详情

原文传递 Helicopter Rotor Safety Issues. Stage 1 Report. Revision B.

题名：	Helicopter Rotor Safety Issues. Stage 1 Report. Revision B.
作者：	Katz-A.; Grham-K.S.; Palmer-K.
关键词：	Rotary-wing-aircraft; Aviation-safety; Aerodynamics-; Computer-models.;Computational-fluid-dynamics; Equations-of-motion; Coning-; Flapping-; Rotor-moments; Wake-vortex.
摘要：	The University of Alabama has an ongoing effort in modeling of helicopter rotors and the study of rotor dynamics. The starting point of the present project was is the original true blade model, Bladehelo, previously developed at the University of Alabama Flight Dynamics Laboratory (UAFDL) and implemented in its real time simulator. Bladehelo employs rigorous equations of motion. It uses no prescribed motions and no small angle approximations. The project plan was to use Bladehelo, following certain upgrades, to assess the dynamic performance and the functional equivalence of composite blades to metal blades they replace, with a view to establishing certification requirements. The project is structured in three stages: Stage 1 consists of upgrades to Bladehelo. Stage 2 is concerned with validation of the upgraded model, and Stage 3 addresses the structural issues. The present report covers Stage 1 as carried out between 16 May 1998 and 15 May 2000.Two major modeling upgrades were implemented: flexible blades and a high fidelity wake. Flexible blades are modeled as articulated with adjacent segments joined by spring loaded hinges. Rather than model the segments and hinges specifically, a technique called structured modeling (SM) was invoked, which employs generic, model independent code, and allows the details of the model to be defined as input. SM, in turn, is based on the method of Global Recursive Dynamics (GRD). Both SM and GRD were developed at the UA FDL prior to the current project. In Stage 1, the pre-existing Bladehelo and SM codes were merged to create an upgraded Bladehelo, which was verified against the previous version and then applied to the modeling of flexible blades. The wake upgrade replaces the uniform inflow assumed in the pre-existing Bladehelo with a dynamic wake generated by a lattice of vortices created by the rotor blades. A trailing vortex is appropriate wherever the circulation about the blade changes, in our computational scheme, this occurs at both ends of each blade element. A shed vortex is appropriate whenever the circulation about the element changes, i.e. every integration step. The wake model creates and propagates the vortices in real time based on the flow field they generate. Limitations of computational throughput dictated that only tip and hub vortices be kept and that vortices be shed at a rate lower than the computational frame rate. Both upgrades required additional computational resources, especially the wake model. For thispurpose, the simulation host at the UA FDL was enhanced with four units of four processors each. The units are designated Monster0 through Monster3. The Monsters are interconnected bySCRAMNet. Multiprocessing proceeds in two stages, spreading to the four processors within each Monster and across the four monsters. Both stages were successfully implemented. Use ofthe 16 processors yielded a throughput improvement by a factor of 13.4. This allowed each ofthe upgrades mentioned above, as well as both of them together, to run in real time.
报告类型：	科技报告