Abstract:

This paper develops a skin friction measurement technique based on skin friction balance for rarefied flow applications， and applies the technique to improve surface smoothness and reduce drag. A comparative measurement experiment is conducted in a hypersonic low-density wind tunnel， involving flat plate models and skin friction balances with smooth and conventional wall surfaces. The flat plate models are arranged symmetrically with smooth and conventional wall surfaces， each paired with skin friction balances having induction surfaces corresponding to the wall surface type. The balance structure is designed based on the cantilever beam principle， considering overload protection and thermal insulation. Micro-friction loading is achieved through load increment method to calibrate the balance closest to the experimental conditions. Through quantitative evaluation and active control， the error in wind tunnel tests introduced by surface pressure can be controlled within 1% and the error introduced by the offset installation of the balance floating head can be controlled within 2%. Seven repetitive tests at the Mach number of 22 show that the measurement standard deviation of skin friction balance is less than 2.9%； the smooth wall surface is more effective in reducing drag compared to the conventional wall surface， with an average drag reduction rate of 25.1%.

Key words: rarefied regime, skin friction balance, smooth wall surface, drag reduction, wind tunnel test, error controll