A set of modern equipment for temperature and heat transfer measurements is available in the laboratory. Heat transfer measurement via IR-thermography was first established by Arroyo (2009) and further developed by Rojo et al. (2013, 2014). Different heating/cooling sources are used to achieve the temperature difference between the surface and the flow, such as electric cartridge heaters, water circulation channels, heat foils and radiative heaters.
The primary tool used in the laboratory is the IR-thermography but the liquid crystal thermography and naphthalene sublimation are used as well. A large amount of resistance temperature detectors (RTD) with traceable uncertainty down to 0.02K, thermocouples (TC), miniature thermocouples, cold-wire probes and film probes is available. Corresponding DAQ equipment such as several units of NI-9217, NI-9214 and SCXI-1520 from National Instruments is readily available. The temperature calibrations are reference traceable.
This is the primary method for surface temperature measurements in the laboratory see Fig. 4.13. Heating of the models is realized either by heat foils as in Wang et al. (2013, 2016) or by electrical/water heating systems as in Arroyo (2009) and Rojo et al. (2013, 2014). A recent development is using rapid prototyping for manufacturing a vane with a section of hub and shroud with an embedded water channel system REF TO ETC. The new improved technique reduces uncertainties associated with the wall thickness non-uniformity and thermal conductivity variations. The new method provides substantially reduced manufacturing and instrumentation time at reduced model cost. The IR system used in the laboratory is from Phoenix with a 320 × 256 sensor and a frame rate of 122 Hz at full-frame. In-house developed control and image processing software is used to achieve high accuracy measurements and flexible post-processing. For bigger frame or faster sampling, we have the ability to rent cameras from FLIR.
Calibrator to the left with the Phoenix camera. Rented from FLIR to the right.
Typical results of measurement of the heat transfer coefficient on a vane, hub and shroud (from Arroyo, 2009) is shown in Fig. 4.13-left and a calibrator with Phoenix IR-camera in Fig.4.13-right. Typical IR-camera field of view is illustrated in Fig. 4.14-right. The leading edge of the vane is typically outside of the field of view and the temperature of the leading edge is measured by miniature thermocouples embedded on the surface (Fig. 4.16).
Figure 4.13. Heat transfer coefficient on the vane, hub and shroud from Arroyo, 2009 (left) and a calibrator with Phoenix IR-camera from Rojo, 2014 (right).
The IR camera if often used as for flow visualisation by study the temperature fluctuations on the surface, this is non-intrusive method often used in the wind tunnel testing to detect vortex or transition location. For simpler tests this is done by external heating such as directional light but can be done with dispersed PIV laser or internal heating as well for more advanced testing. Below there is an example from OGV-LPT tunnel to the left where the high temperature fluctuations represent the transition point, and to the right the large scale vortices in a delta wing can be seen in the L2 tunnel.
Liquid Crystal Thermography
In applications where the access for an IR-camera is limited a Liquid Crystal Thermography (LCT) technique is used as an alternative method for surface temperature mapping. Figure 4.15 shows typical LCT images and Nusselt number distributions from a liquid crystal thermography measurement obtained in the CHALMERS’ linear cascade (Wang et al. 2014).
Figure 4.15. Typical LCT images and Nusselt number distributions from liquid crystal thermography measurement (Wang et al. 2014).
This method is described in Jamshidi (2017) for heat transfer measurements in small cooling channels in an electric generator where optical access is not possible without substantially disturbing the flow field. The method was recently upgraded for improved measurement accuracy. An example test piece instrumented for naphthalene sublimation is shown in Fig. 4.16.
Arroyo, C. (2009) Aerothermal Investigation of an Intermediate Turbine Duct, PhD thesis, Chalmers.
Jamshidi, H. (2017) Ventilation of Flow Field Characteristics of a Hydro-Generator Model, PhD thesis, Chalmers.
Rojo, B., Johansson, M., Chernoray V. (2013) Experimental Heat Transfer Study in an Intermediate Turbine Duct. 49TH AIAA/ASME/SAE/ASEE Joint Propulsion Conference.
Rojo, B., Jimenez Sanchez, C., Chernoray, V. (2014) Experimental Heat Transfer Study of Endwall in a Linear Cascade with IR Thermography. EPJ Web of Conferences. Vol. 67.
Shiri A. (2010) Turbulence Measurements in a Natural Convection Boundary Layer and a Swirling Jet, PhD thesis, Chalmers.
Wang, L., Sundén B., Chernoray V., Abrahamsson, H. (2013) Endwall Heat Transfer Measurements of an Outlet Guide Vane at on and off Design Conditions. In Proc. of ASME Turbo Expo 2013: Paper GT2013-95008.
Wang, C. F., Wang, L., Sundén B., Chernoray V., Abrahamsson H. (2014) An Experimental Study of Heat Transfer on an Outlet Guide Vane. In Proc. of ASME Turbo Expo 2014. Paper GT2014-25100. Wang, C. L., Luo,
L., Wang L. Chernoray, V., Sundén B. (2016) Experimental and Numerical Investigation of Outlet Guide Vane and Endwall Heat Transfer with Various Inlet Flow Angles. International Journal of Heat and Mass Transfer. Vol. 95, p. 355-367.
Figure 4.16. Naphthalene casted test piece for heat transfer measurements (left) and a miniature 0.025-mm thermocouple for wall mounting (right).