The increasing complexity of engineering systems has sparked increasing interest in multidisciplinary optimization (MDO). This paper presents a survey of recent publications in the field of aerospace where interest in MDO has been particularly intense. The two main challenges of MDO are computational expense and organizational complexity. Accordingly the survey is focused on various ways different researchers use to deal with these challenges. The survey is organized by a breakdown of MDO into its conceptual components. Accordingly, the survey includes sections on Mathematical Modeling, Design- oriented Analysis, Approximation Concepts, Optimization Procedures, System Sensitivity, and Human Interface. With the authors'' main expertise being in the structures area, the bulk of the references focus on the interaction of the structures discipline with other disciplines. In particular, two sections at the end focus on two such interactions that have recently been pursued with a particular vigor: Simultaneous Optimization of Structures and Aerodynamics, and Simultaneous Optimization of Structures Combined With Active Control.

/pdf/multidisciplinary-aerospace-design-optimization-survey-of-3xuwvr970l.pdf

Multidisciplinary Aerospace Design Optimization: Survey of Recent Developments

The primary focus of this paper is convective heat transfer in axial flow turbines. Research activity involving heat transfer generally separates into two related areas: predictions and measurements. The problems associated with predicting heat transfer are coupled with turbine aerodynamics because proper prediction of vane and blade surface-pressure distribution is essential for predicting the corresponding heat transfer distribution. The experimental community has advanced to the point where time-averaged and time-resolved three-dimensional heat transfer data for the vanes and blades are obtained routinely by those operating full-stage rotating turbines. However, there are relatively few CFD codes capable of generating three-dimensional predictions of the heat transfer distribution, and where these codes have been applied the results suggest that additional work is required. This paper outlines the progression of work done by the heat transfer community over the last several decades as both the measurements and the predictions have improved to current levels. To frame the problem properly, the paper reviews the influence of turbine aerodynamics on heat transfer predictions. This includes a discussion of time-resolved surface-pressure measurements with predictions and the data involved in forcing function measurements. The ability of existing two-dimensional and three-dimensional Navier-Stokes codes to predict the proper trends of the time-averaged and unsteady pressure field for full-stage rotating turbines is demonstrated. Most of the codes do a reasonably good job of predicting the surface-pressure data at vane and blade midspan, but not as well near the hub or the tip region for the blade. In addition, the ability of the codes to predict surface-pressure distribution is significantly better than the corresponding heat transfer distributions. Heat transfer codes are validated against measurements of one type or another. Sometimes the measurements are performed using full rotating rigs, and other times a much simpler geometry is used. In either case, it is important to review the measurement techniques currently used. Heat transfer predictions for engine turbines are very difficult because the boundary conditions are not well known. The conditions at the exit of the combustor are generally not well known and a section of this paper discusses that problem. The majority of the discussion is devoted to external heat transfer with and without cooling, turbulence effects, and internal cooling. As the design community increases the thrust-to-weight ratio and the turbine inlet temperature, there remain many turbine-related heat transfer issues. Included are film cooling modeling, definition of combustor exit conditions, understanding of blade tip distress, definition of hot streak migration, component fatigue, loss mechanisms in the low turbine, and many others. Several suggestions are given herein for research and development areas for which there is potentially high payoff to the industry with relatively small risk.

Convective Heat Transfer and Aerodynamics in Axial Flow Turbines

Mesures hydrodynamiques pour des jets dans un ecoulement transversal dans le cas du refroidissement par film des aubes de turbines a gaz

Hydrodynamic measurements of jets in crossflow for gas turbine film cooling application.

This paper presents the results of a detailed hydrodynamic study of a row of inclined jets issuing into a crossflow with a density ratio of injectant to freestream of two. Laser Doppler anemometry was used to measure the vertical and streamwise components of velocity for a jet-to-freestream mass flux ratio of 0.5. Mean velocity components and turbulent Reynolds normal and shear stress components were measured at locations in a vertical plane along the centerline of the jet from 1 diameter upstream to 30 diameters downstream of the jet. The results, which have application to film cooling, give a quantitative picture of the entire flow field, from the approaching flow upstream of the jet, through the interaction region of the jet and freestream, to the relaxation region downstream where the flow field approaches that of a standard turbulent boundary layer.Copyright © 1989 by ASME

