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Japan Aerospace Exploration Agency

Technology for testing the effects of the transonic Reynolds number

There are no high Reynolds number wind tunnels in Japan capable of replicating the Reynolds numbers (Re) that actual aircraft experience (the Reynolds numbers achieved when an aircraft or spacecraft actually flies in the air). However, Reynolds numbers have a massive impact on aerodynamic characteristics; in tests using conventional wind tunnels, the aerodynamic resistance correction amount for cruising operations sometimes exceeds 20% of the total resistance.

Although Reynolds number effects have drawn considerable attention from numerous researchers, Japan currently lacks the comprehensive knowledge and experience to have a solid grasp of the correction methods. The goal of this research, then, is to establish clear correction boundaries by making the most effective possible use of the available technologies. Quantifying the differences between the results from high Reynolds number wind tunnel tests and the results of computational fluid dynamics (CFD)-based predictions will also form a foundation for establishing aerodynamic characteristic prediction technologies within the context of the Reynolds numbers that actual aircraft encounter.

An example estimation of air resistance breakdown for a passenger aircraft configuration under assumed wind tunnel testing conditions in a 2m x 2m
transonic wind tunnel (here, "correction" refers to the Reynolds number correction amount)