Performance of a single-stage turbine as affected by variable statorarea

Moffitt, T. P.; Schum, Harold J; Whitney, W. J.

doi:10.2514/6.1969-525

Cited by 15 publications

(13 citation statements)

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“…Qiu et al 5 presented a new ''bottomup'' method that could predict the steady performance of variable geometry turbines. Examined against the turbine experimental data by Moffitt et al, 2 the computational results show good agreements with the experimental results. It can also be employed to predict the performance of multistage turbines with variable geometry used in each stage.…”

Section: Introductionsupporting

confidence: 57%

“…The concept of using variable geometry turbines to alter the gas turbine characteristics has been in existence for a lot of years, and there are some publications about the effects of variable geometry on the turbine efficiency. Moffitt et al 2 summarized the experimental results of the one-stage turbine investigated at different stator vane setting angles.…”

Section: Introductionmentioning

confidence: 99%

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Experimental and numerical investigations of tip clearance flow and loss in a variable geometry turbine cascade

Gao

Wang

et al. 2017

Proceedings of the Institution of Mechanical Engineers, Part A:

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Variable geometry turbines are widely employed to improve the off-design performance of gas turbine engines; however, there is a performance penalty associated with the vane-end partial gap required for the movement of variable vanes. This paper is a continuation of the previous work and aims to understand the leakage flow and loss mechanisms under the influence of the pivoting axis. Experimental investigations with a variable geometry turbine linear cascade have been conducted for tip gap heights of 1.1% and 2.2% blade spans as well as setting angles of À6 , 0 , and 6 , so as to reveal the three-dimensional clearance flow characteristics associated with partial gaps. Besides, numerical predictions are also carried out to better understand the experimental results. Pressure measurements were performed on the tip endwall as well as on the vane surface, and three-dimensional clearance flow fields downstream of the variable cascade were measured with a five-hole probe. The results show that as the vane setting angle is changed from design to closed, the vane loading increases and tends to be more aft-loaded, thus increasing the tip leakage loss, and vice versa. There are strong interactions between the flow around the pivoting axis and the leakage flow in the vane tip rear part, which leads to a low-pressure region on the tip endwall. The leakage vortex core is made up of the leakage flow in the vane tip rear part at both two tip gap heights, and the leakage vortex core formation process is different from the one in the rotor blade. The present results can provide useful references for the vane-end clearance design of variable geometry turbines.

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Section: Introductionsupporting

confidence: 57%

Section: Introductionmentioning

confidence: 99%

Experimental and numerical investigations of tip clearance flow and loss in a variable geometry turbine cascade

Gao

Wang

et al. 2017

Proceedings of the Institution of Mechanical Engineers, Part A:

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“…Qiu et al 5 proposed a new small deviation model that can predict the steady-state aerodynamic performance of variable geometry turbines. Checked against turbine test data (Moffitt et al 2 ), the predicted results present reasonable agreement with the test results. Also, it is used to predict the performance characteristics of multistage turbines with variable geometry used in any turbine stage.…”

Section: Introductionsupporting

confidence: 57%

“…The variable geometry turbine concept has been put forward to alter the gas turbine engine characteristics for a lot of years, and there are some open literatures about variable geometry effects on the aerodynamic efficiency of turbines. Moffitt et al 2 summarized the experimental data of the singlestage turbine studied at various vane turning angles. Their research work showed that the turbine isentropic efficiency reduces at each given pressure ratio when the vane turning is varied from design to either closed or open.…”

Section: Introductionmentioning

confidence: 99%

Improved clearance designs to minimize aerodynamic losses in a variable geometry turbine vane cascade

Gao

Wei

Liu

et al. 2017

Proceedings of the Institution of Mechanical Engineers, Part C:

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Variable geometry turbine exists in small mobile gas turbines or some marine gas turbines to enhance the part-load performance. However, there are efficiency penalties associated with the vane partial gap, which is needed for the movement of variable vanes. This paper investigates the vane-end clearance leakage flow for a flat tip, a cavity tip, a winglet tip, a tip with passive injection, and a cavity-winglet tip to assess the possibility of minimizing vane-end clearance losses in a variable geometry turbine cascade. First, calculations were done at the test rig conditions for comparison with measured data, and they were used for validation of computational fluid dynamics model. Then, numerical calculations were done for turbine typical conditions. Specific flow structures of the various clearance designs of variable vanes are described, and then the effects of vane turning, including exit Mach numbers of 0.34, 0.44, and 0.54 as well as turning angles of –6°, 0°, and 6° on total pressure losses and outflow yaw angle for different vane tips are shown. In addition, the sensitivity of aerodynamic losses to vane tip gap height is evaluated. Results show that the strong interactions near the tip endwall region change the near-tip loading distribution significantly. With winglet and cavity-winglet tip designs, the loading distribution becomes very similar to the typical fixed vane, and the total loading is reduced, thus reducing the vane-end losses. Among the different vane tips presented, the cavity-winglet tip achieves the best aerodynamic performance, and the cavity tip has the lowest sensitivity to vane tip gap height. Overall, the cavity-winglet tip is found to be the best choice for variable vanes. The research results can provide useful reference for the vane design in a real high endwall-angle variable geometry turbine.

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“…The choked mass flow is directly proportional to the effective turbine area but due to a reduction in Guide Vanes --Open Closed Fig. 9 The Effects of Turbine Area on Stage Losses [Moffit et al, 1969] nozzle flow coefficient (defined as the ratio of effective area to actual area) as the stators are opened, the change in the effective area is lesser than the change in the actual area, and if choking occurs somewhere else within the turbine other than at the stator, the nozzle coefficient is even lower. As a result, it is possible that for certain duties, the desired mass flow cannot be passed due to the excessive stator swing that may be required under certain operating conditions.…”

Section: Turbine Non-dimensional Mass Flowmentioning

confidence: 99%

Some Aspects of Variable Geometry Gas Turbine Operation

Roy-Aikins

1992

Volume 2: Aircraft Engine; Marine; Microturbines and Small Turbomachinery

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Many gas turbine thermodynamic cycles have been proposed which were designed to meet the propulsion requirements of future advanced aircraft. A thoughtful consideration of such designs is warranted as engines operating on such cycles will give a significant improvement in off-design performance. Such performance improvements can be brought about chiefly by the extensive use of variable geometry components. With the advent of the variable area turbine, a greater flexibility will be obtained in engine control and, hence, in aircraft operation. This paper examines the performance of a variable geometry engine that is suitable for V/STOL aircraft operation, and it discusses how certain aerodynamic and mechanical phenomena associated with variable area turbines may influence the design and limit the operation of future advanced gas turbines.

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Performance of a single-stage turbine as affected by variable statorarea

Cited by 15 publications

References 0 publications

Experimental and numerical investigations of tip clearance flow and loss in a variable geometry turbine cascade

Experimental and numerical investigations of tip clearance flow and loss in a variable geometry turbine cascade

Improved clearance designs to minimize aerodynamic losses in a variable geometry turbine vane cascade

Some Aspects of Variable Geometry Gas Turbine Operation

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