Investigation on the Unsteady Aerodynamic Force on a 3:2 Rectangular Section under Accelerating Airflow

Unsteady characteristics of aerodynamic force and wind-induced pressure on a 3:2 rectangular section under accelerating airflow are investigated through wind tunnel experiments. Three aerodynamic coefficients, drag coefficient C_d(t), RMS of lift coefficient C_l^rms(t), Strouhal number of the rectangular section in the accelerating airflow with or without initial velocity are compared with those of the steady flow. Results show that in the cases of airflow accelerated from the static state, significant unsteady feature appears in all three aerodynamic coefficients, 𝐶𝐶𝑑𝑑(𝑡𝑡) and

C_l^rms(t) decreases and St number increases in the early accelerating stage. For accelerating airflow with an initial velocity, the three aerodynamic characteristics fit well with steady flow values, indicating negligible impact on any of these variables.