result, increasing the roughness height to a specific value caused a decrease in the vapor phase volume fraction value, which afterwards grew.