Load balancing for chemically reacting flows. Issue 12 (4th December 2017)

• Record Type: Journal Article
• Authors: Löhner, Rainald; Togashi, Fumiya; Baum, Joseph David
• Is Part Of: International journal of numerical methods for heat & fluid flow. Volume 27:Issue 12(2017)
• Page Start: 2768
• Page End: 2774
• Publication Date: 2017-12-04
• Subjects: Load balancing -- Chemically reacting flows; Heat -- Transmission -- Mathematics -- Periodicals; Fluid dynamics -- Mathematics -- Periodicals; 536.2
• DOI: 10.1108/HFF-03-2017-0119
• Languages: English
• ISSNs: 0961-5539

Abstract

Abstract : Purpose: A common observation made when computing chemically reacting flows is how central processing unit (CPU)-intensive these are in comparison to cold flow cases. The update of tens or hundreds of species with hundreds or thousands of reactions can easily consume more than 95% of the total CPU time. In many cases, the region where reactions (combustion) are actually taking place comprises only a very small percentage of the volume. Typical examples are flame fronts propagating through a domain. In such cases, only a small fraction of points/cells needs a full chemistry update. This leads to extreme load imbalances on parallel machines. The purpose of the present work is to develop a methodology to balance the work in an optimal way. Design/methodology/approach: Points that require a full chemistry update are identified, gathered and distributed across the network, so that work is evenly distributed. Once the chemistry has been updated, the unknowns are gathered back. Findings: The procedure has been found to work extremely well, leading to optimal load balance with insignificant communication overheads. Research limitations/implications: In many production runs, the procedure leads to a reduction in CPU requirements of more than an order of magnitude. This allows much larger and longer runs, improving accuracy and statistics. Practical implications: The procedure has allowed the calculation of chemically reacting flow cases that were hitherto not possible. Originality/value: To the authors' knowledge, this type of load balancing has not been published before.