Numerical Investigation of Single-Row Double-Jet Film Cooling of a Turbine Guide Vane under High-Temperature and High-Pressure Conditions

Single-row double-jet film cooling (DJFC) of a turbine guide vane is numerically investigated in the present study, under a realistic aero-thermal condition. The double-jet units are positioned at specific locations, with 57% axial chord length (Cx) on the suction side or 28% Cx on the pressure side with respect to the leading edge of the guide vane. Three spanwise spacings (Z) in double-jet unit (Z = 0, 0.5d, and 1.0d, here d is the film hole diameter) and four spanwise injection angles (β = 11°, 17°, 23°, and 29°) are considered in the layout design of double jets. The results show that the layout of double jets affects the coupling of adjacent jets and thus subsequently changes the jet-in-crossflow dynamics. Relative to the spanwise injection angle, the spanwise spacing in a double-jet unit is a more important geometric parameter that affects the jet-in-crossflow dynamics in the downstream flowfield. With the increase in the spanwise injection angle and spanwise spacing in the double-jet unit, the film cooling effectiveness is generally improved. On the suction surface, DJFC does not show any benefit on film cooling improvement under smaller blowing ratios. Only under larger blowing ratios does its positive potential for film cooling enhancement start to show. Compared to the suction surface, the positive potential of the DJFC on enhancing film cooling effectiveness behaves more obviously on the pressure surface. In particular, under large blowing ratios, the DJFC plays dual roles in suppressing jet detachment and broadening the coolant jet spread in a spanwise direction. With regard to the DJFC on the suction surface, its main role in film cooling enhancement relies on the improvement of the spanwise film layer coverage on the film-cooled surface.

Effect of pulse injection on film cooling performance: Experimental and numerical investigation

In this paper, the influence of pulsating air on film cooling of a flat plate at different frequencies and blowing ratios are experimentally and numerically investigated. Square wave pulsed flow is generated at four frequencies of 2, 10, 50, and 100 Hz corresponding to Strouhal numbers of 0.00254, 0.0127, 0.0636, and 0.1271, respectively, and at five blowing ratios of 0.5, 1, 1.5, 2.4, and 3. Reynolds-averaged Navier−Stokes equations are resolved to analyze the coolant film effectiveness based on parameters set in the experiments. The [Formula: see text] model used for turbulent modeling. The obtained results showed that the performance of pulsating cooling decreases with increasing of blowing ratio at the same flow as steady state conditions. The difference between numerical and experimental values for the centerline film effectiveness shows good adaptation at the distances of the injection hole downstream. The lift-off of the local jet increased under pulsation. Increasing the pulse frequency increases the overall efficiency of film cooling. The maximum mean centerline pulsating film cooling effectiveness is obtained at Strouhal number of 0.0636 and a blowing ratio of 0.5, and the minimum value is for Strouhal number of 0.00254 and a blowing ratio of 3. For pulsed flow, the maximum discrepancy of the mean centerline film effectiveness between experimental and numerical results was 17.82%.

FILM COOLING EFFECTIVENESS MEASUREMENT OF FAN-SHAPED HOLES MANUFACTURED USING EDM TECHNIQUE

In this study, the influence of geometric factors such as hole diameter (D), length-to-diameter ratio (L/D), injection angle (a), and lateral expansion angle (α) on film cooling effectiveness of holes made using EDM is experimentally investigated. Nine different cooling configurations were tested on a flat plate wind tunnel at various coolant Reynolds number (Rec) and coolant to mainstream blowing ratio (M). The considered flat plate model incorporates engine sized V-shaped holes. EDM reliability is assessed through a hole qualification process, while effectiveness was measured by the Pressure Sensitive Paint (PSP) technique. Results confirm the suitability of EDM for V-shaped hole manufacturing as long as a correct tolerance on α is prescribed. An accurate qualification of hole morphology is also recommended.

Effect of multi-zone effusion cooling on an adiabatic flat plate for gas turbine application

The present study performed a three-dimensional numerical analysis on an adiabatic flat plate with forward injection holes for multi-zone film cooling. The cooling holes were divided into three-zone, and the cold air was supplied from cylindrical holes at a velocity ratio of 0.5 and 1.5 with 30° inclination to the primary flow. The effect of multi-zone arrangement in film cooling effectiveness is studied, and a comparison between two-zone and three-zone arrangement has been made. Results show that the three-zone arrangement helps achieve better film cooling effectiveness than the two-zone arrangement due to the uniform flow of coolant at a higher velocity ratio. It also reduces the mass flow rate of secondary flow by decreasing the number of cylindrical holes in the perforated plate.

Heat transfer and film cooling measurements on aerodynamic geometries relevant for turbomachinery

A measurement technique for recording convective heat transfer coefficient and adiabatic film cooling effectiveness in demanding environments with highly curved surfaces and limited optical access, such as turbomachinery, is presented. Thermography and tailor-made flexible heating foils are used in conjunction with a novel multistep calibration and data reduction method. This method compensates for sensor drift, angle dependence of surface emissivity and window transmissivity, heat flux inhomogeneity, and conductive losses. The 2D infrared images are mapped onto the 3D curved surfaces and overlapped, creating surface maps of heat transfer coefficient and film cooling effectiveness covering areas significantly larger than the window size. The measurement technique’s capability is demonstrated in a sector-cascade test rig of a turbine center frame (TCF), an inherent component of modern two-spool turbofan engines. The horseshoe vortices were found to play a major role for the thermal integrity of turbine center frames, as they lead to a local increase in heat transfer, and at the same instance, to a reduction of film cooling effectiveness. It was also found that the horseshoe vortices lift off from the curved surface at 50% hub length, resulting in a pair of counter-rotating vortices. The measurement technique was validated by comparing the data against flat plate correlations and also by the linear relation between temperature difference and heat flux. This study is complemented with an extensive error and uncertainty analysis. Article highlights This paper presents an accurate measurement technique for heat transfer and film cooling on 3D curved surfaces with limited optical access using flexible tailor-made heating foils, infrared thermography and a high-fidelity multistep calibration process. Graphical abstract