DES study of blade trailing edge cutback cooling performance with various lip thicknesses

Abstract

Highlights Detached-eddy simulation of the mixing process between mainstream flow and coolant;  Effects of various t/H ratios on blade trailing-edge cutback cooling performance;  Vortex shedding behind the lip plays an important role in near wall cooling efficiency;  Discharge coefficient and adiabatic film-cooling effectiveness agree with experiment;  Thermal mixing has been greatly intensified with the increase of the t/H ratio. ABSTRACTThree-dimensional detached-eddy simulation (DES) study has been carried out to evaluate the cooling performance of a trailing-edge cutback turbine blade with various lip thickness to slot height ratios (t/H). By adopting the shear-stress transport (SST) k-ω turbulence model, the numerical investigations were performed at two successive steps: first, to validate simulation results from an existing cutback turbine blade model with staggered circular pin-fins arrays inside the cooling passage against experimental measurements and other available numerical predictions; second, to understand the effects of the lip thickness to the slot height ratio on the blade trailing-edge cooling performance. It was found from the model validations that at two moderate blowing ratios of 0.5 and 1.1, DES predicted film cooling effectiveness are in very good agreement with experimental data. Further comparisons of four various t/H ratios (t/H = 0.25, 0.5, 1.0, 1.5) have revealed that the thermal mixing process between the 'cold' coolant gas and the 'hot' mainstream flow in the near wake region of the exit slot has been greatly intensified with the increase of the t/H ratio. As a result, it causes a rapid decay of the adiabatic film cooling effectiveness downstream of the blade trailing-edge. The observed vortex shedding and its characteristics in the near wake region are found to play an important role in determining the dynamic process of the 'cold' and the 'warm' airflow mixing, which in turn have significant influences on the prediction accuracy of the near-wall heat transfer performance. As the four t/H ratio increases from 0.25 to 1.5, DES predicts the decrease of main shedding frequencies as f s = 3.69, 3.2, 2.21, and 1.49 kHz, corresponding to Strouhal numbers S t = 0.15, 0.20, 0.23, and 0.22, respectively. These results are in good agreement with available experimental measurements.

Numerical Study of the Axial Gap and Hot Streak Effects on Thermal and Flow Characteristics in Two-Stage High Pressure Gas Turbine

“…The unsteady RANS model used in this study has a low computational cost; however, it has the drawback of being unable to precisely predict vortices and flow separation phenomena that occur around the tips and walls. DES is more accurate; however, it has a high computational cost and previous studies using DES have mostly focused on the local flow phenomena rather than full blade simulations [25][26][27]. With significant advances in computational resources, it is expected that DES or LES will soon be used to accurately predict the complex unsteady flow physics near the tips and walls within full blade simulations.…”

Studi Eksperimental dan Simulasi Numerik Karakteristik Aerodinamika Airfoil NACA 4412

“…Strategi ini dimaksudkan untuk mendapatkan nilai Δy+ hingga 17,2 di daerah sekitar dinding airfoil sehingga simulasi numerik menghasilkan keakuratan tinggi. Tingkat kehalusan mesh di sekitar dinding airfoil memainkan peran penting terhadap keberhasilan simulasi sebagaimana pernah diterapkan pada kasus yang lain [4] [13].…”

Detached-Eddy Simulation of Trailing-Edge (TE) Cutback Turbine Blade Cooling

“…Numerical study considers an experimental configuration investigated by Martini et al [10,20]. The computational domain includes main hot gas domain of stream wise , as published by Effendy et al [21]. The coolant passage contains five rows of staggered-array cylindrical pins located at the coolant flow region.…”

“…The grid refinement studies consider three successive meshes of the baseline domain from coarse to fine at a fixed-wall wall temperature (T w ) of 325 K, as published by Effendy et al [21]. The aim was to assess the adiabatic film-cooling effectiveness for three types of meshes, with considering DES simulation at lowand-high blowing ratios (M = 0.5 and 1.1), in comparison with the experimental data reported by Martini et al [10] and Horbach et al [26].…”

“…Recently, Effendy et al [21], demonstrated the capability of DES on the prediction of the cooling performance of a trailing edge cutback turbine blade cooling with various lip-thicknesses to slot height ratios (t/H) referring to the work of Martini et al [10,20]. The DES study was based on the shear-stress transport (SST)   k turbulence model in order to simulate the dynamic flow interaction between internal coolant and mainstream flow.…”