Effects of density ratio on the hydrodynamics of film cooling

Advances in computational technology and in physics-based modeling are making large-scale, detailed simulations of complex systems possible within the design environment. For example, the integration of computing, communications, and aerodynamics has reduced the time required to analyze major propulsion system components from days and weeks to minutes and hours. This breakthrough has enabled the detailed simulation of major propulsion system components to become a routine part of designing systems, providing the designer with critical information about the components early in the design process. This paper describes the development of the numerical propulsion system simulation (NPSS), a modular and extensible framework for the integration of multicomponent and multidisciplinary analysis tools using geographically distributed resources such as computing platforms, data bases, and people. The analysis is currently focused on large-scale modeling of complete aircraft engines. This will provide the product developer with a "virtual wind tunnel" that will reduce the number of hardware builds and tests required during the development of advanced aerospace propulsion systems.

https://ntrs.nasa.gov/api/citations/20000063377/downloads/20000063377.pdf

The Numerical Propulsion System Simulation: An Overview

Axial flow turbine designers are currently using Navier-Stokes flow solvers to reveal the details of the three dimensional flowfield inside individual bladerow passages. This new capability has allowed designers to focus on secondary flow reduction to improve turbine efficiency. These steady bladerow solvers include viscous and film cooling effects and show good agreement with test measurements in the midspan region. However, the difference between computational results and data at the endwalls is significant due to the exclusion of endwall cavity effects. A clear understanding of how the flow entering and exiting the cavity interacts with the gaspath aerodynamics, in conjunction with an accurate computational model, are needed to predict accurately the secondary flow patterns and endwall losses. This investigation confirms that endwall cavity flows have a significant influence on gaspath aerodynamics and that they need to be included in bladerow computations for accurate results.Part I presents the experimental and computational results from an investigation of the endwall cavity and gaspath flow interaction in a low pressure turbine. Detailed test measurements were obtained in a low speed research turbine using state of the art geometry and served as a benchmark for the computational model. Hot wire and total pressure measurements were taken at multiple planes between bladerows to establish the interaction between the hub cavity and gaspath flows. Ethylene tracer gas was also applied to evaluate secondary flow characteristics of the stator and the migration of the cavity flow through the downstream rotor.Steady and unsteady computational analyses were utilized to model different combinations of the cavity and bladerow geometries. This building block approached allowed for separation of the flow physics involved in the interaction and identified the geometry and flow features that were critical to producing the best agreement with test data.In Part II, the development of a source term model for a steady bladerow solver that simulates endwall cavity flows in a low pressure turbine is reviewed. The source term model adequately captured endwall cavity effects and accurately predicted secondary flow in the adjacent bladerow. This source term model gives designers the capability to investigate new ideas of reducing secondary flow in a timely manner, leading to improvements in overall turbine efficiency.Copyright © 2000 by ASME

Endwall Cavity Flow Effects on Gaspath Aerodynamics in an Axial Flow Turbine: Part I — Experimental and Numerical Investigation

The recent trend in numerical modeling of turbine film cooling flows has been toward higher fidelity grids and more complex geometries. This trend has been enabled by the rapid increase in computing power available to researchers. However, the turbine design community requires fast turnaround time in its design computations, rendering these comprehensive simulations ineffective in the design cycle. The present study describes a methodology for implementing a volumetric source term distribution in a coarse grid calculation that can model the small-scale and three-dimensional effects present in turbine film cooling flows. This model could be implemented in turbine design codes or in multistage turbomachinery codes such as APNASA, where the computational grid size may be larger than the film hole size. Detailed computations of a single row of 35 deg round holes on a flat plate have been obtained for blowing ratios of 0.5, 0.8, and 1.0, and density ratios of 1.0 and 2.0 using a multiblock grid system to resolve the flows on both sides of the plate as well as inside the hole itself. These detailed flow fields were spatially averaged to generate a field of volumetric source terms for each conservative flow variable. Solutions were also obtained using three coarse grids having streamwise and spanwise grid spacings of 3d, 1d, and d/3. These coarse grid solutions used the integrated hole exit mass, momentum, energy, and turbulence quantities from the detailed solutions as volumetric source terms. It is shown that a uniform source term addition over a distance from the wall on the order of the hole diameter is able to predict adiabatic film effectiveness better than a near-wall source term model, while strictly enforcing correct values of integrated boundary layer quantities.

