Effects of Turbine Tip Clearance on Gas Turbine Performance

Abstract

There are many different sources of loss in gas turbines. The turbine tip clearance loss is the focus of this work. In gas turbine components such as compressor and turbine the presence of rotating blades necessitates a small annular tip clearance between the rotor blade tip and the outer casing. This clearance, although mechanically necessary, may represent a source of large loss in a turbine. The gap height can be a fraction of a millimeter but can have a disproportionately high influence on the stage efficiency. A large space between the blades and the outer casing results in detrimental leakages, while contact between them can damage the blades. Therefore, the evaluation of the sources of the performance degradation independently presents useful information that can aid in the maintenance action. As part of the overall blade loss the turbine tip clearance loss arises because at the blade tip the gas does not follow the intended path and therefore does not contribute to the turbine power output and interacts with the outer wall boundary layer. Increasing turbine tip clearance causes performance deterioration of the gas turbine and therefore increases fuel consumption. The increase in turbine tip clearance may as a result of rubs during engine transients and the interaction between the blades and the outer casing. This work deals with the study of the influence of the turbine tip clearance on a gas turbine engine, using a turbine tip clearance model incorporated to an engine deck. Actual data of an existing engine were used to check the validity of the procedure. This paper refers to a single shaft turbojet engine under development, operating under steady state condition. Different compressor maps were used to study the influence of the curve shapes on the engine performance. Two cases were considered for the performance simulation: constant corrected speed and constant maximum cycle temperature.

Massively Parallel Large Eddy Simulation of Rotating Turbomachinery for Variable Speed Gas Turbine Engine Operation

“…To investigate the effect of tip leakage flow through the clearance gap between rotor blade and the shroud, LES simulations were conducted for two values of tip clearance using the finest grid, Grid C. For the first case, a large tip clearance of 3.39 mm was used, which is equivalent to 16% of the rotor chord. The geometry was then revised for the second case to reduce the tip gap to 0.62 mm, resulting in a realistic 3% tip clearance Booth et al [12], Bringhenti and Barbosa [13] with respect to the rotor chord. Figure 15 compares the instantaneous velocity magnitude contours obtained for the two cases in the middle of the rotor section in a plane normal to the stream-wise direction.…”

“…Booth et al [12] found that the tip clearance of 1% results in 1-3% loss in turbine stage efficiency. By using a validated tip clearance model, Bringhenti and Barbosa [13] showed that the reduction in tip clearance allows for engine operation at lower temperatures because of improved efficiency. Other relevant studies have utilized idealized models for quantifying heat transfer and losses associated with tip clearance [14][15][16].…”

A Review on Tip Clearance Flow and Secondary Flow Losses in Linear Turbine Cascade

“…They found that increased tip clearance heights in the tip regions of two adjacent blades are blame for the larger clearance loss of the centre blade. Effects on turbine tip clearance on gas turbine performance studied by Cleverson Bringhenti and Joao Roberto Barbosa [9]. They observed that the tip clearance have very well affect on its performance and occurs losses.…”

A review of blade tip clearance–measuring technologies for gas turbine engines

“…6 And with further researches, a relationship was discovered by researchers that the decrease of the tip clearance reduces the fuel consumption of the engine at a given working point, as well as the working temperature. 7 Furthermore, if the tip clearance is too big, it will not only decrease the efficiency of the engine but also consume more fuel and even cause a surge. 8 On the contrary, the decrease in tip clearance can reduce the working medium leakage and the loss of the end wall, so as to improve the engine performance.…”