Optimizing LPT efficiency requires to minimizing airflow leakages between the static parts and the rotating parts. Firstly, bypass airflow are not working in the LPT which decreases LPT performance. Secondly, reintroductions of airflow into the flowpath make local pressure losses which decreases LPT performance. Integration issues, high operating temperature conditions and robustness requirements lead to design labyrinth seal at the top of the blades and under the distributors.
Fig.2 Schematic view of bypass airflows in a LPT
Labyrinth seals are the most common flow path seals applied to turbine engines. They consist of several knife edges, typically five, in close clearance (0.25 to 0.50mm) in a number of configurations (Fig.2). Labyrinth seals rely on controlled leakage across the seal. This is driven by the pressure differential between the seal ends. The design of the seal forces the flow to separate at the knife edge causing a loss of kinetic energy and pressure from the gas flow. This is repeated in the next cell and so on until the gas leakage reaches the seal exit. Current labyrinth seal applications can withstand temperatures as high as 700°C and pressure differences of up to 30 bars. However, vibration of the shaft can cause the blades to bite or rub into the shroud, increasing the flow between cells and reducing the sealing efficiency. Current advances in labyrinth seals focus on the use of abrasive knives and sacrificial ceramic shrouds to reduce leakage rates while allowing for rubbing to occur. Labyrinth seal design and optimization is based on pressure loss characteristics (reduced flow depending on pressure ratio) which take into account the seal geometry and the rotor speed.
SAFRAN Aircraft Engines has developed a numerical model to calculate the pressure loss characteristics of the labyrinth seals (Fig.3) and this model has been validated with partial test for a wide range of configurations.
SAFRAN Aircraft Engines has developed a numerical model to calculate the pressure loss characteristics of the labyrinth seals (Fig.3) and this model has been validated with partial test for a wide range of configurations.
Fig.3 Numerical model of the pressure loss characteristics developed by SAFRAN Aircraft Engines
The Engine ITD Leaders will perform the main activities related to the LP turbine technology development and demonstration in the ITD. It is expected that a part (dedicated task) of the activities will be performed by COMOTI through this proposal. The LP turbine detailed design phase will be completed with outcome of AIRSEAL project consolidated with INFRASEAL infrastructure (Technology Readiness Levels TRL 5) in order to launch the phase for components manufacturing. The manufacturing of the parts needed for the ground engine demonstrator (TRL 6) will start. Further design studies will be conducted to improve the gas turbine components. The goals are to validate a 15% reduction in CO2 compared to 2000 baseline.
The existing experimental research infrastructure, in COMOTI facilities, consists of an integrated thermo-gas-dynamic complex for the study and the experimentation of liquid, gas, biomass or biomass derivatives (bio-fuels) fuel combustion, heat transfer, thermal resisting coating, and industrial or aircraft micro gas turbine engines using liquid, gas or biomass (bio-fuels) fuels. The thermo-gas-dynamic complex, however, must be assisted during experimentation by an external air supply station, not belonging to COMOTI and not easily available. The own COMOTI facilities is able to provide air pressure and air mass flow rate by the air source compressor up to 21 bars and 0.35 kg/s at 20oC. The air which feeds the experimental line passes first through an air dryer (dehumidifier) and after this is stored up in a buffer tank followed by a succession of plug valves and control butterfly valves (electrical or electropneumatic), which are centrally controlled. The temperature adjustment up to 700°C is assured with a 192 kW electric heater Inline OSRAM SYLVANIA, by ventilation of the climatic room, with small air mass flows, which will ensure the uniformity of temperature, the process being monitored and computer controlled.
The upgraded air supply line can provide mass flow rates up to 10 kg/s, pressures up to 50 bar, and air temperatures up to 350 oC. The air line can be equipped with a combustor chamber which can be fuelled either by natural gas, or by liquid fuel, able to raise the working fluid temperature up to 800 oC. It is important to note that if the above mentioned combustors will be used to heat up the fluid to the required temperature (up to 800°C), the working fluid is not pure air, but a mixture of flue gas and air.