/pdf/coarse-grid-modeling-of-turbine-film-cooling-flows-using-28b31qjjhy.pdf

Coarse Grid Modeling of Turbine Film Cooling Flows Using Volumetric Source Terms

Axial flow turbine designers are currently using Navier-Stokes flow solvers to reveal the details of the three dimensional flowfield inside individual bladerow passages. This new capability has allowed designers to focus on secondary flow reduction to improve turbine efficiency. These steady bladerow solvers include viscous and film cooling effects and show good agreement with test measurements in the midspan region. However, the difference between computational results and experimental data at the endwalls is significant due to the exclusion of endwall cavity effects. A clear understanding of how the cavity flow interacts with the gaspath aerodynamics, in conjunction with an accurate computational model, is needed to predict accurately the secondary flow patterns and endwall losses.In Part I, the experimental and computational results from an investigation of the endwall cavity and gaspath flow interaction in a low pressure turbine were presented. Steady and unsteady computational analyses were utilized to model different combinations of the cavity and bladerow geometries. The data and computations confirmed that endwall cavity flows have a significant influence on gaspath aerodynamics and that these flows need to be included in bladerow computations for accurate results. However, the level of effort required to construct the computational grid and obtain a flow solution renders these computational models prohibitive.In Part II, the development of a source term model for a steady bladerow solver that simulates endwall cavity flows in a low pressure turbine is reviewed. Different levels of model complexity were evaluated to determine the impact of endwall geometry and source term distributions on analysis accuracy. The source term model adequately captured endwall cavity effects and accurately predicted secondary flow in the adjacent bladerow. This source term model gives designers the capability to investigate new ideas of reducing secondary flow in a timely manner, leading to improvements in overall turbine efficiency.© 2000 ASME

Endwall Cavity Flow Effects on Gaspath Aerodynamics in an Axial Flow Turbine: Part II — Source Term Model Development

The average passage approach has been used to analyze three multistage configurations of the GE90 turbine. These are a high pressure turbine rig, a low pressure turbine rig and a full turbine configuration comprising 18 blade rows of the GE90 engine at takeoff conditions. Cooling flows in the high pressure turbine have been simulated using source terms. This is the first time a dual-spool cooled turbine has been analyzed in 3D using a multistage approach. There is good agreement between the simulations and experimental results. Multistage and component interaction effects are also presented. The parallel efficiency of the code is excellent at 87.3% using 121 processors on an SGI Origin for the 18 blade row configuration. The accuracy and efficiency of the calculation now allow it to be effectively used in a design environment so that multistage effects can be accounted for in turbine design.

https://ntrs.nasa.gov/api/citations/19990095795/downloads/19990095795.pdf

Multistage Simulations of the GE90 Turbine

This paper describes our approach and experiences in constructing the Turbine Auto–Designer (TAD), an automated concurrent design system for aircraft engine turbines. In TAD, the design process is modeled based on the computer programs of a representative design system. It integrates three domains of the manual design process: preliminary design, detailed aerodynamic design, and detailed mechanical design.The manual design of turbines is an iterative redesign process involving the use of many sets of Computer Aided–Engineering (CAE) programs. The entire design process is modeled at four levels: analysis, automation, optimization, and concurrency. TAD is implemented with Engineous, a generic software shell for engineering design. Parts of TAD are already in use in day–to–day design practice for low–pressure turbines. In many cases of preliminary design, TAD can obtain better results quicker than the optimum obtained manually. Results also show that, for detailed aerodynamic analysis, the system can reduce the cycle time from days to hours.Copyright © 1993 by ASME

Scott D. Hunter

Papers

Endwall Cavity Flow Effects on Gaspath Aerodynamics in an Axial Flow Turbine: Part I — Experimental and Numerical Investigation

Coarse Grid Modeling of Turbine Film Cooling Flows Using Volumetric Source Terms

Endwall Cavity Flow Effects on Gaspath Aerodynamics in an Axial Flow Turbine: Part II — Source Term Model Development

Multistage Simulations of the GE90 Turbine

Toward Modeling the Concurrent Design of Aircraft Engine Turbines