WojtekSz
Does this tuning also include the frequencies induces but burning chambers? These seem to be a source of (possibly the most) significant energy vibrations within the engine case.
I think you will be surprised to learn that this is not a major concern in the combustor, and that is not to say vibrations are not created by the mixing and burning of the fuel. Vibration responses are looked at during the design phase using a sophisticated analysis program but, the major concern is that of LCF (eventual crack initiation) due to the thermal gradients throughout the engine cycle, i.e., cold to hot to cold. The reason vibration is not such a problem is the unique way it is handled. The "flame" is contained inside the combustor liner. The liner is "free floating" inside the combustor pressure vessel meaning it is not firmly attached to the pressure vessel in any way. The liner itself is cantilevered by bolting it to the stage 1 HPT nozzle ring. At the turbine nozzle attachment point, a 360° leaf seal is used to prevent hot gas leakage, but it also provides dampening. The actual liner is constructed from several individual pieces. The dome (front end where the fuel nozzles inject fuel) is one piece. It is bolted to the inner and outer liner walls with a series of self locking bolts. The bolts serve as dampers and prevent vibration from transferring to the fuel nozzles that are attached to the main fuel supply tube ring. So there is vibration but it is dealt with by unique design mechanisms to prevent it from being a problem.