Vorticity-transport and unstructured RANS investigation of rotor-fuselage interactions

The prediction capabilities of unstructured primitive-variable and vorticity-transport-based Navier-Stokes solvers have been compared for rotorcraft-fuselage interaction. Their accuracies have been assessed using the NASA Langley ROBIN series of experiments. Correlation of steady pressure on the isolated fuselage delineates the differences between the viscous and inviscid solvers. The influence of the individual blade passage, model supports, and viscous effects on the unsteady pressure loading has been studied. Smoke visualization from the ROBIN experiment has been used to determine the ability of the codes to predict the wake geometry. The two computational methods are observed to provide similar results within the context of their physical assumptions and simplifications in the test configuration

T-infinity: The Dependency Inversion Principle for Rapid and Sustainable Multidisciplinary Software Development

The CFD Vision 2030 Study recommends that, NASA should develop and maintain an integrated simulation and software development infrastructure to enable rapid CFD technology maturation.... [S]oftware standards and interfaces must be emphasized and supported whenever possible, and open source models for noncritical technology components should be adopted. The current paper presents an approach to an open source development architecture, named T-infinity, for accelerated research in CFD leveraging the Dependency Inversion Principle to realize plugins that communicate through collections of functions without exposing internal data structures. Steady state flow visualization, mesh adaptation, fluid-structure interaction, and overset domain capabilities are demonstrated through compositions of plugins via standardized abstract interfaces without the need for source code dependencies between disciplines. Plugins interact through abstract interfaces thereby avoiding N 2 direct code-to-code data structure coupling where N is the number of codes. This plugin architecture enhances sustainable development by controlling the interaction between components to limit software complexity growth. The use of T-infinity abstract interfaces enables multidisciplinary application developers to leverage legacy applications alongside newly-developed capabilities. While rein, a description of interface details is deferred until the are more thoroughly tested and can be closed to modification

CFD Simulations of Single- and Twin-Screw Machines with OpenFOAM

Over the last decade, Computational Fluid Dynamics (CFD) has been increasingly applied for the design and analysis of positive displacement machines employed in vapor compression and power generation applications. Particularly, single-screw and twin-screw machines have received attention from the researchers, leading to the development and application of increasingly efficient techniques for their numerical simulation. Modeling the operation of such machines including the dynamics of the compression (or expansion) process and the deforming working chambers is particularly challenging. The relative motion of the rotors and the variation of the gaps during machine operation are a few of the major numerical challenges towards the implementation of reliable CFD models. Moreover, evaluating the thermophysical properties of real gases represents an additional challenge to be addressed. Special care must be given to defining equation of states or generating tables and computing the thermodynamic properties. Among several CFD suite available, the open-source OpenFOAM tool OpenFOAM, is regarded as a reliable and accurate software for carrying out CFD analyses. In this paper, the dynamic meshing techniques available within the software as well as new libraries implemented for expanding the functionalities of the software are presented. The simulation of both a single-screw and a twin-screw machine is described and results are discussed. Specifically, for the single-screw expander case, the geometry will be released as open-access for the entire community. Besides, the real gas modeling possibilities implemented in the software will be described and the CoolProp thermophysical library integration will be presented

Deformable Overset Grid for Multibody Unsteady Flow Simulation

A deformable overset grid method is proposed to simulate the unsteady aerodynamic problems with multiple flexible moving bodies. This method uses an unstructured overset grid coupled with local mesh deformation to achieve both robustness and efficiency. The overset grid hierarchically organizes the subgrids into clusters and layers, allowing for overlapping/embedding of different type meshes, in which the mesh quality and resolution can be independently controlled. At each time step, mesh deformation is locally applied to the subgrids associated with deforming bodies by an improved Delaunay graph mapping method that uses a very coarse Delaunay mesh as the background graph. The graph is moved and deformed by the spring analogy method according to the specified motion, and then the computational meshes are relocated by a simple one-to-one mapping. An efficient implicit hole-cutting and intergrid boundary definition procedure is implemented fully automatically for both cell-centered and cell-vertex schemes based on the wall distance and an alternative digital tree data search algorithm. This method is successfully applied to several complex multibody unsteady aerodynamic simulations, and the results demonstrate the robustness and efficiency of the proposed method for complex unsteady flow problems, particularly for those involving simultaneous large relative motion and self-deformation

Computational Study of Microflaps with Application to Vibration Reduction in Helicopter Rotors

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90636/1/AIAA-55024-132.pd

Advances in Time-Domain Electromagnetic Simulation Capabilities Through the Use of Overset Grids and Massively Parallel Computing

A new methodology is presented for conducting numerical simulations of electromagnetic scattering and wave propagation phenomena. Technologies from several scientific disciplines, including computational fluid dynamics, computational electromagnetics, and parallel computing, are uniquely combined to form a simulation capability that is both versatile and practical. In the process of creating this capability, work is accomplished to conduct the first study designed to quantify the effects of domain decomposition on the performance of a class of explicit hyperbolic partial differential equations solvers; to develop a new method of partitioning computational domains comprised of overset grids; and to provide the first detailed assessment of the applicability of overset grids to the field of computational electromagnetics. Furthermore, the first Finite Volume Time Domain (FVTD) algorithm capable of utilizing overset grids on massively parallel computing platforms is developed and implemented. Results are presented for a number of scattering and wave propagation simulations conducted using this algorithm, including two spheres in close proximity and a finned missile

