Numerical, analytical, experimental study of fluid dynamic forces in seals

NASA/Lewis Research Center is sponsoring a program for providing computer codes for analyzing and designing turbomachinery seals for future aerospace and engine systems. The program is made up of three principal components: (1) the development of advanced three dimensional (3-D) computational fluid dynamics codes, (2) the production of simpler two dimensional (2-D) industrial codes, and (3) the development of a knowledge based system (KBS) that contains an expert system to assist in seal selection and design. The first task has been to concentrate on cylindrical geometries with straight, tapered, and stepped bores. Improvements have been made by adoption of a colocated grid formulation, incorporation of higher order, time accurate schemes for transient analysis and high order discretization schemes for spatial derivatives. This report describes the mathematical formulations and presents a variety of 2-D results, including labyrinth and brush seal flows. Extensions of 3-D are presently in progress

Development of a CFD Code for Analysis of Fluid Dynamic Forces in Seals

The aim is to develop a 3-D computational fluid dynamics (CFD) code for the analysis of fluid flow in cylindrical seals and evaluation of the dynamic forces on the seals. This code is expected to serve as a scientific tool for detailed flow analysis as well as a check for the accuracy of the 2D industrial codes. The features necessary in the CFD code are outlined. The initial focus was to develop or modify and implement new techniques and physical models. These include collocated grid formulation, rotating coordinate frames and moving grid formulation. Other advanced numerical techniques include higher order spatial and temporal differencing and an efficient linear equation solver. These techniques were implemented in a 2D flow solver for initial testing. Several benchmark test cases were computed using the 2D code, and the results of these were compared to analytical solutions or experimental data to check the accuracy. Tests presented here include planar wedge flow, flow due to an enclosed rotor, and flow in a 2D seal with a whirling rotor. Comparisons between numerical and experimental results for an annular seal and a 7-cavity labyrinth seal are also included

A 3D-CFD code for accurate prediction of fluid flows and fluid forces in seals

Current and future turbomachinery requires advanced seal configurations to control leakage, inhibit mixing of incompatible fluids and to control the rotodynamic response. In recognition of a deficiency in the existing predictive methodology for seals, a seven year effort was established in 1990 by NASA's Office of Aeronautics Exploration and Technology, under the Earth-to-Orbit Propulsion program, to develop validated Computational Fluid Dynamics (CFD) concepts, codes and analyses for seals. The effort will provide NASA and the U.S. Aerospace Industry with advanced CFD scientific codes and industrial codes for analyzing and designing turbomachinery seals. An advanced 3D CFD cylindrical seal code has been developed, incorporating state-of-the-art computational methodology for flow analysis in straight, tapered and stepped seals. Relevant computational features of the code include: stationary/rotating coordinates, cylindrical and general Body Fitted Coordinates (BFC) systems, high order differencing schemes, colocated variable arrangement, advanced turbulence models, incompressible/compressible flows, and moving grids. This paper presents the current status of code development, code demonstration for predicting rotordynamic coefficients, numerical parametric study of entrance loss coefficients for generic annular seals, and plans for code extensions to labyrinth, damping, and other seal configurations

Analysis of Coupled Seals, Secondary and Powerstream Flow Fields in Aircraft and Aerospace Turbomachines

Higher power, high efficiency gas turbine engines require optimization of the seals and secondary flow systems as well as their impact on the powerstream. This work focuses on two aspects: 1. To apply the present day CFD tools (SCISEAL) to different real-life secondary flow applications from different original equipment manufacturers (OEM s) to provide feedback data and 2. Develop a computational methodology for coupled time-accurate simulation of the powerstream and secondary flow with emphasis on the interaction between the disk-cavity and rim seals flows with the powerstream (SCISEAL-MS-TURBO). One OEM simulation was of the Allison Engine Company T-56 turbine drum cavities including conjugate heat transfer with good agreement with data and provided design feedback information. Another was the GE aspirating seal where the 3-D CFD simulations played a major role in analysis and modification of that seal configuration. The second major objective, development of a coupled flow simulation capability was achieved by using two codes MS-TURBO for the powerstream and SCISEAL for the secondary flows with an interface coupling algorithm. The coupled code was tested against data from three differed configurations: 1. bladeless-rotor-stator-cavity turbine test rig, 2. UTRC high pressure turbine test rig, and, 3. the NASA Low-Speed-Air Compressor rig (LSAC) with results and limitations discussed herein

Flows in Pinned Arrays Simulating Brush Seals

Flows through idealized pin arrays were investigated using an unstructured grid finite difference model and the simplified Ergun model to predict leakage flows and pressure drops in brush seals. The models are in good agreement in the laminar region with departures in the laminar-turbulent transition region defined by the simplified Ergun model. No local disturbances in the velocity or pressure fields, symptomatic of turbulence were found in the numerical results. The simplified model failed to predict the pressure drop of a 32-pin anisotropic array. Transitional and anisotropic behavior require

