Effect Of Labyrinth Seal Structure On Flow Field Of Shrouded Turbine Blade Tip And Its Mechanism

Turbine,as one of the three most important components of gas turbine,its' performance has a significant influence on the performance of the whole gas turbine.In the flow field of turbine,the loss resulted by tip clearance leakage flow and other related phenomenon inside the land-based gas turbine and aircraft aero-engine covers a large part,as much as one third,of the whole loss.Problems lead by tip clearance gain more and more attractions now.One of the efficient method to mitigate the tip leakage flow is to introduce labyrinth seal onto the blade tip region.The labyrinth seal is widely used in low-pressure turbine because its well aerodynamic performance and structure characteristics,especially for shrouded turbine.Due to the complexity of the shrouded turbine structure,the flow condition and thermal processing is quite complex.After flow out the cavity,the tip leakage flow would mix with the main flow and further reduce the turbine performance.The main subject of this paper starts from studying the structure of labyrinth seal in a transonic shrouded turbine stage.An efficient labyrinth seal could effectively control the leakage flow and reduce the loss brought by tip leakage flow,then the aerodynamic performance of turbine would improve.The present paper intends to improve the flow field by revising the labyrinth seal structures.Three cases(doubleside labyrinth seal,casing-side labyrinth seal and blade tip-side labyrinth seal)are studied.After modeling and simulating the three cases as well as the baseline case,the effect of different labyrinth seal structure on the tip leakage flow is analyzed and their interaction mechanism is explored.First,the three different labyrinth seal structures are modelled based on the original shrouded turbine rotor blade,and steady RANS calculation are conducted to these four cases.The results show that all of the three labyrinth seal structures could mitigate the mass flow rate of the tip leakage flow.Specially,casing-side labyrinth seal and double-side labyrinth seal could effectively increase the efficiency of turbine stage,the maximum efficiency improvement could reach to 0.72% for double-side labyrinth seal case,and the mass flow rate of tip leakage flow reduce from 3.02% to 1.07% of the rotor inlet mass flow rate.For the blade tip-side labyrinth seal case.Later,the effect of tip clearance size and inlet total pressure on the control performance of labyrinth seal are studied.At different tip clearance size,the doubleside labyrinth seal case could effectively increase the turbine stage efficiency and reduce the mass flow rate of tip leakage flow.As the tip clearance size increasing,the increment of tip leakage flow mass flow rate of all three labyrinth seal cases are lower than that of the baseline case.Especially for double-side labyrinth seal case,it achieve the lowest tip leakage flow mass flow rate increment.At different inlet total to exit static pressure ratio,all three labyrinth seal cases reduce the tip leakage flow mass flow rate effectively.Especially,the double-side labyrinth seal case gain the best control performance,and has the largest efficiency improvement.As inlet total to exit static pressure ratio increasing,several shocks emerge,and has an adverse influence on the flow field.Finally,Time Transformation scheme is applied to study the unsteady performance inside the cavity.The results show that after introducing labyrinth seal structure,the variation of efficiency reduce from 4.6% to 4%,and the maximum efficiency could even reach to 93.4%.All three labyrinth seal cases could effectively control the tip leakage flow.The double-side labyrinth seal has the best performance among the whole period.The casing-side labyrinth seal and blade tip-side labyrinth seal,however,only control the tip leakage flow mass flow rate at part of the period.