Experimental Study of Oscillating Freestream Effect on the Spatiotemporal Distributions of Leading-Edge Film Cooling

2020 ◽  
Vol 143 (1) ◽  
Author(s):  
Hongyi Shao ◽  
Mohamed Qenawy ◽  
Tianlun Zhang ◽  
Di Peng ◽  
Yingzheng Liu ◽  
...  
Keyword(s):  
Experimental Study ◽  
Strouhal Number ◽  
Film Cooling ◽  
Turbine Blades ◽  
Leading Edge ◽  
Fast Response ◽  
Frame Rate ◽  
Cooling Effectiveness ◽  
Oscillation Effect ◽  
Film Cooling Effectiveness

Abstract An experimental study was conducted to investigate the influence of mainstream oscillations on spatio-temporal variation of leading-edge film cooling effectiveness. The investigation utilized fast-response pressure-sensitive paint (Fast-PSP) technique at high frame rate. During the experiment, coolant (i.e., CO2, DR = 1.53) was discharged into three rows of cylindrical holes. Various blowing ratios (i.e., M = 0.50, 0.75, 1.00, and 1.50) were tested under the steady (i.e., f = 0 Hz) and oscillating (i.e., f = 7 Hz and 25 Hz) conditions. The measured instantaneous effectiveness was analyzed in terms of time-averaged and phase-averaged results. The results revealed that the mainstream oscillation, consisting of simultaneous pressure and velocity oscillation, significantly influences the behavior of the film cooling effectiveness. The time-averaged effectiveness significantly decreased at high oscillating frequency (i.e., 13.0–19.8% reduction at M = 0.50, f = 25 Hz compared with f = 0 Hz), especially at low blowing ratios (i.e., M = 0.50 and 0.75). The phase-averaged results captured significant decay in the film distributions associated with backflow caused by negative pressure gradients in coolant holes at certain phases. However, the mainstream oscillation effect was relatively insignificant at high blowing ratios (i.e., M = 1.00 and 1.50), which revealed the robustness of coolant coverage at low coolant Strouhal number (i.e., high blowing ratio) under the same oscillating frequency. Furthermore, the unsteady coolant intermittency showed highly unstable film coverage at high coolant Strouhal number. The coolant decay associated with backflow at high coolant Strouhal number should be considered by the gas-turbine designers in order to improve the lifecycle of turbine blades.

Assessment of URANS and DES for Prediction of Leading Edge Film Cooling

2011 ◽  
Vol 134 (3) ◽  
Author(s):  
Toshihiko Takahashi ◽  
Ken-ichi Funazaki ◽  
Hamidon Bin Salleh ◽  
Eiji Sakai ◽  
Kazunori Watanabe
Keyword(s):  
Turbulence Model ◽  
Film Cooling ◽  
Turbulence Modeling ◽  
Turbine Blades ◽  
Leading Edge ◽  
Vortex Structures ◽  
Temperature Fields ◽  
Detached Eddy Simulation ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness

This paper describes the assessment of CFD simulations for the film cooling on the blade leading edge with circular cooling holes in order to contribute durability assessment of the turbine blades. Unsteady RANS applying a k-ε-v2-f turbulence model and the Spalart and Allmaras turbulence model and detached-eddy simulation (DES) based on the Spalart and Allmaras turbulence model are addressed to solve thermal convection. The CFD calculations were conducted by simulating a semicircular model in the wind tunnel experiments. The DES and also the k-ε-v2-f model evaluate explicitly the unsteady fluctuation of local temperature by the vortex structures, so that the predicted film cooling effectiveness is comparatively in agreement with the measurements. On the other hand, the predicted temperature fields by the Spalart and Allmaras model are less diffusive than the DES and the k-ε-v2-f model. In the present turbulence modeling, the DES only predicts the penetration of main flow into the film cooling hole but the Spalart and Allmaras model is not able to evaluate the unsteadiness and the vortex structures clearly, and overpredict film cooling effectiveness on the partial surface.

Assessment of Steady State PSP and Transient Ir Measurement Techniques for Leading Edge Film Cooling

2005 ◽  
Author(s):  
Zhihong Gao ◽  
Lesley M. Wright ◽  
Je-Chin Han
Keyword(s):  
Heat Transfer ◽  
Steady State ◽  
Film Cooling ◽  
Measurement Techniques ◽  
Turbine Blades ◽  
Leading Edge ◽  
Cooling Effectiveness ◽  
Stagnation Line ◽  
Film Cooling Effectiveness ◽  
Film Cooling Holes

