Newsletter EnginSoft Year 7 n°3 - 13

Aerodynamic and Acoustic Optimizationof Radial Fans

In this work the multiple objective optimization of radialfans with respect to aerodynamic efficiency and noisegeneration has been performed. This has been achieved bycoupling together an LSTM In-house Excel-VBA ImpellerDesign Tool (EVIDenT), the CAD program ProEngineer, thegrid generator ANSYS ICEM and the CFD solver ANSYS CFX, aswell as the LSTM In-house Acoustic Code SPySI (SoundPrediction by Surface Integration) within the optimizationsoftware modeFRONTIER®. From a technical point of view, thecoupling of the different tools was one of the mainchallenges solved with modeFRONTIER®. The input variablesfor the optimization were the shape parameter, i.e. the wrapangle of the impeller and its number of blades. Allsimulations have been performed in a 2D scenario in order tocapture primary fundamental aspects relevant to the impellerdesign. As a result of the optimization, the efficiency of theradial fans has been improved as well as the noise levelreduced substantially. A set of non-dominated solutions(Pareto solutions) have been obtained which can be usedaccording to the specific user requirements. The results showthat the integration of acoustics and transient flowsimulations within a multiple objective fully automatedoptimization process is feasible. Having established the fullyintegrated and automated process an extension also to 3Dcomputations can be readily performed.

IntroductionThe aim of this work is to analyze the possibility ofoptimization with modeFRONTIER® [1] byintegration of In-house and commercial tools inorder to automate turbomachinery design withrespect to efficiency and noise generation.The starting step in the optimization process isthe design of impellers with the In-house Excel-VBA Impeller Design Tool (EVIDenT), whichdelivers high performance starting blade shapesfor the fully integrated optimization process. Themain optimization parameters in this work werethe wrap angle, Figure 1, and the number ofblades. Many other parameters can be included,e.g. the blade inlet and outlet angles, shroudshape, but the scope of this work was toestablish the optimization work flow. Even so,with those two parameters already very goodresults were achieved. These geometries are thenexported into the CAD program ProEngineerwhere the impeller, e.g. Figure 1, and thecorresponding flow domains are generated.These geometries are then fully automatically

exported to the grid generator ANSYS ICEM where anotherscript generates also automatically the grids, Figure 2. Thegrid is exported to CFX, the flow domain is automatically setup, Figure 4, and the solver starts to run to compute the CFDsolution.

The results of the CFD simulation before and after theoptimization are shown in the stream line plots of Figure 3.One can clearly see that in the optimized design the flowvelocities in the impeller where reduced keeping, however,the same pressure and flow rate, as well as reducing

Fig. 1 - In-house Excel-VBA Impeller Design Tool (EVIDenT)

Fig. 2 - Wrap angle Fig. 3 - Radial impeller

Fig. 4 - Grid and fluid domain solver setup in ANSYS CFX Pre.

14 - Newsletter EnginSoft Year 7 n°3

substantially the sound pressure level. InFigure 4 three prototypes are shown.

The modeFRONTIER® optimizationenvironmentAs described above, the work flow was carriedout by integrating and automating with scriptsa set of commercial (ProEngineer [2], ANSYSICEM [3] and ANSYS CFX [4]) and In-housetools (Python based acoustic tool SPySI [5] andInhouse Microsoft Excel-VBA Impeller DesignTool EVIDenT [6]). But how to integrate allthese commercial and In-house tools in orderto perform a multi-objective optimization? Theanswer was to use modeFRONTIER®. The multi-objective optimization environment tool

modeFRONTIER® offers all features needed inorder to integrate the automation processes ofthe different programs and to perform powerfuloptimizations.

Multi-objective optimizationIn this case, as there were 2 objectives, a multi-objective algorithm had to be chosen. Thereforethe MOGA II algorithm was selected with 5generations and combined with a DOE Sobol of 8designs.

The work flow in modeFRONTIER® is shown in Figure 8. Herethe different tools and scripts used are integrated [6] usingthe modeFRONTIER® workflow connectors. The input variablenodes are used for the optimization inputs (e.g. number ofblades and shape parameter). These are then connected tothe first node (1), the In-house Excel-VBA Impeller DesignTool (EVIDenT) through the scheduler (8), shown in Figure 8.This design tool EVIDenT generates the information aboutthe number of blades and the data for the shape of the bladesand writes them out as text files. These files are then passedto the python node (2), which passes the variables in thescript to the CAD program ProEngineer (3). ProEngineer thencreates the flow domain for the blades as a parasolid file,which is then transferred to the ICEM node (4). To this node(4) also the ICEM script and the parasolid files for the otherparts of the geometry are transferred. Here in node (4) thenthe mesh is created and transferred as a CFX5 file to the CFXnode (5). In this node (5) some additional CFX5 files andscripts for pre and post processing arrive also from thetransfer and support file nodes. Node (5) runs thensimulation, calculates the efficiency and writes out the resultas a text file. From the CFX node (5) CSV (Comma separatedValue) files are transferred to the next tool in node (5),which consist of the acoustic In-house tool SPySI. It runs theSPySI tool and writes out the results, i.e. the sound pressurelevel, as text file. These files are then transferred to theoutput nodes (6), which are then finally transferred to design

Fig. 5 - CFD analysis of non optimized (left) and optimized impeller (right)

Fig. 6 - Sound pressure level of non optimized (left) and optimized (right)impeller

Fig. 7 - Prototypes

Fig. 8 - Work flow of the optimization process

Newsletter EnginSoft Year 7 n°3 - 15

objective nodes (7). These nodes make sure that efficiency ismaximized and the noise level is minimized. Based on thisinformation, the scheduler node (8) analyzes and generatesa new design.