Experimental Visualization of Flows in Packed Beds of Spheres

The flow experiment consisted of an oil tunnel, 76 x 76 mm in cross-section, packed with lucite spheres. The index of refraction of the working fluid and the spheres were matched such that the physical spheres invisible to the eye and camera. By seeding the oil and illuminating the packed bed with planar laser light sheet, aligned in the direction of the bulk flow, the system fluid dynamics becomes visible and the 2-D projection was recorded at right angles to the bulk flow. The planar light sheet was traversed from one side of the tunnel to the other providing a simulated 3-D image of the entire flow field. The boundary interface between the working fluid and the sphere rendered the sphere black permitting visualization of the exact locations of the circular interfaces in both the axial and transverse directions with direct visualization of the complex interstitial spaces between the spheres within the bed. Flows were observed near the surfaces of a plane and set of spheres as well as minor circles that appear with great circles and not always uniformly ordered. In addition to visualizing a very complex flow field, it was observed that flow channeling in the direction of the bulk flow occurs between sets of adjacent spheres. Still photographs and video recordings illustrating the flow phenomena will be presented

Virtual and Experimental Visualization of Flows in Packed Beds of Spheres Simulating Porous Media Flows

A videotape presentation of flow in a packed bed of spheres is provided. The flow experiment consisted of three principal elements: (1) an oil tunnel 76.2 mm by 76.2 mm in cross section, (2) a packed bed of spheres in regular and irregular arrays, and (3) a flow characterization methodology, either (a) full flow field tracking (FFFT) or (b) computational fluid dynamic (CFD) simulation. The refraction indices of the oil and the test array of spheres were closely matched, and the flow was seeded with aluminum oxide particles. Planar laser light provided a two-dimensional projection of the flow field, and a traverse simulated a three-dimensional image of the entire flow field. Light focusing and reflection rendered the spheres black, permitting visualization of the planar circular interfaces in both the axial and transverse directions. Flows were observed near the wall-sphere interface and within the set of spheres. The CFD model required that a representative section of a packed bed be formed and gridded, enclosing and cutting six spheres so that symmetry conditions could be imposed at all cross-boundaries. Simulations had to be made with the flow direction at right angles to that used in the experiments, however, to take advantage of flow symmetry. Careful attention to detail was required for proper gridding. The flow field was three-dimensional and complex to describe, yet the most prominent finding was flow threads, as computed in the representative 'cube' of spheres with face symmetry and conclusively demonstrated experimentally herein. Random packing and bed voids tended to disrupt the laminar flow, creating vortices

Numerical Analysis of Intra-Cavity and Power-Stream Flow Interaction in Multiple Gas-Turbine Disk-Cavities

A numerical analysis methodology and solutions of the interaction between the power stream and multiply-connected multi-cavity sealed secondary flow fields are presented. Flow solutions for a multi-cavity experimental rig were computed and compared with experimental data of Daniels and Johnson. The flow solutions illustrate the complex coupling between the main-path and the cavity flows as well as outline the flow thread that exists throughout the subplatform multiple cavities and seals. The analysis also shows that the de-coupled solutions on single cavities is inadequate. The present results show trends similar to the T-700 engine data that suggests the changes in the CDP seal altered the flow fields throughout the engine and affected the engine performance

Linearized MFL Model for Embedded Flaw Detection in Rails

Numerical models simulating magnetic flux leakage (MFL) phenomenon in ferromagnetic materials are nonlinear in nature and hence require excessive computational effort. This paper describes an approach for developing an equivalent linear model (ELM) where the ferromagnetic region is appropriately partitioned into different domains with each domain being assigned a constant permeability value depending on the magnetization level and the flaw size. The nonlinear behavior of the multi-layered object is then modeled using a linearized MFL model. The model is first validated and then applied to the flaw detection problem in a rail geometry.</p

Applications of Hilbert Module Approach to Multivariable Operator Theory

A commuting $n$-tuple $(T_1, \ldots, T_n)$ of bounded linear operators on a Hilbert space \clh associate a Hilbert module $\mathcal{H}$ over $\mathbb{C}[z_1, \ldots, z_n]$ in the following sense: $$\mathbb{C}[z_1, \ldots, z_n] \times \mathcal{H} \rightarrow \mathcal{H}, \quad \quad (p, h) \mapsto p(T_1, \ldots, T_n)h,$$where $p \in \mathbb{C}[z_1, \ldots, z_n]$ and $h \in \mathcal{H}$. A companion survey provides an introduction to the theory of Hilbert modules and some (Hilbert) module point of view to multivariable operator theory. The purpose of this survey is to emphasize algebraic and geometric aspects of Hilbert module approach to operator theory and to survey several applications of the theory of Hilbert modules in multivariable operator theory. The topics which are studied include: generalized canonical models and Cowen-Douglas class, dilations and factorization of reproducing kernel Hilbert spaces, a class of simple submodules and quotient modules of the Hardy modules over polydisc, commutant lifting theorem, similarity and free Hilbert modules, left invertible multipliers, inner resolutions, essentially normal Hilbert modules, localizations of free resolutions and rigidity phenomenon. This article is a companion paper to "An Introduction to Hilbert Module Approach to Multivariable Operator Theory".Comment: 46 pages. This is a companion paper to arXiv:1308.6103. To appear in Handbook of Operator Theory, Springe