SBIR-STTR Award

Development and validation of a CFD method for determining heat flux rates during quenching of aircraft components is proposed. Current methods of managing the bulk residual stresses of machined aircraft forgings rely on experimental determinations of quenching heat fluxes that are costly, time-consuming, and subject to several types of errors. The proposed Phase I scope of work includes the development of several novel routines for the simulation of all modes of boiling heat transfer as well as the transition between these modes. Initial validations will be based on published data for each portion of the simulation method. The final validation will be based on new data collected on a representative part in a typical quench facility. Analysis of the quench data will include calculation of the experimentally determined heat fluxes and prediction of residual stresses based on CFD and test-based heat flux rates. Completion of this effort will establish the feasibility of developing a practical CFD-based tool for management of bulk residual stress.

Benefit:
A well developed CFD tool will provide more accurate and complete data, and will avoid the time and cost involved in manufacturing prototype parts for use in heat flux determinations. The higher quality data will be useful in developing improved manufacturing techniques, which will allow for the development of near-net shape forgings techniques. These improvements will directly impact the buy-to-fly ratio for these parts (the ratio of the forged weight to the final part weight) providing a direct reduction in manufacturing costs. In addition to extensive applications within the military and commercial aerospace communities, the proposed tool could be widely applied within the broader manufacturing industries. Data from 2006 suggests that the size of the commercial US heat treating market is greater than $20 billion. Improvement in the quench quality for the high value end of that market will represent a significant improvement in quality along with a reduction in scrap and rework rates.

Keywords:
Computational Fluid Dynamics, Heat Flux, Boiling Heat Transfer, Multiphase Flow, Aircraft Components, Quenching Processes, Cfd, Bulk Residual Stress

A proposal for a Phase II effort that continues the development of a computational fluid dynamics (CFD) based tool for the prediction of bulk residual stresses, started under the Phase I effort, is presented. The key objective in this proposal is to improve the numerical heat transfer methods explored in Phase I via experimentation, theoretical development, and validation. Small scale boiling experiments are suggested for improving the understanding of sub cooled oil boiling heat transfer. In particular, specific experiments are proposed for improving the understanding of nucleate site density, bubble departure size, transition boiling characteristics and film boiling vapor thickness. The experimental activities will provide an additional foundation that will be used to improve the understanding of the physics of boiling oil and help determine improved sub grid scale heat transfer relationships. Additional data for validating the methods will be collected in a pilot-scale facility on a full-size and representative part. An initial release of the software tool is expected at the end of the project, providing a solid foundation for a commercial CFD-based software product.

Benefit:
The primary benefits of the research outlined in this proposal is the development of an engineering software tool capable of predicting heat transfer on a forged part during the quenching process. Currently, there are no Computer Aided Engineering (CAE) software tools available for reliably approximating heat transfer during an oil quenching process. The proposed simulation tool is expected to improve the quality and reduce the costs of manufactured metal parts. In particular, it is expected that the software will provide the necessary tools for engineers to reduce post-heat treat machining and improve the uniformity of part material properties. The commercial product resulting from the proposed research will be the foundations of a software tool that can be applied to a number of parts manufactured for private and military applications. Parts for the military such as turbine disks, large bulk heads, helicopter gears and large gun barrels are some of the items that would benefit from design work that included the application of the software. The automotive industry utilizes large quantities of heat treated parts. Since the corporate culture in this industry is to design in part quality rather than inspecting for the desired part quality it could also benefit from the proposed design tool.

Keywords:
Computational Fluid Dynamics (Cfd), Heat Treating, Film Boiling, Nucleate Boiling, Residual Stress, Wall Heat Flux, Quenching