Feasibility Study of Slotted, Natural-Laminar-Flow Airfoils for High-Lift Applications

A computational fluid dynamics approach to evaluate the feasibility of a slotted, natural-laminar-flow airfoil designed for transonic applications, to perform as a high-lift system was developed. Reynolds-Averaged Navier-Stokes equations with a laminar-turbulent transition model for subsonic flow at representative flight conditions were used for this analysis. Baseline high-lift simulations were performed to understand the stall characteristics of the slotted, natural-laminar-flow airfoil. Maximum aerodynamic efficiency was observed with a constant slot-width. In addition, the effectiveness of the aft-element as a high-lift device was explored. Results indicate that a micro-flap is a viable option as a lift effector. These are most effective when combined with a Fowler-like motion. However, the maximum lift coefficient was limited, in part, by an early leading-edge stall largely due to the small nose radius required for supporting laminar flow. As a result, a drooped leading edge was added to the S207, the latest evolution of slotted, natural-laminar-flow airfoil technology. Morphing technology was also applied to mitigate abrupt wing-stall characteristics and further increase maximum lift. The use of morphing technology was observed to produce superior high-lift performance over hinged leading edge flap motions. However, off-body separation and narrow stall region in lift curves were observed for the S207\u27s high-lift system due to the aft-element position. The aft-element position was based on a previous study for the S204, a placeholder airfoil. Hence, an S207 aft-element optimized for high-lift was identified as the natural next step. A low-fidelity, slot-width sensitivity study was performed with the S207\u27s aft element in the form of a 9-point study. The focus of this study was to identify sensitivities of the slotted, natural-laminar-flow high-lift system to aft-element position variability. Three positioning boundaries were selected in reference to the stowed aft element and the gap between elements. Results show that the S207\u27s flap schedule should be dependent on the flap deflection angle and exit slot-width gap. Finally, a delayed-detached-eddy simulation was performed to improve confidence in the developed methodology. Strong agreement between RANS and DDES results was observed. These findings contribute novel knowledge to the state-of-the-art understanding of the revolutionary slotted, natural-laminar-flow airfoil technology

Numerical modelling of oscillating wave surge converters operating in array configurations

Ocean wave energy is becoming one of the most recognised renewable energy technologies due to its ability to deliver high-magnitude power. However, it has not yet achieved a stable position in the industry. Thus, research on these technologies is constantly growing to exploit wave energy efficiently. One step towards this goal is to deploy wave farms of single wave energy conversion systems, which brings additional hydrodynamic challenges decisive for its constructive operation. The Oscillating Wave Surge Converter (OWSC) is one of the most efficient technologies in operation due to its hydrodynamic behaviour and energy absorption capabilities. Models of OWSC arrays have been evaluated in the past using semi-analytical approaches resulting in little agreement on the most suitable layout. However, a comprehensive model to identify array configurations with constructive interaction on the most common operating sea states was not available. Moreover, a computational model accounting for nonlinear effects, including the influence of the Power Take-Off (PTO) and neighbouring devices, had not yet been developed. This study investigates the effects of sitting OWSCs in arrays through computational simulations, focusing on a comprehensive framework to calculate the power captured by three-OWSC arrangements with varying spacings and layouts. For this purpose, the Computational Fluid Dynamics (CFD) approach using overset mesh accounting for the large and independent motion of the devices is employed. Furthermore, the conditions covering the PTO representation using a reactive control strategy and the operational sea envelope are included in the model. The simulations carried out during this study successfully identified a set of spacings and layouts in which the arrays operate constructively. Within the key outcomes is that staggered arrangements perform more efficiently than in-line ones, increasing the power extracted by 30%. Furthermore, it is found that this is achieved through a strong interaction between the devices and the wave effects resulting from the energy extraction process

Fluid-structure interaction modeling on a 3D ray-strengthened caudal fin

In this paper, we present a numerical model capable of solving the fluid-structure interaction problems involved in the dynamics of skeleton-reinforced fish fins. In this model, the fluid dynamics is simulated by solving the Navier-Stokes equations using a finite-volume method based on an overset, multi-block structured grid system. The bony rays embedded in the fin are modeled as nonlinear Euler-Bernoulli beams. To demonstrate the capability of this model, we numerically investigate the effect of various ray stiffness distributions on the deformation and propulsion performance of a 3D caudal fin. Our numerical results show that with specific ray stiffness distributions, certain caudal fin deformation patterns observed in real fish (e.g. the cupping deformation) can be reproduced through passive structural deformations. Among the four different stiffness distributions (uniform, cupping, W-shape and heterocercal) considered here, we find that the cupping distribution requires the least power expenditure. The uniform distribution, on the other hand, performs the best in terms of thrust generation and efficiency. The uniform stiffness distribution, per se, also leads to 'cupping' deformation patterns with relatively smaller phase differences between various rays. The present model paves the way for future work on dynamics of skeleton-reinforced membranes