A flow around an NACA00 12 airfoil at special transonic flow conditions, characterised by damped oscillations of the main flow velocity, was investigated experimentally. On the basic of pressure measurements and flow visualisation, the time depending airfoil loading was reconstructed. Results, presented for a wide range of angle of attack ( a =Q-;-10°), show that during the excitation the normal aerodynamic force behaviour significantly differs from that of quasi- steady conditions. The pressure distributions on the airfoil surface depend on Mach number of the main flow as well on the phase of oscillation (deceleration or acceleration of the main flow velocity). The influence of the air humidity on the pressure distribution, normal aerodynamic force and centre of pressure is also considered.

The paper presents numerical simulations related to the problem of how to obtain correct results in transonic wind tunnel during tests at high airfoil angles of attack. At this flow conditions, significant pressure losses appear in the test section, what leads to significant errors in measured data. Regarding the possible ways of tunnel reconstruction, we examined three different possibilities of changing the test section configurations: an increase of the test section height, displacement of the airfoil below the tunnel centreline and, finally, introduction of divergent test section walls. It was shown that neither the use of higher test section, nor the change of the airfoil location, gives any significant improvement in reference to the existing tunnel configuration. Only after divergent test section walls were introduced, the distributions of pressure coefficient became well consistent with their expected values.

The effect of air humidity on oscillatory flow around the NACA 0012 airfoil was investigated experimentally at Mach number M=0.71 and airfoil angle of attack a=8.5''. The background tlow oscillations were produced by a rotating rectangular plate placed downstream of the airfoil. The generated oscillation frequencies were in the range from 0.5 up to 1.5 of the buffet frequency. The presented results shown that the normal aerodynamic force variations strongly depend on the excitation frequency and reach a maximum value at frequencies typical to the buffet. The increase of the air humidity leads to considerable diminishing of the aerodynamic force variation.

The characteristics of the free gas jet, during its interaction with an upstream moving shock, were investigated experimentally. The initial strength of the shock remained constant and equal to M, = 1.34 whereas the Mach number of the free gas jet M, varied in a wide range of sub- and transonic values from M, = O up to M, = 1.4. It is shown that in the presence of the moving shock the jet characteristic becomes strongly modified. Outside the jet originates a cluster of pressure waves which moves upstream in jet surrounding. Spatial and frequency characteristics, as well as the number of pressure waves in the cluster, depend on the shock amplitude and the exit velocity of the free gas jet.