We consider steady and time-dependent thermocapillary convection in encapsulated layers of moderate Prandtl number fluids. Assuming flat free surfaces and fluid/fluid interfaces, the two-dimensional, time-dependent Navier-Stokes equations and the energy equation are integrated by a time-accurate method on a stretched, staggered mesh. Particular attention is focused on the nature of time dependence in water encapsulation of Fluorinert FC-75 and in ethylene glycol encapsulated by FC-75 and hexadecane. We show that similar mechanisms for time-dependent thermocapillary convection exist for single-layer and multiple-layer fluid systems, and that shear effects at a thermocapillary interface can reduce convection in an encapsulated fluid layer. Based on our estimates for the thermal coefficients of interface tension, an apparent benefit of fluid encapsulation is to lessen the tendency toward time dependence. Nomenclature AR = aspect ratio Cp = specific heat at constant pressure k = thermal conductivity Lx, Ly = x and y dimensions of the cavity Ma = Marangoni number, crTATLx/iJLK Nu(x) = Nusselt number, Eq. (14) Pr = Prandtl number, V!K p =
This paper presents a computational aeroelastic study of a transonic transport wing using the Navier-Stokes equations for the fluid flow and modal equations for the structures. The computed results successfully predict pressure profiles, as well as the static deflections obtained in experiments. Unsteady calculations at M = 0.92 and a = 2 deg are presented, resulting in sustained aeroelastic oscillations as has been observed experimentally. The coupling and interaction of the shock oscillations and the modal response is observed using spectral analysis.
A computational study of natural convection of air in a tall rectangular cavity with 4 :1 aspect ratio is conducted. In an effort to investigate the applicability of the Boussinesq approximation to turbulent flow simulation, the cavity is differentially heated from the sides and is insulated at the ends at a Rayleigh number of 10 9 . Starting from quiescent and isothermal flow conditions, the flow is driven to turbulence without any artificial perturbations. The computer programme developed integrates the two-dimensional, time-dependent Navier-Stokes equations with the Boussinesq approximation and the energy equation by a time-accurate method on a stretched, staggered grid.
The latest improvements and results generated by ENSAERO-MPI are presented in this paper. ENSAERO-MPI is a parallelized, high-fidelity, multi-block code with fluids, structures and controls capabilities developed at NASA Ames Research Center under the support of HPCC. It is capable of multidisciplinary simulations by simultaneously integrating the Navier-Stokes equations, the finite element structural equations as well as control dynamics equations using aeroelastically adaptive, patched grids. Improvements have been made to the code's robustness, moving grid capabilities and performance.
An efficient procedure to compute aerodynamic influence coefficients (AIC) using high fidelity flow equations such as Euler/Navier- Stokes equations is presented. The AIC's are computed by perturbing structures using mode shapes. The procedure is developed on a multiple-instruction, multiple-data (MIMD) parallel computer. In addition to discipline parallelization and coarse-grain parallelization of the flow domain, embarrassingly parallel implementation of ENS AERO code demonstrates linear speedup for a large number of processors. Demonstration of the AIC computation for static aeroelasticity analysis is made on an arrow wing-body configuration. The computations show that some of the AIC's do not converge at the lower perturbation range since the perturbation is too small to prevail over the initial aerodynamic loads. The effect of initial aerodynamic loads disappears with increasing perturbation amplitude. The demonstrated linear scalability for multiple concurrent analyses shows that the threelevel parallelism in the code is well suited for the computation of the AIC's.
Multidisciplinary applications are suitable for parallel computing environment by adopting the domain decomposition method. Immediately, a multidisciplinary application can be parallelized by solving each discipline separately. In order to perform coupled multidisciplinary analysis, coupling of each discipline can be accomplished by exchanging boundary data at the interfaces. This is regarded as discipline-level parallelization. Next level could be a coarse-grain parallelization of each discipline, which mainly depends on the physical geometry and nature of each discipline. For example, it is almost impossible for structured-grid based computational fluid dynamics codes to do flow analysis of an aircraft by using a single grid because of the complexity of its configuration. Thus, multi-block grid is commonly used to describe the details of complex geometry. Similarly, in structural analysis, the structure is frequently subdivided into substructures. Thus, the computation of each subdomain can be easily parallelized since each subdomain is solved separately independent of other domains. The parallelization is accomplished by solving each subdomain separately on a separate processor and exchanging the boundary conditions at domain interfaces periodically. However, the physical decomposition of the domain introduces explicit boundary conditions at the domain interfaces. This is not desirable for critical areas such as those containing shock waves or flow separations. Thus, a fine-grain parallelization is introduced to overcome this problem. The fine-grain parallelization is one that solves exactly the same system of equations of a subdomain by using more than one processors without introducing any explicit boundary conditions. An efficient multidisciplinary analysis procedure can be accomplished by successfully combining the above multi-level parallelism. A multidisciplinary analysis code, ENSAERO developed at NASA Ames Research Center is used in this study to implement the proposed approach. The communication data structure required for the proposed approach will be studied in detail. This work will demonstrate the feasibility of using multi-level parallelization approach in multidisciplinary analysis applications.
Modem design requirements for an aircraft push current technologies used in the design process to their limit or sometimes require more advanced technologies to meet the requirement. New design requirements always demand to improve the operational performance. Accurate prediction of aerodynamic coefficients is essential to improve the performance. For example, in the design of an advanced subsonic civil transport, since the fluid flow at transonic regime shows strong nonlinearities, high fidelity equations, such as the Euler or Navier-Stokes equations predict flow characteristics more accurately than the linear aerodynamics, which are widely used in the current design process However, high fidelity flow equations are computationally expensive and require an order of magnitude longer time to obtain aerodynamic coefficients required in the design. Parallel computing is one possibility to cut down the computational turn-around time in using high fidelity equations so that high fidelity equations would be incorporated into the design process. By doing so, high fidelity equations would be used in the routine design process. This work will demonstrate the feasibility of using high fidelity flow equations in a design process by computing aerodynamic influence coefficients of a wing-body-empennage configuration on a multiple-instruction, multiple-data parallel computer.
