Control of squealer-tip leakage flow with perforated-rib coolant injection in an axial turbine cascade

A novel perforated-rib configuration is proposed for controlling the tip leakage flow at the rotor tip of an axial turbine.Three perforated-rib layouts are considered,wherein a perforated rib is installed at(A)the Suction-Side squealer(SS-rib),(B)the Pressure-Side squealer(PS-rib),and(C)the additional squealer along the blade Camber Line(CL-rib).A numerical method is used to show how the novel rib layouts affect the aerodynamic performance of the tip leakage flow.Results show that the coolant jets issuing from the perforated-rib injection holes penetrate deeper into the tip clearance than those in the baseline squealer-tip case,and how the perforated-rib coolant injection affects the tip leakage flow depends strongly on the rib layout.The PS-rib and CL-rib layouts appear promising for controlling the tip leakage flow,playing a significant role in reducing the total pressure loss and improving the turbine blade’s isentropic efficiency.In particular,under an injection mass flow ratio of 1%and a tip clearance of 1%blade span,the PS-rib layout reduces the leakage mass flow rate by 27%and increases the isentropic efficiency by 1.25%compared with those in the baseline squealer-tip case.Meanwhile,the advantages of the PS-rib layout in tip leakage control are confirmed under small and large tip clearances.

Numerical Investigations on the Steady and Unsteady Leakage Flow and Heat Transfer Characteristics of Rotor Blade Squealer Tip

The steady and unsteady leakage flow and heat transfer characteristics of the rotor blade squealer tip were conducted by solving Reynolds-Averaged Navier-Stokes （RANS） equations with k-co turbulence model. The first stage of GE-E3 engine with squealer tip in the rotor was adopted to perform this work. The tip clearance was set to be 1% of the rotor blade height and the groove depth was specified as 2% of the span. The results showed that there were two vortexes in the tip gap which determined the local heat transfer characteristics. In the steady flow field, the high heat transfer coefficient existed at several positions. In the unsteady case, the flow field in the squealer tip was mainly influenced by the upstream wake and the interaction of the blades potential fields. These unsteady effects induced the periodic variation of the leakage flow and the vortexes, which resulted in the fluctuation of the heat transfer coefficient. The largest fluctuation of the heat transfer coefficient on the surface of the groove bottom exceeded 16% of the averaged value on the surface of the squealer tip.

Effects of Suction Side Squealer Tip on the Performance of a Low-Speed Axial Compressor

This paper presents the investigation of the effects of suction side squealer tip on the performance of an axial compressor. The experiment is carded out in a single-stage large-scale low-speed compressor. The investigated tip geometries include fiat tip as the baseline and suction side squealer tip. The tip clearance of the baseline is 0.5% of the blade span. The static pressure rise characteristic curves of both the rotor and the stage are measured. The flow field at the exit of the rotor is measured by a 5-hole probe under design and off-design conditions. The static pressure on the endwall of the rotor passage is also obtained. The results show that the pressure rise characteristic curves obtained by measuring the pressure on the end wall are almost unchanged by using the suction side squealer tip. The measuring results of the 5-hole probe show the static pressure and the total pressure in tip region is slightly greater than that of the flat tip at the design condition at the exit of the rotor. It also leads to greater averaged static pressure rise and total pressure. At the near stall condition, the averaged static pressure and total pressure is lower than the baseline which is related to the redistribution of the blade load caused by the suction side squealer tip.

Effects of Squealer Geometry of Turbine Blade Tip on the Tip-Leakage Flow and Loss

The effective control of the tip-leakage flow and loss is of great significance to improve the aerodynamic performance of the turbine.In this paper,the evolution mechanism of tip-leakage flow in a transonic high pressure turbine with a squealer tip is investigated with numerical simulation methods.The impacts of squealer geometric,such as the inclined pressure side rim and squealer rim width,on the vortex structure in the gap and tip-leakage loss are discussed.The results show that the scraping vortex inside the cavity plays the role of aero-labyrinth seal,and forms interlocking sealing labyrinth structure with the rims on both sides,which has an effective sealing effect on the tip-leakage flow.The inclined pressure side squealer rim inhibits the development of the pressure side squealer corner vortex,which is beneficial to expand the influence range of the scraping vortex and enhance the sealing effect on the tip-leakage flow.The increase of the suction side squealer rim width reduces the effective flow area at the gap exit,which is conducive to reduction of the tip-leakage flow rate and tip-leakage loss.However,the increase of the pressure side squealer rim width strengthens the pressure side squealer corner vortex and limits the development space of the scraping vortex,causing the adverse effects on the control of tip-leakage flow.