For the experimental study of labyrinth seal with height mass flow rates, the capabilities of the experimental research infrastructure will be expanded by an upgrade of the existing experimental facility, by designing, building and commissioning the following facilities (Fig.4):
• Test rig for experimental measurement, equipped with air and fuel lines, and with independent command and control chambers;
• Air supply station composed by two lines (compressor and centrifugal air blower) capable to provide a maximum exhaust pressure of 50 bar, and a mass flow rate of 10 kg/s, at a maximum temperature of 185 oC (the maximum pressure and mass flow rate will not be reached simultaneously);
• Air cooling tower to control the temperature of the supplied air;
• Air tank to store the high pressure air supplied by the air supply facility for the purpose of optimizing the energy consumption during the experimentation programs, and to boost the mass flow rate and air flow capabilities of the experimental test rigs for limited periods of time.
• Air heater station included a combustor chamber capable to provide air at 800oC.
According to the budget limits at the project implementation time an expansion in two steps can be take into account (first step - first line, second step - second line). A schematic diagram of proposed facilities for rotating labyrinth seals characterization is presented in Fig.4.
Fig. 4 Schematic view of INFRASEAL proposed facilities for rotating labyrinth seals characterization
The targeted infrastructure will be instrumented by a number of sensors for static and total pressure, static and total temperature, and wall metal temperature. The existing measurement equipment consists in temperature and pressure probes and sensors, temperature resisting rakes, thermo-resistors, Venturi flow meters, as well as advanced measurement equipment will be used for the determination of the instantaneous three-dimensional flow velocity field (Particle Image Velocimetry - PIV), the mean temperature field (Rayleigh thermometry), or the NOx concentration field (Laser Induced Fluorescence - LIF).
This research infrastructure will be expanded in the project through the acquisition and commissioning of new independent research and experimentation installations, machines, equipment and instruments, dedicated to large air flow characterization and advanced combustor chamber studies:
• High speed pressure and temperature measurement system, including probes, transducers, dynamic calibration systems, and connection to the test rig central computer;
• High precision air and fuel (liquid and gaseous) flow rate measurement equipment for high temperatures and pressures;
• Upgrade of the existing LASER PIV instantaneous velocity measurement system for tomography measurements in a three-dimensional volume and for high and very high speed velocity flows, including the flow seeding system;
• Upgrade of the LASER PLIF instantaneous free radicals concentrations in turbulent air flow measurement system for tomography measurements in a three-dimensional volume, and temperature calibration by RAMAN spectroscopy;
• Schlieren high speed flow visualization system, high speed video camera and boroscopes for visible and ultraviolet light;
• High frequency hot wire anemometry system for the measurement of instantaneous velocities;
• Infrared thermo-vision system;
• Measurement systems for high and low frequency force and displacement and vibrations,;
• High precision, automated, command and control systems for flow direction air and probe positioning in the experimental field;
• High speed, multi - channel data acquisition system;
• Acoustic monitoring and noise damping systems;
• Command and control software for the experimental facility and data analysis software for the analysis of experimental data.
A General view of existing and proposed facilities for rotating labyrinth seals characterization is presented in Fig.5.
• High precision air and fuel (liquid and gaseous) flow rate measurement equipment for high temperatures and pressures;
• Upgrade of the existing LASER PIV instantaneous velocity measurement system for tomography measurements in a three-dimensional volume and for high and very high speed velocity flows, including the flow seeding system;
• Upgrade of the LASER PLIF instantaneous free radicals concentrations in turbulent air flow measurement system for tomography measurements in a three-dimensional volume, and temperature calibration by RAMAN spectroscopy;
• Schlieren high speed flow visualization system, high speed video camera and boroscopes for visible and ultraviolet light;
• High frequency hot wire anemometry system for the measurement of instantaneous velocities;
• Infrared thermo-vision system;
• Measurement systems for high and low frequency force and displacement and vibrations,;
• High precision, automated, command and control systems for flow direction air and probe positioning in the experimental field;
• High speed, multi - channel data acquisition system;
• Acoustic monitoring and noise damping systems;
• Command and control software for the experimental facility and data analysis software for the analysis of experimental data.
A General view of existing and proposed facilities for rotating labyrinth seals characterization is presented in Fig.5.
Fig.5 General view of existing and proposed facilities for rotating labyrinth seals characterization