Film cooling is commonly used on the leading edge of turbine blades to protect the blade surface from hot mainstream gases in the turbine. Obtaining detailed film cooling effectiveness distributions on the leading edge can be challenging. This paper considers two measurement techniques which can be applied to the leading edge (modeled by a cylinder) to obtain detailed distributions of the film effectiveness. A steady state pressure sensitive paint (PSP) technique and a transient infrared (IR) thermography technique are used to obtain detailed film cooling effectiveness distributions on the cylinder. The cylinder, 7.62 cm in diameter, is placed in a low speed wind tunnel, with the mainstream flow having a Reynolds number of 100,900 (based on the cylinder diameter). The cylinder has two rows of film cooling holes located at ±15° from the cylinder’s stagnation line. The pitch-to-diameter ratio of the film holes is 4, and holes are inclined 30° in spanwise direction. PSP continues to show promise for film cooling effectiveness measurements. Detailed distributions can be obtained near the film cooling holes because this technique relies on mass transfer rather than heat transfer. In order to reduce the error caused by conduction in heat transfer experiments, transient measurement techniques are favorable. Transient IR measurements are taken, and film cooling effectiveness is determined on the cylinder’s surface. Although the effect of conduction is reduced with the transient IR technique (compared to a steady state heat transfer experiment), heat conduction through the cylinder has not been eliminated (or even minimized). Without correction, the results obtained from transient heat transfer experiments must be used cautiously. For this reason, PSP is developing a niche within the gas turbine community for detailed film cooling effectiveness measurements.

Assessment of URANS and DES for Prediction of Leading Edge Film Cooling

2010 ◽  
Author(s):  
Toshihiko Takahashi ◽  
Ken-ich Funazaki ◽  
Hamidon Bin Salleh ◽  
Eiji Sakai ◽  
Kazunori Watanabe
Keyword(s):  
Turbulence Model ◽  
Film Cooling ◽  
Turbine Blades ◽  
Leading Edge ◽  
Vortex Structures ◽  
Temperature Fields ◽  
Detached Eddy Simulation ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Circular Model

This paper describes assessment of CFD simulations for the film-cooling on the blade leading edge with circular cooling holes in order to contribute durability assessment of the turbine blades. Unsteady RANS (URANS) applying a k–ε–v2–f turbulence model and the Spallart and Allmaras turbulence model, and Detached-Eddy Simulation (DES) based on the Spallart and Allmaras turbulence model are addressed to solve thermal convection. The CFD calculations were conducted by simulating a semi-circular model in the wind tunnel experiments. The DES and also the k–ε–v2–f model evaluate explicitly unsteady fluctuation of local temperature by the vortex structures, so that the predicted film cooling effectiveness comparatively in agreement with measurements. On the other hand, the predicted temperature fields by the Spallart and Allmaras model are less diffusive than the DES and the k–ε–v2–f model. In the present turbulence modeling, the DES only predicts penetration of main flow into the film cooling hole, but the Spallart and Allmaras model is not able to evaluate the unsteadiness and the vortex structures clearly, and over-predict film cooling effectiveness on the partial surface.

Aerothermal Effect of Cavity Welding Beads on a Transonic Squealer Tip

2020 ◽  
Author(s):  
Joao Vieira ◽  
John Coull ◽  
Peter Ireland ◽  
Eduardo Romero
Keyword(s):  
High Pressure ◽  
Film Cooling ◽  
Turbine Blades ◽  
Reynolds Numbers ◽  
High Pressure Turbine ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Aerodynamic Loss ◽  
Blade Tip ◽  
Mass Flow Rates

Abstract High pressure turbine blade tips are critical for gas turbine performance and are sensitive to small geometric variations. For this reason, it is increasingly important for experiments and simulations to consider real geometry features. One commonly absent detail is the presence of welding beads on the cavity of the blade tip, which are an inherent by-product of the blade manufacturing process. This paper therefore investigates how such welds affect the Nusselt number, film cooling effectiveness and aerodynamic performance. Measurements are performed on a linear cascade of high pressure turbine blades at engine realistic Mach and Reynolds numbers. Two cooled blade tip geometries were tested: a baseline squealer geometry without welding beads, and a case with representative welding beads added to the tip cavity. Combinations of two tip gaps and several coolant mass flow rates were analysed. Pressure sensitive paint was used to measure the adiabatic film cooling effectiveness on the tip, which is supplemented by heat transfer coefficient measurements obtained via infrared thermography. Drawing from all of this data, it is shown that the weld beads have a generally detrimental impact on thermal performance, but with local variations. Aerodynamic loss measured downstream of the cascade is shown to be largely insensitive to the weld beads.

Numerical Study on the Influence of Trench Width on Film Cooling Characteristics of Double-Wave Trench

2017 ◽  
Author(s):  
Bo-lun Zhang ◽  
Li Zhang ◽  
Hui-ren Zhu ◽  
Jian-sheng Wei ◽  
Zhong-yi Fu
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Film Cooling ◽  
Numerical Study ◽  
Leading Edge ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Blowing Ratio ◽  
Trench Width

