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Two approaches for CFD simulations for a complex geometry of a ship with an energy-saving duct are compared. One method is an unstructured grid method in which the single block grid can cover the whole geometry and the other is an overset grid method which uses multiple grid blocks for each component of the complex geometry. The computed results are compared with each other and with the experimental data for the resistance and the self-propulsion factors together with the flow fields. Based on these comparisons, two approaches are assessed from the practical point of view.

航空宇宙技術研究所 7-9 Jun. 1995 東京 日本, National Aerospace Laboratory 7-9 Jun. 1995 Tokyo Japan, 地面効果翼(WIG)機は次世代超高速船の有望な候補の1つとして期待されている。WIGは地面に近づくにつれて圧力中心が前方に移動し、揚抗比が大きくなる特徴を持っている。この特徴を正確に推定することは設計と安全性の評価の面で重要である。ここでは、翼端板を有する3次元翼周りの地面効果時の流れについて、Navier-Stokesソルバを用いて数値解析を行った。幾何学的形状が複雑なのでマルチブロック法を採用した。計算結果を実験データと比較し、地面効果における空力特性を討議した。, A WIG (Wing In Ground effect) vehicle is expected to be one of the promising super high-speed craft in the next generation. A WIG is characterized by a high lift to drag ratio and a forward shift of center of pressure in close proximity to the ground, hence estimating their features accurately is very important in design and safety evaluation. In the present investigation, flows around a three-dimensional wing with end-plates in ground effect are computed by a Navier-Stokes solver. Because of the geometric complexity of the configuration, a multi-block technique is used. Results are compared with experimental data and the aerodynamic characteristics in ground effect are discussed., 資料番号: AA0000294035, レポート番号: NAL SP-30

超高速船の最近の動きの中でPAR-WIG(Power Augmented Ram-Wing in round) が注目されている。PAR-WIGは、翼の下面に高いラム圧を生ずるよう翼の上流にスラスタを置いて揚力を増すようにした地面効果利用の翼である。PAR効果は船体が低い速度でも離着水できるようにし、在来型のWIGに比べ構造重量とエンジンパワーとが少なくてすむ。PAR-WIGの空力特性を理解するため非圧縮流れについての2次元ナビエ･ストークス方程式解法を開発した。解法は、有限容積法とfractional step法との組合せに基づいている。この解法を用いて、スラスト、翼下面の高ラム圧領域および空気力の間の関係を考察した。, In the recent trend of super high-speed ships, a Power Augmented Ram-Wing In Ground effect (PAR-WIG) has been paid attention to again. A PAR-WIG is a wing in ground effect, whose lift is enhanced by using the airflow of a thruster, which is placed in the upstream of the wing, so as to create a high ram pressure region under the wing. The PAR effect enables this vehicle to take off and land on at lower speed and supplies that structural weight and engine power can be reduced compared with the conventional WIGs. To understand the aerodynamic characteristics of a PAR-WIG, a two-dimensional Numerical Simulation (NS) solver for incompressible flow is developed. The solver is based on a finite-volume method whose algorithm is a fractional step method. Through the solver, relations among strength of thrust, high ram pressure region under the wing and aerodynamic forces are considered., 資料番号: AA0004174045, レポート番号: NAL SP-27

航空宇宙技術研究所 10-11 Jun. 1993 東京 日本, National Aerospace Laboratory 10-11 Jun. 1993 Tokyo Japan, 非圧縮性流れにつき、汎用マルチブロック計算法を用いてナビエ・ストークス方程式を解くプログラムを開発した。このソルバーを汎用マルチブロック格子形成法と組み合せることにより、流れ場を任意の寸法をもつ任意の数のブロックに分割して計算することができる。数値解法は、有限容積法とMUSCL(保存法則用単調性上流中心差分法)型3次精度の風上差分法とによる疑似圧縮性法である。シャフトブラケットのまわりの流れおよびより複雑な形状の物体のまわりの流れを計算することにより、ソルバーの妥当性を示した。, An NS (Navier-Stokes) solver for general purposed multiblock computation has been developed for incompressible flows. With the combination of a general purposed multiblock grid generator, it can compute flows made up of arbitrary number of blocks with arbitrary size. The based computational scheme is the pseudo compressibility method with the finite-volume discretization and the MUSCL-type (Monotonic Upstream centered Schemes for Conservation Laws) third-order upwing differencing. The validity of the solver was demonstrated by computing the flow around a shaft bracket, and the flow around a body with more complex geometry., 資料番号: AA0004171005, レポート番号: NAL SP-22

Validation and verification of a KCS model in head seas is presented in this paper for five wave conditions. Validation is performed by comparing added resistance, heave and pitch motions with experimental data. Numerical model is verified via grid refinement studies, assessing grid uncertainty for each test case. Periodic uncertainty by means of moving window FFT is introduced and assessed. The decomposition model is based on SWENSE (Spectral Wave Explicit Navier-Stokes Equations) method and implicit relaxation zones. Jump conditions at the interface are used to obtain interface-corrected interpolation schemes for density and pressure, embedding the free surface into two single-phase equations for water and air. The method fully resolves issues with parasitic air velocities and ensures one-cell-sharp jump of dynamic pressure and density across the free surface. Implicitly redistanced Level Set equation is used for interface capturing, while the k-omega SST model is used for turbulence. The method is implemented in the Naval Hydro pack based on foam-extend, a fork of the open source software OpenFOAM.

This paper presents detailed validation and verification study for the KCS in calm water conditions. Validation is performed by comparing the resistance, sinkage and trim with experimental data for six Froude numbers, while verification is performed for each case by assessing grid and iterative uncertainties. A single set of governing equations for water and air is used where jump conditions at the free surface are used to discretise discontinuous density and dynamic pressure fields. Volume of Fluid (VOF) method is used for interface capturing, and the k-omega SST model is used for turbulence modelling. Ship motion is solved with quaternion based six degrees-of-freedom (6 DOF) rigid body motion equations. The method is implemented in the Naval Hydro pack based on foam-extend, a community driven fork of OpenFOAM software.