Results obtained with modeFRONTIER®In this work a total of 96 possible designs were run, out ofwhich 35 designs were evaluated. From those the final threeoptimized designs were selected and compared with thethree original starting designs.

A set of non-dominated solutions, as shown in Figure 9, havebeen found which showed substantial improvements in theefficiency and reduction in the noise level. In the case of amulti-objective optimization, there is no single best designbut rather a set of non-dominated designs. The best designwith respect to efficiency has an increase of 35%, while thebest design with respect to noise level has a reduction of 3dB as compared to the original design, which means areduction of 50% in the sound power level

ConclusionsThis work has shown, Figure 8, how it is possible to integrateand automate different codes, i.e. the In-house ExcelEVIDenT code, ProEngineer, ANSYS ICEM, ANSYS CFX and theIn-house Acoustic tool SPySI in modeFRONTIER® and finallyhow to establish and carry out an multi-objectiveoptimization in this environment

The efficiency of radial fans has been improved as well as thenoise level reduced noticeably. A set of non-dominatedsolutions (Pareto solutions) have been obtained which canbe used according to the user needs.

References[1] modeFRONTIER®: http://www.esteco.com/products.jsp[2] Pro/Engineer Wildfire:

http://ptc.com/products/proengineer/[3] ANSYS ICEM CFD:

http://www.ansys.com/products/icemcfd.asp[4] ANSYS CFX:

http://www.ansys.com/products/fluid-dynamics/cfx/

[5] Scheit, C., Karic, B., Delgado, A., Epple, P. and Becker, S.(2009) Experimental and Computational Study of RadialImpellers With Respect to Efficiency and NoiseProduction. Conference on Modeling Fluid Flow (CMFF’09)The 14th International Conference on Fluid FlowTechnologies Budapest, Hungary, September 9-12.

[6] Masood, Rao M. A. (2010) Principle Study of Optimizationof Radial Fans with respect to Aerodynamics andAeroacoustics, Master Thesis, LSTM, University ofErlangen-Nürnberg.

Institute of Fluid Mechanics - Technical FacultyFriedrich-Alexander - University Erlangen-Nürnberg

MSc. Engr. Rao Muhammad Atif MasoodM.Sc Christoph ScheitDr.-Ing. Philipp Epple

Prof. Dr. A. Delgado - Professor and Head

Fig. 9 - The Pareto Front

The Institute of Fluid Mechanics (Lehrstuhl fürStrömungsmechanik - LSTM) of the Friedrich-Alexander-Universität Erlangen-Nürnberg has 8 departments workingon a large variety of research topics: Aerodynamics,Turbulence, Aeroacoustics, chemical reacting flows, fluidflow process automatization, bio and medical technology,numerical flow simulation, process fluid dynamics andTurbomachinery, instationary fluid mechanics, Engineeringof Advanced Materials and thermo-fluid-dynamics of bio te-chnological processes. There are about 70 researchers wor-king at the LSTM.The LSTM has many years of experience in the design, nume-rical computation and aerodynamic and acoustic optimiza-tion of turbomachines of all kinds – axial, diagonal and ra-dial. The aerodynamic design and acoustic computation aredone with Inhouse-codes as well as with commercial tools.www.lstm.uni-erlangen.de

Der Lehrstuhl für Strömungsmechanik (LSTM) der Friedrich-Alexander-Universität Erlangen-Nürnberg setzt sich aus 8Forschungsbereichen mit einer sehr breit angelegten themati-schen Ausrichtung zusammen: Aerodynamik, Turbulenz undAeroakustik, Strömungen mit chemischen Reaktionen,Prozessautomatisierung von Strömungen in Bio- undMedizintechnik, Numerische Strömungsmechanik,Prozessfluiddynamik und Strömungsmaschinen, InstationäreStrömungsmechanik, Engineering of Advanced Materials undThermofluiddynamik biotechnischer Prozesse. Insgesamt ar-beiten und forschen hier ca. 70 Mitarbeiter undMitarbeiterinnen.Der LSTM besitzt langjährige Erfahrung in der Auslegung, nu-merischen Berechnung und strömungsmechanischen und aku-stische Optimierung von Turbomaschinen aller Bauformen (ra-dial, diagonal und axial). Die strömungsmechanischeAuslegung und akustische Berechnung erfolgen sowohl mitInhouse-Codes wie auch über kommerziellen Tools.