{'fraction_non_alphanumeric': 0.025547445255474453, 'fraction_numerical': 0.006569343065693431, 'mean_word_length': 5.120535714285714, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Experimental study on flat plate skin friction control by porous media based on global fluorescent oil film measurement technology

Skin friction is a primary source of total aircraft drag, and it is important, therefore, in science and engineering to achieve drag reduction control in a boundary layer. In this paper, under the experimental conditions of Re q=5909 (x/c=0.55), and with a zero-pressure gradient, the drag reduction control of a plate boundary layer in porous media is studied. The global skin friction of the plate is measured using fluorescent oil film test technology. The results show that, in contrast with the downstream frictional resistance coefficient of a flat plate that possesses a smooth surface, the coefficient for porous media reduced significantly. And the lower the pores-per-inch (PPI) of the porous media, the greater the drag reduction effect. Among the three porous media with different PPI, porous media with 10 PPI has the best drag reduction effect. With increasing distance from the porous media, the drag reduction effect decreases gradually. Porous media significantly increases the slope of the logarithmic region of the velocity profile of the downstream turbulent boundary layer, the dimensionless wall-velocity u+ moves upward, and the velocity pulsation in the logarithmic region increases, so as to reduce skin friction.