Film cooling performance of the double-wave trench was numerically studied to improve the film cooling characteristics. Double-wave trench was formed by changing the leading edge and trailing edge of transverse trench into cosine wave. The film cooling characteristics of transverse trench and double-wave trench were numerically studied using Reynolds Averaged Navier Stokes (RANS) simulations with realizable k-ε turbulence model and enhanced wall treatment. The film cooling effectiveness and heat transfer coefficient of double-wave trench at different trench width (W = 0.8D, 1.4D, 2.1D) conditions are investigated, and the distribution of temperature field and flow field were analyzed. The results show that double-wave trench effectively improves the film cooling effectiveness and the uniformity of jet at the downstream wall of the trench. The span-wise averaged film cooling effectiveness of the double-wave trench model increases 20–63% comparing with that of the transverse trench at high blowing ratio. The anti-counter-rotating vortices which can press the film on near-wall are formed at the downstream wall of the double-wave trench. With the double-wave trench width decreasing, the film cooling effectiveness gradually reduces at the hole center-line region of the downstream trench. With the increase of the blowing ratio, the span-wise averaged heat transfer coefficient increases. The span-wise averaged heat transfer coefficient of the double-wave trench with 0.8D and 2.1D trench width is higher than that of the double-wave trench with 1.4D trench width at the high blowing ratio conditions.

Leading Edge Film Cooling: Computations and Experiments Including Density Effects

1996 ◽  
Author(s):  
Pingfan He ◽  
Dragos Licu ◽  
Martha Salcudean ◽  
Ian S. Gartshore
Keyword(s):  
Experimental Data ◽  
Film Cooling ◽  
Stokes Equations ◽  
Leading Edge ◽  
Variable Density ◽  
Navier Stokes ◽  
Cooling Effectiveness ◽  
Stagnation Line ◽  
Film Cooling Effectiveness ◽  
Blowing Ratio

The effect of varying coolant density on film cooling effectiveness for a turbine blade-model was numerically investigated and compared with experimental data. This model had a semi-circular leading edge with four rows of laterally-inclined film cooling orifices positioned symmetrically about the stagnation line. A curvilinear coordinate-based CFD code was developed and used for the numerical investigation. The code used a domain segmentation strategy in conjunction with general curvilinear grids to model the complex blade configuration. A multigrid method was used to accelerate the convergence rate. The time-averaged, variable-density, Navier-Stokes equations together with the energy or scalar equation were solved. Turbulence closure was attained by the standard k–ε model with a near-wall k model. Either air or CO2 was used as coolant in three cases of injection through single rows and alternatively staggered double raws of holes. Two different blowing rates were investigated in each case and compared with experimental data. The experimental results were obtained using a wind tunnel model, and the mass/heat analogy was used to determine the film cooling effectiveness. The higher density of the carbon dioxide coolant (approximately 1.5 times the density of air) in the isothermal mass injection experiments, was used to simulate the effects of injection of a colder air in the corresponding adiabatic heat transfer situation. Good agreement between calculated and measured film cooling effectiveness was found for low blowing ratio M ≤ 0.5 and the effect of density was not significant. At higher blowing ratio M > 1 the calculations consistently overpredict the measured values of film cooling effectiveness.

Comparison of RANS and DES Modeling Against Measurements of Leading Edge Film Cooling on a First-Stage Vane

2016 ◽  
Author(s):  
S. Ravelli ◽  
G. Barigozzi
Keyword(s):  
Film Cooling ◽  
Guide Vane ◽  
Leading Edge ◽  
Spanwise Direction ◽  
Intensity Level ◽  
Edge Region ◽  
Cooling Effectiveness ◽  
Stagnation Line ◽  
Film Cooling Effectiveness ◽  
Adiabatic Effectiveness

The performance of a showerhead arrangement of film cooling in the leading edge region of a first stage nozzle guide vane was experimentally and numerically evaluated. A six-vane linear cascade was tested at an isentropic exit Mach number of Ma2s = 0.42, with a high inlet turbulence intensity level of 9%. The showerhead cooling scheme consists of four staggered rows of cylindrical holes evenly distributed around the stagnation line, angled at 45° towards the tip. The blowing ratios tested are BR = 2.0, 3.0 and 4.0. Adiabatic film cooling effectiveness distributions on the vane surface around the leading edge region were measured by means of Thermochromic Liquid Crystals technique. Since the experimental contours of adiabatic effectiveness showed that there is no periodicity across the span, the CFD calculations were conducted by simulating the whole vane. Within the RANS framework, the very widely used Realizable k-ε (Rke) and the Shear Stress Transport k-ω (SST) turbulence models were chosen for simulating the effect of the BR on the surface distribution of adiabatic effectiveness. The turbulence model which provided the most accurate steady prediction, i.e. Rke, was selected for running Detached Eddy Simulation at the intermediate value of BR = 3. Fluctuations of the local temperature were computed by DES, due to the vortex structures within the shear layers between the main flow and the coolant jets. Moreover, mixing was enhanced both in the wall-normal and spanwise direction, compared to RANS modeling. DES roughly halved the prediction error of laterally averaged film cooling effectiveness on the suction side of the leading edge. However, neither DES nor RANS provided the expected decay of effectiveness progressing downstream along the pressure side, with 15% overestimation of ηav at s/C =0.2.

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