Improving the Interaction Between Leakage Flows and Main Flow in a Low Pressure Turbine

Abstract

A large part of the losses caused by leakage flows through cavities in turbines are mixing losses. They arise when the leakage flow — after passing through the cavity — is re-entering into the mainflow. In the zone of re-entering, the velocity components of the mainflow differ from those of the leakage flow, since the former has passed the precedent airfoil, where it has been accelerated and turned, while the latter has not. This leads to shear stresses which cause increased turbulence and losses. This paper presents a numerical investigation of a device which reduces the mixing losses caused by the leakage flows through inner cavities of a low pressure turbine to 63% of their original value. The device is situated close to the rear openings of the cavities and a large part of the leakage flow is passing through it. The leakage flow is turned and accelerated by the device in a way that brings its velocity components closer to the velocity components of the mainflow. This reduces the mixing losses considerably compared to cavity flows without turning devices. An increase in efficiency of the low pressure turbine of about 0.1% can be noticed. This paper presents numerical results of steady 3D simulations of a three-stage low pressure turbine with a pressure ratio of approximately 3.5. Results with an ideal flow path (no cavities), with inner cavities without turning device and with inner cavities with turning device are compared. Radial distributions of characteristic quantities (turbulent kinetic energy, circumferential velocity etc.) show that these quantities evaluated with cavities with turning device are much closer to the ideal flow path quantities than without. By subtracting the solution with turning device from the one without, the regions where mixing losses are reduced are identified.

Experimental and numerical validation study of the labyrinth seal configurations

“…The GGI can affect the flow conditions but it makes it possible to use an independent, denser mesh in the honeycomb and in the main channel. The GG was previously used with success in (Wittig, 1985), (Mahle, 2010), (Gao et al, 2013). A mesh-independence study was performed by comparing the C D value (cf.…”

Dimensionless Numbers Relationships for Outer Air Seal of Low Pressure Turbine

“…For the previously mentioned reasons, the IAS regions were the first to attract the interest of many research groups attempting to optimize the device performance. There exist well-performing solutions of IAS, such as the brush seals investigated for instance by Dinc et al [1], or the turning devices by Mahle [2].…”

Comparative investigation of tip leakage flow and its effect on stage performance in shrouded and unshrouded turbines

“…36 In spite of the inherent limitations of this interface, acceptable agreement between measured and predicted data can still be realized. 33,43 In the work of Gier et al 24 and Mahle, 29 'Frozen Rotor' interfaces were used to connect the shroud cavity and the main passage. They also compared the numerical simulation with experimental data, and obtained a pretty reasonable computation quality.…”

“…The physics of secondary path flows (shroud leakage, cavity and cooling flows), and their interactions with the main flow have been intensively investigated. 1,[22][23][24][25][26][27][28][29] Furthermore, a range of investigations is also dedicated to geometric modifications of shroud cavities and their consequences of the interaction between shroud leakage flows and main flows. [30][31][32][33][34] These geometrical modifications directly aim at reducing mixing losses and subsequent row losses by influencing the velocity components of the shroud leakage flow.…”