Jet methods of gas injection into fluid boundary layer for drag reduction

Two jet methods for saturating the fluid boundary layer with microbubbles for drag reduction in contrust with gas injection through porous materials are considered. The first method is the gas injection through the slot under a special fluid wall jet. The second method is the saturation of boundary layer by microbubbles via the gas-water mixture injection through the slot. Experimental data, reflecting the skin friction drag reduction on the flat plate and total drag reduction of axisymmetric bodies, are presented. The comparison between a jet methods of gas injection and gas injection through porous materials is made.Nomenclature v free-stream velocity - v_j mean velocity of a water through slot - v_g mean velocity of a gas through slot - h width of slot for realizing water jet - h₁ width of slot for gas injection - incidence angle - Q volume airflow rate - C_Q airflow rate coefficient (v_g/v) - C_f skin friction coefficient - v_j/v - C_f0 C_f ifQ=0 andv_j=0 - _f C_f/C_f0 - d diameter of an axisymmetric body - L length of body - C_Q 4 · ·Q/d²v - C_D 4 ·D/1/2v²·d² - C_Q 4 ·Q/d²v - Q_j volume flow rate of water jet - C 8 ·Q_jv_j/d²v² - 1 fluid density of main flow - 2 fluid density of wall jet - B₁ main stream total pressure - B₂ wall jet total pressure - v₁ main stream velocity - Be (B₂ –B₁)/1/2₁v₁² = Bernoulli number - ₂v₂/₁v₁ - p_st static pressure - p_at atmospheric pressure - p_st/p_at - D hydrodynamic drag of body