3555. A Fast Method For Estimating Airloads On Parts Of Aircraft At Arbitrary Flight Conditions To Support Early Mass Estimations
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Paper
Abstract
This paper presents a new CFD (Computational Fluid Dynamics) approach for nodal force evaluations at flight Mach numbers from low subsonic up to hypersonics. Airloads are an important input variable for flight mechanics which take into account the mass properties of aircraft. The simplest example is the aerodynamic vertical force necessary for lifting an aircraft at desired speed. With CFD, neutral point positions may be obtained for the Mach number range of the aircraft (three-axis static stability assessment). Mass properties do enter in unsteady phenomenons such as flutter, aero-structure-mass dynamics etc. Recent CFD developments aim at the analysis of flow details to perfection and thus require significant computer resources. In contrast to this approach the present work provides airload predictions by using fast computational methods with acceptable accuracy at less cost. The method is based on an integrated unstructured mesh generator equipped with an Euler- or optionally a Navier-Stokes solver. The mesh contains only bricks. It is body aligned with sublayers attached to the body surface for enhanced accuracy. The aircraft skin is user defined by scattered point coordinates. A newly developed 3D multilinear level set function is iteratively generated on a 3D cartesian mesh. This function produces cartesian cells having positive baricentric function values outside of the aircraft and negative values inside. In this way the discretized surface consists of quadrilaterals serving as boundary for the field mesh generator. An algorithm similar to the plate equation makes the aircraft surface smoothly pass through the input points. The solution of the Euler/Navier-Stokes equations is accelerated by a defect correction scheme invented by the author. Elementary numerical geometry is applied for distributing the forces on user defined structural nodes. Non-overlapping frames allow for partial conservative integration of the pressure distribution. The present CFD is suited for laptop usage.