Effect of Squealer Tip with Deep Scale Depth on the Aero-thermodynamic Characteristics of Tip Leakage Flow

In this paper,the aero-thermal performance of squealer tips with deep-scale depth is numerically investigated in an axial flow turbine,which is compared with the squealer tip with traditional cavity depth.Numerical methods were validated with experimental data.The effect of cavity depth and tip clearance was considered.The numerical results show that for the squealer tip with conventional cavity depth,the size of the reflux vortex enlarges as the cavity depth increases.The velocity and uniformity of high entropy production rate(EPR)inside the cavity reduce obviously with the cavity developing into deep-scale.However,the increase of depth 10%of the blade span(H)leads to enlargement of cavity volume,which increases the total entropy production rate.And the overall dimensionless entropy production rate(DEPR)of gap and cavity obtains a maximum increase of 43.54%in contrast to the case with 1%H depth cavity.As a result,the relative leakage mass flow rate reduces by 20.6%as the cavity depth increases from 1%to 10%.Given the heat transfer,as the cavity significantly increases to 10%H,the enhanced cavity volume results in a more enormous cavity vortex with low velocity covering the floor,which weakens the convective heat transfer intensity and reduces the area of high heat transfer.The normalized average heat transfer coefficient at the cavity bottom reduces by 40.26%compared to the cavity depth of 1%H.In addition,the deep-scale cavity is more effective in inhibiting leakage flow at smaller tip clearance.The reduction amplitude of normalized average heat transfer coefficient at the squealer floor decreases as tip clearance increases,which reduces at most by about 72.6%for the tip clearance of 1%H.

Film cooling effects on the tip flow characteristics of a gas turbine blade

An experimental investigation of the tip flow characteristics between a gas turbine blade tip and the shroud was conducted by a pressure-test system and a particle image velocimetry(PIV)system.A three-times scaled profile of the GE-E3 blade with five film cooling holes was used as specimen.The effects on flow characteristics by the rim width and the groove depth of the squealer tip were revealed.The rim widths were(a)0.9%,(b)2.1%,and(c)3.0%of the axial chord,and the groove depths were(a)2.8%,(b)4.8%,and(c)10%of the blade span.Several pressure taps on the top plate above the blades were connected to pressure gauges.By a CCD camera the PIV system recorded the velocity field around the leading edge zone including the five cooling holes.The flow distributions both in the tip clearance and in the passage were revealed,and the influence of the inlet velocity was determined.In this work,the tip flow characteristics with and without film cooling were investigated.The effects of different global blowing ratios of M=0.5,1.0,1.3 and 2.5 were established.It was found that decreasing the rim width resulted in a lower mass flow rate of the leakage flow,and the pressure distributions from the leading edge to the trailing edge showed a linearly increasing trend.It was also found that if the inlet velocity was less than 1.5 m/s,the flow field in the passage far away from the suction side appeared as a stagnation zone.

Flowfield and Heat Transfer past an Unshrouded Gas Turbine Blade Tip with Different Shapes

This paper describes the numerical investigations of flow and heat transfer in an unshrouded turbine rotor blade of a heavy duty gas turbine with four tip configurations. By comparing the calculated contours of heat transfer coefficients on the flat tip of the HP turbine rotor blade in the GE-E3 aircraft engine with the corresponding ex- perimental data, the K：-o~ turbulence model was chosen for the present numerical simulations. The inlet and outlet boundary conditions for the turbine rotor blade are specified as the real gas turbine, which were obtained from the 3D full stage simulations. The rotor blade and the hub endwall are rotary and the casing is stationary. The influ- ences of tip configurations on the tip leakage flow and blade tip heat transfer were discussed. It＇s showed that the different tip configurations changed the leakage flow patterns and the pressure distributions on the suction surface near the blade tip. Compared with the flat tip, the total pressure loss caused by the leakage flow was decreased for the full squealer tip and pressure side squealer tip, while increased for the suction side squealer tip. The suction side squealer tip results in the lowest averaged heat transfer coefficient on the blade tip compared to the other tip configurations.

A novelapproachforsuppressingleakage flow throughturbinebladetipgaps

Tip clearance leakage flow of the turbine bade is an important factor limiting the augment of the high pressure turbine efficiency,which should be suppressed utilizing certain methods.However,the passive control method with the traditional structure is more and more difficult to satisfy the suppressing ability of the advanced turbine demand.In the present paper,a synergetic suppressing method by combining the approach of blade shape modification and spontaneous injection is adopted,to construct a novel tip structure.The aerodynamic characteristics of the tip leakage flow(TLF)with different blade tip configurations,such as the squealer,squealer-winglet(SW)and squealer-winglet-spontaneous injection holes(SWS)composite configurations,are numerically investigated.The impacts of several key geometric parameters,such as the winglet width and the space ng of spontaneous injection holes,are also discussed.Due to the adjustment of the winglet,the SW tip configuration can get better suppressing effect on TLF than the squealer tip.The SWS synergetic suppression tip decrease the leakage flow rate and the leakage mixing loss on the basis of the SW tip due to the blocking effect of the spontaneous injection flow.The key geometric parameters study shows that the suppressing effect of the TLF can be improved by reasonably increasing the winglet width and reducing the spacing between spontaneous injection holes.