Locations for on-blade temperature sensors

Sensatek conducted a study on potential locations to place sensors directly on gas turbine blades from using high performance computers equipped with ANSYS Structural and Fluids Suite. Thus, in order to get an estimate of blade surface temperatures under operation, Computational Fluid Dynamics (CFD)models were created. Utilizing CFD models of the blade under operating conditions, hotspots on the blade surface were identified. A steady-state Reynolds Averaged Navier-Stokes, Conjugate Heat Transfer (CHT) analysis of a stationary blade without internal cooling was undertaken in ANSYS. Using a CHT analysis, blade metal surface temperatures and pressure were obtained. This helped us identify potential temperature sensor locations and the pressures at those spots. The temperature & pressure fields obtained from the CHT analysis was then used as our input load for a structural analysis of the blade. The structural analysis of the blade was conducted to obtain stress and deformation of the blade at the potential sensor locations. Figure below shows the temperature distribution on the pressure side of the blade surface respectively for the CHT analysis and the local hot spot designated as 1.

 

 

From Figure above, we can see that a local maximum temperature occurs at the leading edge of the blade close to the hub. This can be attributed to the sharp gradient of blade twist at the leading edge near the hub. Flow stagnation is observed at this edge as well which is also a cause for the localized maximum. There are cooler regions near the trailing edge of the blade since there is rapid acceleration of the fluid in that region. Figure above shows the surface temperature distribution on the surface of the blade.

 

 

From figures above we can observe the local hot spots & areas of high temperature gradients. This aids in identifying potential locations for sensor placement. Knowledge of temperature in the high temperature gradient areas helps us identify locations of higher stress concentration. This can be implemented inblade-lifing models to give a much accurate prediction of blade life and fatigue. Four potential locations have been identified and marked on figures above ; two each on the suction and pressure side. After the 4 potential locations for sensor placement were identified, a stress analysis was conducted by importing the aero-thermal loads from the CHT analysis to identify the stresses that sensor would be exposed to.