RIBLET APPLICATION IN COMPRESSORS: TOWARDS EFFICIENT BLADE DESIGN?

Nowadays, modern axial compressors have already reached a very high level of development. The current study is focused on the question, if the application of riblets on the surfaces of a highly efficient modern compressor blade can be a further step towards more efficient blade design. Therefore, a highly loaded compressor cascade has been designed and optimized specifically for low Reynolds number conditions, as encountered at high altitudes and under consideration of the application of riblets. The optimization was performed at a Mach number of 0.6 and a Reynolds number of 1.5×105. Two objective functions were used. The aim of the first objective function was to minimize the cascade losses at the design point and at incidence angles of +5 and −5 degrees. The intention of the second objective function was to achieve a smooth distribution of the skin friction coefficient on the suction side of the blade by influencing the blade curvature in order to apply riblets. The MISES flow solver as well as the DLR optimizer “AutoOpti” were used for the optimization process. The developed compressor cascade was investigated in the transonic cascade wind tunnel of DLR in Cologne, where the Reynolds number was varied in the range of 1.5×105 to 9.0×105. Furthermore, the measurements were carried out at a low turbulence level of 0.8 percent and at a high turbulence level of 4 percent, representative for high pressure compressor stages. The measurement program was divided into two parts. The first part consisted of the investigation of the reference cascade. In the second part of the study riblets were applied on suction and pressure side of the cascade blades; two different manufacturing techniques, a rolling and a coating technique were applied. The rolling technique provides riblets with a width of 70 μm and the coated riblets have a width of 50 μm. The wake measurements were performed using a 3-hole probe at midspan of the cascade in order to determine the resulting losses of the reference blade and the blades with applied riblets. The detailed analysis of the measurements shows, that the riblets have only a slight influence on the viscous losses in the case of the compressor application in this study. Finally, these results are discussed and assessed against the background of feasibility and effort of riblet applications within the industrial design and manufacturing process

Wear protection of deep drawing tools by systematic optimization of highly stressed surfaces

The automotive sector is one of the largest energy consumers in Germany. Requests from politics and industry to significantly reduce emissions require new developments during utilization as well as during production phase. In line with the framework concept "InnoCaT", where more than 60 companies and research facilities from Germany take part, possibilities for producing companies are developed and analyzed to reduce the resource and energy consumption and by this reducing costs along the entire process chain of car body manufacturing. One approach to design car bodies lighter and more efficiently is to use aluminium and high strength steels. By this means weight and sheet thickness are reduced. However higher strengths of the steels and the adhesion affinity of aluminium significantly increase the requirements regarding the used tool steel. Thus grooves or galling appear more frequent at highly stressed surfaces. To assure high lifetimes and by this increase especially the resource efficiency concerning use of material and setting-up times within the press plant, a local optimization at the highly stressed surfaces is necessary. For this a FEM/BEM-tool for a time efficient and exact calculation of the occurring tool loads for complex die profiles is developed. Based on this development of load calculation a shape-optimization is performed at the corresponding areas. After the geometric optimization of the tool a local laser surface treatment for further wear protection is carried out using laser cladding or laser alloying/ -dispersing. By combining the technologies a highly wear resistant surface is achievable, which increases the tool's lifetime as well as the reproducibility within production

Riblet Application in Compressors: Toward Efficient Blade Design

Nowadays, modern axial compressors have already reached a very high level of development. The current study is focused on the question, if the application of riblets on the surfaces of a highly efficient modern compressor blade can be a further step toward more efficient blade design. Therefore, a highly loaded compressor cascade has been designed and optimized specifically for low Reynolds number (LRN) conditions, as encountered at high altitudes and under consideration of the application of riblets. The optimization was performed at a Mach number of 0.6 and a Reynolds number of 1.5 × 105. Two objective functions were used. The aim of the first objective function was to minimize the cascade losses at the design point and at incidence angles of +5 and −5 deg. The intention of the second objective function was to achieve a smooth distribution of the skin friction coefficient on the suction side of the blade by influencing the blade curvature in order to apply riblets. The MISES flow solver as well as the DLR optimizer “AutoOpti” was used for the optimization process. The developed compressor cascade was investigated in the transonic cascade wind tunnel of DLR in Cologne, where the Reynolds number was varied in the range of 1.5 × 105–9.0 × 105. Furthermore, the measurements were carried out at a low turbulence level of 0.8% and at a high turbulence level of 4%, representative for high pressure compressor stages. The measurement program was divided into two parts. The first part consisted of the investigation of the reference cascade. In the second part of the study, riblets were applied on suction and pressure side of the cascade blades; two different manufacturing techniques, a rolling and a coating techniques, were applied. The rolling technique provides riblets with a width of 70 μm and the coated riblets (CRs) have a width of 50 μm. The wake measurements were performed using a three-hole probe at midspan of the cascade in order to determine the resulting losses of the reference blade and the blades with applied riblets. The detailed analysis of the measurements shows that the riblets have only a slight influence on the viscous losses in the case of the compressor application in this study. Finally, these results are discussed and assessed against the background of feasibility and effort of riblet applications within the industrial design and manufacturing process.</jats:p

Verschleißreduktion von Tiefziehwerkzeugen durch Geometrie- und Aktivflächenoptimierung

Um Karosserien leichter und effektiver zu gestalten ist der Einsatz von Leichtbauwerkstoffen, wie Aluminiumlegierungen und hochfesten Stählen, notwendig. So kann die Blechdicke reduziert und Gewicht eingespart werden. Jedoch führen höherfeste Stähle und die Adhäsionsneigung von Aluminium zu einem signifikanten Anstieg der Anforderungen an den Werkzeugwerkstoff. Um hohe Werkzeugstandzeiten und somit eine hohe Ressourceneffizienz hinsichtlich des eingesetzten Werkstoffs und der Rüstzeiten im Presswerk zu gewährleisten ist eine lokale Optimierung der hochverschleißbehafteten Oberflächen zielführend. Daher wurde im Rahmen dieses Teilprojekts zunächst ein FEM/BEM-Tool für eine zeiteffiziente und genaue Berechnung der auftretenden Belastungen der komplexen Tiefziehwerkzeuggeometrie entwickelt. Parallel zur Geometrieoptimierung des Werkzeugs wurde eine Laseroberflächenbehandlung zum erweiterten Verschleißschutz erforscht. Durch Kombination der Technologien ist eine höchstverschleißfeste Oberfläche erzielbar die zu gesteigerten Werkzeugstandzeiten als auch zu verbesserten Reproduzierbarkeiten in der Fertigung führt