Numerical Simulation Of The Influence Of Honeycomb Casing On The Performance Of Turbine Stage

With the development of turbomachinery, high-temperature, high-pressure, high-load, high-speed has become a trend. The tip-leakage losses become a major loss in turbomachinery. The selection of sealing structure is the key to reduce tip-leakage losses and improve efficiency. The method of numerical simulation is adopted. Comparing the turbine with honeycomb casing and the turbine with coating casing in steady characteristics and unsteady characteristics to provide theoretical reference for the selection of sealing structure in engineering.In the steady state calculation, the sealing structures improve the flow state in the upper part of stator passage by reducing the area of low pressure on suction surface and the shock loss on the trailing edge. By reducing the flow area in tip clearance and increasing the role of casing retardation, sealing structures can reduce the leakage and the strength of leakage vortex thus improving the efficiency and the ability to work of turbine.Wake, shockwave of upstream blade row flow through rotor passage periodicity for the relative movement between stator and rotor. They go through these processes including cut, moving, recession, and experience interactions with the fluid in rotor passage thus reducing the efficiency of the turbine stage. In stator passage, the unsteady phenomenon concentrates on the trailing edge, however, the interference affects the whole rotor passage periodicity. The interference changes the pressure field of tip clearance, altering the strength of leakage vortex periodicity. When the pressure differential is larger, so do the leakage and leakage loss. Suppressed by the up passage vortex, the interference in the upper part is weaker than the interference in the middle part.The fluid through honeycomb casing will be spilt into small vortexes which increases the dissipation capacity, what’s more, the fluid out of honeycomb casing will form a barrier which increases the resistance and get a good sealing effect. Compared with coating casing, honeycomb casing can be better to reduce the leakage and the strength of leakage vortex and shockwave and delay the development of leakage vortex, so that the turbine with honeycomb casing has more ability to work. However, the location of leakage vortex is lower, which increase the mixing degree between leakage vortex and passage vortex, so that the turbine with honeycomb casing has a less efficiency. What’s more, the amplitude of one time frequency which is caused by interference and make the rotor blade vibrate in honeycomb casing is smaller than that in coating casing.