An article by The Aeronautical Journal examines the increasingly crucial role played by Computational Fluid Dynamics (CFD) in the analysis, design, certification, and support of aerospace products. The status of CFD for the aerospace engineer is described, and opportunities for CFD are identified where they could have a more substantial impact. The challenges facing CFD are also discussed, primarily in terms of numerical solution, computing power, and physical modelling. We summarize the report in this article.Simulation Challenges & Limitations Of The Aerospace Engineer
Primarily addressing those areas where practical improvements could be made, the article also appraises how CFD has enabled gradual developments to be made in both commercial and military spheres.
As the engineering community continues to work to provide the most efficient, effective and productive software solutions, the article’s “industry view” is extremely useful and informative, gaining an understanding of shifts not only in its practical use, but also in attitudes.
CFD Simulation For The Aerospace Engineer
CFD has played a key role in the development of both commercial and military aircraft, with the design of the high-speed wing and its integration with the engine, particularly well profiled over past years. Boeing is a solid example of a company that has truly embraced CFD, first harnessing its benefits in the development of the Boeing 737 during the 1980s. The extent to which it has become an integral part of commercial aircraft design, is evident in a ‘walk-around’ chart (Fig.1) released by Boeing. Industry competitor Airbus, also takes a proactive approach to its aircraft design processes, producing similar charts for its aircraft.
Fig. 1 Impact of CFD at Boeing. Red: Future Opportunities. Green: Strong CFD penetration Blue: Some CFD penetration.
The Future Of CFD Simulation For The Aerospace Engineer
The report authors believe aerospace engineers must find a balance between enthusiasm and rigor. Besides becoming faster and more affordable by exploiting higher computing power, CFD needs to become more reliable, more reproducible across users, and better understood and integrated with other disciplines and engineering processes. Uncertainty quantification is universally considered as a major goal, but will be slow to take hold.
The prospects are good for steady problems with Reynolds-Averaged Navier- Stokes (RANS) turbulence modelling to be solved accurately and without user intervention within a decade – even for very complex geometries, provided technologies, such as solution adaptation are matured for large three-dimensional problems. On the other hand, current projections for supercomputers show a future rate of growth only half of the rate enjoyed from the 1990s to 2013; true exaflop performance is not close. This will delay pure Large- Eddy Simulation (LES) for aerospace applications with their high Reynolds numbers, but hybrid RANS-LES approaches have great potential. The author's expectations for a breakthrough in turbulence, whether within traditional modelling or LES, are low and as a result off- design flow physics including separation will continue to pose a substantial challenge, as will laminar-turbulent transition. We also advocate for much improved user interfaces, providing instant access to rich numerical and physical information as well as warnings over solution quality, and thus naturally training the user. Don't forget, if you're new to CFD, check out our Essential Guide.
Flight Test, Wind Tunnel or CFD?
Increasingly, CFD results are compared directly with flight test, rather than wind tunnel, and the status of the two sources of information in the aerospace engineering process and company culture is slowly shifting, with enlightened organisations drawing on both to good effect. It is important to transition from wind tunnel to CFD for the right reasons, such as wall effects or Reynolds number and aeroelastics, whereas doing so only for speed and cost advantages has its dangers. The authors of the report believe there is a tendency towards overconfidence in CFD in some circles, even to the extent of ignoring well-known sources of error, which creates a risk of backlash, were CFD to be blamed for costly mistakes.
There’s no doubt as to the possible advantages of transitioning from wind tunnel to CFD, but doing so for the right reasons is essential. While striving to increase speed-up and reduce costs is an important aspect, it cannot be to the detriment of final outcomes. Inaccuracies not only bring financial consequences, but also threaten to diminish confidence in results.
Skill-Level Of The Aerospace Engineer
The paper brings into question not only the skill set of those aerospace engineers using HPC processes and software, but also attitudes and carelessness. With relentless time and cost pressures facing engineers, the skill level of those using CFD has also been addressed as a potentially concerning factor, no doubt contributing careless inattentions or failings.
With the various CFD phases such as geometry preparation, gridding, solution set-up and post processing, requiring a considerable level of proficiency, addressing the lack of formal training undertaken by software users is an industry priority, and could easily address the concerns of competence. One of the key conclusions, is that more training should be largely encouraged, enforcing a user’s ‘situational awareness’.
Overcoming Time Constraints Of The Aerospace Engineer
The often lengthy turnaround time associated with CFD has limited its use in database design and creation, as well as presenting challenges for those aerospace engineers performing multi-disciplinary applications. In fact, the time required to prepare geometries for grid generation and aerodynamic analyses, has encouraged both tasks to remain mostly manual. While the world of CFD has enjoyed significant growth in computing power over recent decades, recent slow-downs have caused widespread concern, with computer scientists grappling to come up with solutions that enable progress to continue at a desirable rate.
A slow-down in computer power would delay pure Large-Eddy Simulation (LES) for aerospace applications, but hybrid RANS-LES approaches carry much more potential. Newer solvers such as EXN/Aero are enabling powerful supercomputing processes to be more accessible to aerospace engineers, and the paper urges companies to continue in this vein, identifying ways to address the slow-down of Moore’s Law.
CFD: An Essential Tool For The Aerospace Engineer
The paper attributes CFD as the increasing power, enabling barriers to be broken down between disciplines, and enabling higher accuracy standards when used correctly and appropriately. While progress is expected to remain steady, CFD is expected to contribute to the widely held concern that aircraft programs take too long and cost too much.
It is hoped that CFD will improve the economics of conventional aircraft, and also allow exploration into new concepts, such as supersonic transport with acceptable fuel-burn and sonic-boom penalties. Opportunities for aerospace engineering in the exascale era are being cautiously explored, and a paper produced by the University of Wyoming’s Department of Mechanical Engineering, sets out the vision held by NASA and Boeing, part of the NASA Vision CFD2030 team.
Fig 2. Simulation tools will continue to play a key role in the aerospace engineer's toolkit
Envenio's EXN/Aero For The Aerospace Engineer
With regards to the slow-down of Moore’s Law, Envenio continues to provide supercomputing solutions at an accessible and affordable level through its on-demand, pay-as-you-use cloud platform EXN/Aero. As well as focusing on the development of its interface, Envenio’s commitment to education and training is also strong, and the introduction of the Onboarding Program, whereby aerospace engineers are trained on the platform while setting up their first simulation, is just one example. Envenio also offers outsourcing options including the Discovery Project.