Holger Werschnik

Infrared thermography to study endwall cooling and heat transfer in turbine stator vane passages using the auxiliary wall method and comparison to numerical simulations

Experiments using the auxiliary wall method and infrared thermography allow to study film cooling and heat transfer in turbomachinery research with high spatial resolution. Using heater foils and pulse width modulation, an aluminium body is heated to constant wall temperature, controlled by thermocouples. The heat flux is then determined across a low conductivity layer of Ethylene-Tetrafluoroethylene (ETFE), whereby 1-D conduction is assumed. Setting the base body to several quasi-steady state wall temperatures allows to deduce adiabatic wall temperatures and heat transfer coefficients. Given a coolant and main flow with different temperature, cooling effectiveness can be calculated, using a superposition approach. Experiments in the linear cascade test rig of the Institute for Gas Turbines and Aerospace Propulsion have been performed to study the effect of hub side coolant injection on the endwall heat transfer of a turbine stator row. The quality of results is examined through extensive data analysis, accompanied by a numerical simulation of the experiment.

The Impact of Realistic Inlet Swirl in a 1 ½ Stage Axial Turbine

Further improvements of gas turbine design can be expected if realistic turbine inlet conditions are applied. These include discrete swirl cores and hot spots which exit from the combustion chamber. A large scale turbine rig is currently reconfigured at Technische Universitat Darmstadt to analyse the effect of realistic swirl intensity on turbine flow and heat transfer. A comparison is to be made between swirling and axial inflow conditions. The swirl generator causes a recirculation zone inside the combustion chamber. As a result, the total pressure at turbine inlet is reduced at midspan and increased near the end walls. In addition, incidence angles of ±15° occur at hub and casing of the nozzle guide vane (NGV). This swirl and the shape of the pressure profile are typical for modern lean combustion concepts which are relevant to reduce emissions like NOX.During the design of the test rig, computational flow simulations are carried out. Different swirl orientations and clocking positions are investigated in advance. Depending on these parameters, there is a potential of 0.5 % efficiency between the optimal and the worst configuration. Comparing swirling with axial inflow conditions, an efficiency deficit of more than 2 % has been found which is mainly due to the increased turbulence level for swirling flow. In addition, heat transfer through the NGV hub is increased by approximately 20%. This paper aims for understanding the generation of these aerodynamic and thermal losses to allow for their elimination in future engine designs. Therefore, the most complex case of a realistic swirl generator is successively simplified towards a case with axial inflow: Two-dimensional inflow conditions including discrete swirl and loss cores are compared to radial distributions of inflow variables and globally constant values. The influence of swirling inflow, total pressure profile and turbulence level are simulated separately in order to identify their individual impact on aerodynamic and thermal losses.Copyright

Experimental Analysis of the Interaction Between Rim Seal and Main Annulus Flow in a Low Pressure Two Stage Axial Turbine

The spoiling effects of rim seal flow are studied at the Large Scale Turbine Rig (LSTR) at Technische Universitat Darmstadt. Detailed flow field measurements and efficiency measurements were performed for various ingress and egress setups and will be presented in this paper. Efficiency measurements show an efficiency decrease as the rim seal mass flow is increased. Five hole probe measurements upstream and downstream of the second stator row show that an increasing rim seal mass flow leads to an increased pressure loss across the stator, to altered incidence angles and to an intensification of secondary flow structures within the lower 50% span. Static pressure taps at the stator profile primarily show altered aerodynamic loading with increased rim seal air. In addition, the end wall profile pressure was measured at the stator 2 hub. It can be seen that seal air injection causes increased pressure fluctuations on the platform. Temperature measurements with a temperature difference between rim seal and main annulus flow show that rim seal air primarily enters the passage vortex.

The Influence of Combustor Swirl on Pressure Losses and the Propagation of Coolant Flows at the Large Scale Turbine Rig (LSTR)

The aerothermal interaction of the combustor exit flow on the subsequent vane row has been examined at the Large Scale Turbine Rig (LSTR) at Technische Universit¨at Darm-stadt. A baseline configuration with axial and swirling combustor inflow have been studied subsequently. The NGV featured endwall cooling, airfoil film cooling and a trailing edge slot ejection as well as NGV-rotor wheel space purge flow. CO2 is injected for coolant flow tracing and the results are compared to 5HP measurements. The hub side endwall coolant injection is detected to influence the pressure losses in the NGV. It also has an impact on the TE coolant ejection. For swirling combustor inflow, increased NGV pressure losses and increased mixing of RIDN and main flow is observed. An influence of the clocking position of swirler to vane is detected. Additional losses within the NGV stage can be assigned to the swirler by means of flow tracing.

A Large Scale Turbine Test Rig for the Investigation of High Pressure Turbine Aerodynamics and Heat Transfer With Variable Inflow Conditions

Focusing on the experimental analysis of the effect of variable inlet flows on aerodynamics, efficiency and heat transfer of a modern high pressure turbine, the Large Scale Turbine Rig (LSTR) at Technische Universitat Darmstadt has been extensively redesigned.The LSTR is a full annular, rotating low speed turbine test rig carrying a scaled 1.5-stage (NGV1 - Rotor - NGV2) axial high-pressure turbine geometry designed by Rolls-Royce Deutschland to match engine-realistic Reynolds numbers. To simulate real turbine inflow conditions, the LSTR is equipped with a combustor simulator module including exchangeable swirlers. Other inflow conditions include axial or turbulent inflow as well as altered relative positions of swirl cores and NGVs by traversing. To investigate combustor-turbine interaction, the LSTR offers a large variety of optical and physical access ports as well as high flexibility to the application of measurement techniques.An elaborate secondary air system enables the simulation of various cooling air flows. The turbine section is equipped with film-cooled NGVs, a hub side seal air injection between NGVs and rotor, as well as a hub side RIDN cooling air injection module designed to provide realistic turbine flow conditions. Exchangeable hub side RIDN-plates allow for investigation of different coolant injection geometries.Measurement capabilities include 5-hole-probes, Pitot and total temperature rakes, as well as static pressure taps distributed along NGV radial sections and at the hub side passage endwall. The NGV passage flow can be visualized by means of Particle Image Velocimetry (PIV). Hot Wire Anemometry (HWA) will be used for time-resolved measurements of the turbulence level at several positions. The distributions of heat transfer and film cooling effectiveness are acquired using infrared thermography and CO2-gas tracing.Copyright