Abstract : Experiments have been carried out in plane and axisymmetric sudden-expansion flows to quantify velocity characteristics in isothermal and reacting flows and temperature and emission characteristics in the reacting flows, to establish flammability and stability limits, to determine the acoustic characteristics and their importance to large-amplitude oscillations and to examine the nature of extinction. Flow visualization and detailed measurements quantified the asymmetry of the plane flows and the extent to which it was removed by combustion. Longitudinal waves dominated the flows in both ducts for an extensive range of equivalence ratios and active control was successful in reducing amplitudes except where the frequencies were broad band as at higher equivalence ratios and close to flammability limits. Close to these limits, oscillations existed with frequencies much lower than those associated with acoustic or bulk-mode frequencies and with modulation rather than the single-frequency oscillations associated with equivalence ratios between around 0.75 and 1.2. Models of the combustor of a land-based gas turbine were examined, one with an annular main flow and a central pilot flow and the other with swirl stabilization. in the first arrangement, the movement of flame stabilization from the annular ring to the back step was important and, in the latter, the position of stabilization also moved but this time axially with increasing load so that the fixed position of the actuator for active control proved to be satisfactory for some load conditions and less so for others.