Transition Prediction for Hybrid Laminar Flow Control Flight Test Considering Geometric Uncertainties

Abstract

Due to its significant capability for energy and environmental sustainability, the hybrid laminar flow control (HLFC) shows excellent technical appeal for civil aircraft. To use computational tools to speed up the HLFC design process, it is crucial to accurately predict the transition location and reveal the coupling mechanism of suction control and pressure gradient. We carry out HLFC wing glove flight experiments under different flight conditions. More than 40% chord laminar flow region is maintained for some flight conditions. We then perform numerical simulations based on the eN method. The good agreement between the deterministic simulation and experimental data indicates that the eN-based method using the critical N factor from natural laminar flow (NLF) can capture Tollmien–Schlichting (TS) instabilities for HLFC under similar conditions. For the HLFC simulation, the suction velocity is determined using an algebraic model as a boundary-layer condition, which is verified by the test data. We further consider geometric uncertainties to the laminar-to-turbulent transition prediction. We conclude that as long as TS instabilities are fully suppressed in the leading edge region, the variation of stochastic solutions about predicted transition locations is less than 8% chord for most flight conditions. Besides, experimental results locate in the given confidence intervals. For this wing glove test, both deterministic and uncertainty transition prediction results of the HLFC wing by using the critical N factor of TS waves calibrated throught NLF experiment agree with HLFC experiment well.