Active Flow Control on Vertical Tail Models

Abstract

Active flow control (AFC) subscale experiments were conducted at the Lucas Wind Tunnel of the California Institute of Technology. Tests were performed on a generic vertical tail model at low speeds. Fluidic oscillators were used at the trailing edge of the main element (vertical stabilizer) to redirect the flow over the rudder and delay or prevent flow separation. Side force increases in excess of 50% were achieved with a 2% momentum coefficient (C _μ ) input. The results indicated that a collective C _μ of about 1% could increase the side force by 30-50%. This result is achieved by reducing the spanwise flow on the swept back wings that contributes to early flow separation near their tips. These experiments provided the technical backdrop to test the full-scale Boeing 757 vertical tail model equipped with a fluidic oscillator system at the National Full-scale Aerodynamics Complex 40-by 80-foot Wind Tunnel, NASA Ames Research Center. The C _μ is shown to be an important parameter for scaling a fluidic oscillator AFC system from subscale to full-scale wind tunnel tests. The results of these tests provided the required rationale to use a fluidic oscillator AFC configuration for a follow-on flight test on the Boeing 757 ecoDemonstrator.

Fig. 1

Four model configurations tested at the Caltech Lucas Wind Tunnel.

Fig. 2

Dependence of side force on β for rudder deflections varying from 0° < δ_R < 40°, flow control off for AA model.

Fig. 3

Pressure coefficient, C_P, contours on the rudder suction side for baseline cases.

Fig. 4

Change in side force at U_∞ = 40 m∕s with actuator spacing of 1.5 in.

Fig. 5

Chordwise pressure distributions at U_∞ = 40 m/s with actuator spacing of 1.5 in. (38.1 mm) for sideslip angle,β = 0°, and rudder deflection, δ_R = 30°.

Fig. 6

Change in side force as a function of power and actuator spacing for the AA model.

Fig. 7

Comparison of pressure contours on the rudder for baseline (left), vortex generators (middle), and fluidic oscillators (right) for two rudder deflections.

Fig. 8

Difference image for δ_R = 20° rudder deflection, β = 0°, A_act = 1.0, Sp = 15%. The flow is from left to right.

Fig. 9

Effect of steady jets and jet orientation on model AA (Sp = 12%, C_μ = 0.3%, and δ_R = 30°).

Fig. 10

Dependence of side force and drag polars on nominal rudder angle for all four vertical tail configurations.

Fig. 11

Effect of AFC (C_μ = 1.5%) on C_Yn and C_D produced by the four vertical tail configurations.

Fig. 12

Variation of C_Yn and ΔC_Yn with C_μ at δ_R = 20°, 30°, and 35° rudder deflections, A_act = 1 and Sp = 3%.

Fig. 13

Percentage improvement in C_Yn by increasing C_μ at δ_R = 20°, 30°, and 35° rudder deflections,β = 7.5°, A_act = 1 and Sp = 3%.

Fig. 14

Drag characteristics for the four planforms at δ_R = 20°, 30°, and 35° rudder deflections,β = 0°, A_act = 1,and Sp = 3%.

Fig. 15

Effects of spacing on the side force generated by models AA and BB at δ_R = 30°.

Fig. 16

Flow visualization on model AA rudder for β = 0°, δ_R = 30°, Sp = 3% at increasing values of C_μ.

Fig. 17

Tuft visualization of surface flow over a deflected rudder with sparse actuation.

Fig. 18

Rudder leading edge cutouts and temporary covers.

Fig. 19

Side force generated by the rudder for the full-scale and subscale model configurations at sideslip angle, β = 0°

Fig. 20

Dependence of side force on C_μ at δ_R = 30° and β = 0°.