The purpose of the present study is to assess the possibility of the so-called choking flutter in a transonic cascade operating under choking conditions. In the experiment, measurements of the unsteady aerodynamic moment acting on an aerofoil which is oscillating in pitch about the midchord in a transonic channel flow are performed for channel height-to-chord ratios H/c = 0·5−3 and oscillation frequencies up to 120 Hz. For a large channel height such as H/c = 3, the unsteady aerodynamic behaviour is similar to that of an isolated aerofoil, and the system will be aeroelastically stable in the transonic region as well as in the subsonic one. For smaller channel heights such as H/c = 0·5, however, the flow chokes and the aerodynamic behaviour becomes significantly different from that at large channel heights. As soon as a shock appears, i.e. in the incipient transonic region, the aerodynamic derivatives change discontinuously, so that the subsonic and transonic regions can be clearly separated. In this case, the aerodynamic damping becomes negative in the transonic region.

In order to understand the transonic features, a one-dimensional unsteady analysis is undertaken for small channel heights H/c [les ] 0·5. The numerical results show good qualitative agreement with the experimental ones, predicting in the incipient transonic region a discontinuous variation of the aerodynamic moment which results in system instability.

It is concluded that choking flutter may occur in transonic channel flow with a moderately small channel height when the passage is choked.