Integrated Aerodynamic And Hydrodynamic Optimization Of Amphibious Aircraft

The aerodynamic and hydrodynamic design of amphibious aircraftpresents unique challenge as the performance of cruise, water and landtake-off needs to be properly balanced. This paper developed an integratedframework using RANS-based hydrodynamic and aerodynamic analysismethods， coupled with response surface techniques. Both fuselage stepparameters and wing parameters are optimized with respects to watertake-off and cruise performance using the proposed framework.First, CFD hydrodynamic and aerodynamic calculations used in theframework are validated against experimental data. Wigley and F6modelare used in the validation. A decoupled hydrodynamic and aerodynamiccalculation procedure for amphibious aircraft water take-off process is thenintroduced. The results of the method meet the requirements ofengineering analysis. A more efficient drag breakdown method for thehydrodynamic drag calculation is incorporated into the framework. Themethod is based on hydrodynamic resistance theory. Computational time isreduced by around45%for the calculation of hydrodynamic drag in eachiteration for the take-off process compared to a full RANS method. By using different pressure viscous drag coefficients during the take-offprocess, the accuracy of the method can be improved.Fuselage step parameters are optimized using the proposedframework to minimize the water take-off distance. The longitudinallocation and depth of the fuselage step are the two parameters andoptimization objectives are water take-off distance and cruise lift-to-drag(L/D) ratio. Cruise L/D is calculated using RANS method at fixedincidence angle and water take-off distance is obtained through theproposed framework. L/D value drops monotonously with the increase intwo parameters, while minimum water take-off distance can be calculatedthrough this method.The linear relationships between the two fuselage step parameters andcruise performance for a given wing geometry allows the wing planform tobe optimized for cruise performance independent of optimization of stepfor take-off performance. Response surface method are combined with liftline theory and RANS calculations to optimize the wing planform andspanwise twist angle at cruise point. The topology of wing planform ismaintained the same throughout the process. Cruise lift-to-drag ratio andwing bending moment are the two objectives for fixed lift coefficient. Thewhole process is constructed in way that the wing twist angle is optimizedin an inner loop to produce the optimum span load distribution for eachspecific wing planform configuration, which is modified in an outer loopusing two separately built response surface models. The20DOE sample points used for building the response surfaces are evaluated using RANScalculations. Two objective Pareto Front is then produced based on the tworesponse surface models which are validated against additional samplepoints.In summary, the work introduced an efficient computationalframework for the aerodynamic design of amphibious aircraft consideringboth the water take-off and cruise performance. The aerodynamic andhydrodynamic calculations are decoupled with the hydrodynamic dragcalculated using a drag break-down approach. The method is applied to thefuselage step optimization and wing optimization of a typical amphibiousaircraft, providing an efficient engineering solution to the problem.