This paper describes the transport and the interaction of pulsating entropy  
  waves generated by combustor burners within a high pressure turbine stage for  
  aeronautical application. Experiments and Computational Fluid Dynamics (CFD)  
  simulations were carried out in the context of the European Research Project  
  RECORD.  
Experimental campaigns considering burner-representative temperature  
  fluctuations injected upstream of an un-cooled high-pressure gas turbine  
  stage have been performed in the high-speed closed-loop test-rig of the Fluid  
  Machine Laboratory (LFM) of Politecnico di Milano (Italy). The turbine  
  geometry is representative of a transonic high pressure gas turbine stage.  
  The pulsating entropy waves are injected at the stage inlet in streamwise  
  direction featuring a 7% over-temperature with respect to the main flow in a  
  frequency range 30-90 Hz. Four different azimuthal positions of the entropy  
  wave generators with respect to the stator leading edges were tested, in all  
  cases inject ed at 75% of the blade span.  
Detailed time-resolved temperature measurements (in the range of 0-200 Hz)  
  upstream and downstream of the stage, as well as in the stator-rotor axial  
  gap were performed. Downstream of the rotor, phase resolved aerodynamic  
  measurements (in the frequency range of 0-100 kHz) were performed as well.  
  Time-accurate CFD simulations with and without entropy fluctuations imposed  
  at the stage inlet were performed with the TRAF code, developed by the  
  University of Florence. A numerical post-processing procedure, based on the  
  DFT (Discrete Fourier Transform) of the conservative variables as been implemented to  
  extract the low frequency content connected to the entropy fluctuations filtering  
  the higher frequencies due, for instance, to the rotor/stator interaction. This  
  approach numerically replicates the experimental temperature acquisition  
  strategy, allowing a direct comparison between numerical and experimental  
  temperature fluctuations.  
Measurements highlighted a significant attenuation of the entropy wave spot  
  throughout their transport within the stator channel and their interaction  
  with the rotor blade rows, highly depending on their injection azimuthal  
  position. Downstream of the rotor, the entropy waves are spread over the  
  pitch and undergo a migration in the spanwise direction strongly dependent on  
  the interaction with the secondary flows.  
Simulations show an overall good agreement with the experiments on the  
  measurement traverses, especially at the stage outlet and allow for explaining  
  with a high level of detail the complex interaction phenomena occurring within  
  the stage. By exploiting the combination of experiments and simulations, the  
  aerodynamic and thermal implications of the temperature fluctuation injected  
  upstream of the stage were properly assessed, thus allowing suggest useful  
  information to the designer.    
The comparison with the experiments confirms the accuracy of the CFD method to  
  solve the periodic, but characterized by a low frequency content event,  
  associated to the entropy wave fluctuation.

 


Computational and Experimental Study of the Unsteady Convection of Entropy Waves Within a High Pressure Turbine Stage

Division / Sponsor:
International Gas Turbine Institute (IGTI)

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2020/volume/84058

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