Articulating Axial-Flow Turbomachinery Rotor Blade For Enabling Variable Speed Gas Turbine Engine

Current technology gas turbine engines are generally optimized to operate at nearly a fixed speed with fixed blade geometries for the design operating condition. When the operating condition of the engine changes, the flow incidence angles may not be optimum with the blade geometries resulting in reduced off-design performance. But, if we have the capability of articulating the pitch angle of axial-flow compressor/turbine blades in coordination with adjustable stator vanes, it can improve performance by maintaining flow incidence angles within the optimum range for given blade geometries at all operating conditions. Maintaining flow incidence angles within the optimum range can prevent the likelihood of flow separation in the blade passage and also reduce the thermal stresses developed due to aerothermal loads for variable speed gas turbine applications. This paper discusses a recent invention of adaptable articulating axial-flow compressor or turbine rotor blade that can significantly impact developing a high efficiency variable speed gas turbine for rotorcraft or ground vehicles that may need to operate optimally at different torque/speed conditions during various maneuvers. U.S. Army Research Laboratory has partnered with University of California San Diego and Iowa State University Collaborators to conduct high fidelity stator-rotor interaction analysis for evaluating the aerodynamic efficiency benefits of an articulating axial flow turbine blade concept. In addition, a design study for articulating turbine or compressor rotor blade using smart material based actuators using Shape Memory Alloy (SMA) has been carried out. Highly coupled fluid-structure interaction computational study of articulating turbine rotor and stator blades, together with a design concept of articulating axial-flow turbomachinery rotor blade using a smart material such as SMA is presented

Direct immersogeometric fluid flow analysis using B-rep CAD models

We present a new method for immersogeometric fluid flow analysis that directly uses the CAD boundary representation (B-rep) of a complex object and immerses it into a locally refined, non-boundary-fitted discretization of the fluid domain. The motivating applications include analyzing the flow over complex geometries, such as moving vehicles, where the detailed geometric features usually require time-consuming, labor-intensive geometry cleanup or mesh manipulation for generating the surrounding boundary-fitted fluid mesh. The proposed method avoids the challenges associated with such procedures. A new method to perform point membership classification of the background mesh quadrature points is also proposed. To faithfully capture the geometry in intersected elements, we implement an adaptive quadrature rule based on the recursive splitting of elements. Dirichlet boundary conditions in intersected elements are enforced weakly in the sense of Nitsche\u27s method. To assess the accuracy of the proposed method, we perform computations of the benchmark problem of flow over a sphere represented using B-rep. Quantities of interest such as drag coefficient are in good agreement with reference values reported in the literature. The results show that the density and distribution of the surface quadrature points are crucial for the weak enforcement of Dirichlet boundary conditions and for obtaining accurate flow solutions. Also, with sufficient levels of surface quadrature element refinement, the quadrature error near the trim curves becomes insignificant. Finally, we demonstrate the effectiveness of our immersogeometric method for high-fidelity industrial scale simulations by performing an aerodynamic analysis of an agricultural tractor directly represented using B-rep