Detailed Numerical Characterization of the Suction Side Laminar Separation Bubble for a High-Lift Low Pressure Turbine Blade by Means of RANS and LES

2016 ◽  
Author(s):  
Fabio Bigoni ◽  
Stefano Vagnoli ◽  
Tony Arts ◽  
Tom Verstraete
Keyword(s):  
Large Eddy Simulation ◽  
Separation Bubble ◽  
Suction Side ◽  
Reynolds Numbers ◽  
Laminar Separation Bubble ◽  
High Lift ◽  
Laminar Separation ◽  
Low Pressure Turbine ◽  
Eddy Simulation ◽  
Large Eddy

The scope of this work is to obtain a deep insight of the occurrence, development and evolution of the laminar separation bubble which occurs on the suction side of the high-lift T106-C low pressure turbine blade operated at correct engine Mach and Reynolds numbers. The commercial codes Numeca FINE/Turbo and FINE/Open were used for the numerical investigation of a set of three different Reynolds numbers. Two different CFD approaches, characterized by a progressively increasing level of complexity and detail in the solution, have been employed, starting from a steady state RANS analysis and ending with a Large Eddy Simulation. Particular attention was paid to the study of the open separation occurring at the lowest Reynolds number, for which a Large Eddy Simulation was performed in order to try to correctly capture the involved phenomena and their characteristic frequencies. In addition, the potentialities of the codes employed for the analysis have been assessed.

Metamodel-Assisted Optimization of a High-Lift Low Pressure Turbine Blade

2017 ◽  
Author(s):  
Fabio Bigoni ◽  
Roberto Maffulli ◽  
Tony Arts ◽  
Tom Verstraete
Keyword(s):  
Turbine Blade ◽  
Separation Bubble ◽  
Differential Evolution Algorithm ◽  
Suction Side ◽  
Reynolds Numbers ◽  
Low Pressure ◽  
High Lift ◽  
Laminar Separation ◽  
Low Pressure Turbine ◽  
Kriging Metamodel

The scope of this work is to perform a single-objective optimization of the high-lift and aft-loaded T2 low pressure turbine blade profile previously designed at the von Karman Institute for Fluid Dynamics (VKI). At correct engine Mach and Reynolds numbers and for a uniform inflow at low turbulence level, a laminar separation bubble occurs in the decelerating part of the suction side. The main goal of the optimization is to obtain a high-lift and aft-loaded blade characterized by lower aerodynamic losses with respect to the original profile. The optimization uses a metamodel-assisted Differential Evolution algorithm, with an Ordinary Kriging metamodel performing the low-fidelity evaluations and Numeca FINE/Turbo for the high-fidelity ones. The numerical results relative to the optimized profile are compared with those obtained for the baseline profile, in order to highlight the improvements on the blade aerodynamic performance coming from the optimization process.

Parametric Surveys of the Effects of Wake Passing on High Lift LP Turbine Flows Using LES

2007 ◽  
Author(s):  
K. Tomikawa ◽  
H. Horie ◽  
M. Iida ◽  
C. Arakawa ◽  
Y. Ooba
Keyword(s):  
Separation Bubble ◽  
Suction Side ◽  
Computational Domain ◽  
Low Pressure Turbine ◽  
Eddy Simulation ◽  
Boundary Layer Development ◽  
Unsteady Wake ◽  
Large Eddy ◽  
Lp Turbine ◽  
Wake Passing

In this study, Large Eddy Simulation (LES) was applied to predict the boundary layer development within unsteady wake induced linear turbine cascade of Low Pressure turbine (LPT) blades. In the calculation, unsteady wake was simulated by moving cylindrical bars upstream of the blade. The Multiblock method with a parallel computational algorithm was introduced to use the large computational domain with necessary grid refinement. It was demonstrated that the results were good agreement with experiments, and confirmed that a separation bubble of suction side was suppressed by the incoming wakes. Under the condition of significant effect of compressibility, separation point and reattachment point moved to the rear of the blade. In addition, under the condition of low Reynolds number, loss coefficient showed a tendency depending on Strouhal number.

Computational Study of Flow Characteristics of Thick and Thin Airfoil With Implicit Large-Eddy Simulation at Low Reynolds Number

2011 ◽  
Author(s):  
Ryoji Kojima ◽  
Taku Nonomura ◽  
Akira Oyama ◽  
Kozo Fujii
Keyword(s):  
Reynolds Number ◽  
Separation Bubble ◽  
Separated Flow ◽  
Leading Edge ◽  
Laminar Separation Bubble ◽  
Laminar Separation ◽  
Eddy Simulation ◽  
Naca0012 Airfoil ◽  
Large Eddy ◽  
Implicit Large Eddy Simulation

The flow fields around NACA0012 and NACA0002 at Reynolds number of 23,000, and their aerodynamic characteristics are analyzed. Computations are conducted with implicit large-eddy simulation solver and Reynolds-averaged-Navier-Stokes solver. Around this Reynolds number, the flow over an airfoil separates, transits and reattaches, resulting in generation of a laminar separation bubble at angle of attack in the range of certain degrees. Over a NACA0012 airfoil a separation point moves toward its leading edge with increasing angle of attack, and a separated flow may transit to create a short bubble. On the other hand, over a NACA0002 airfoil a separation point is kept at its leading edge, and a separated flow may transit to create a long bubble. Moreover, there appears nonlinearity in lift curve for NACA0012 airfoil, but does not appear in that for NACA0002 in spite of existence of a laminar separation bubble.

Effects of incidence angle on a low-pressure turbine blade boundary layer evolution through large eddy simulation

2018 ◽  
Vol 232 (6) ◽  
pp. 722-734 ◽  
Author(s):  
Yunfei Wang ◽  
Xiuming Sui ◽  
Kai Zhang ◽  
Xiaorong Xiang ◽  
Qingjun Zhao
Keyword(s):  
Boundary Layer ◽  
Large Eddy Simulation ◽  
Coherent Structures ◽  
Separation Bubble ◽  
Incidence Angle ◽  
Leading Edge ◽  
Pressure Side ◽  
Low Pressure Turbine ◽  
Eddy Simulation ◽  
Large Eddy

The evolution mechanism of the boundary layer and coherent structures in a low-pressure turbine blade is discussed. Five different incidence angles over the T106A blade for a Mach number Ma = 0.404 and Reynolds number Re = 0.6 × 105 (based on the axial chord and outlet velocity) are performed using large eddy simulation method. The calculation results at +7.8 incidence angle are agreed well with the experimental and direct numerical simulation data. The influence of the incidence angle on the flow field is mainly shown at the front of the suction side and pressure side. As the incidence angle changes from positive to negative, the separation bubble near the leading edge disappears and the blade loading decreases gradually. When the incidence angle reduces to −5°, separation bubble appears near the leading edge of the pressure side. At the case of incidence angle equaling −10°, the length of time-averaged separation bubble on the pressure side grows to 39% axial chord and the evolution process of the coherent structures is extremely complex. The spanwise vortexes roll up near the leading edge and gradually evolve into streamwise vortexes. High-energy fluid in the main flow was driven to near-wall zone by the rotating effect of streamwise vortexes, which increases the fluid momentum inside the boundary layer. The streamwise vortexes are stretched by the strong acceleration of the flow until they transport to the trailing edge.

Large-Eddy Simulation of Transition in a Separation Bubble

2005 ◽  
Author(s):  
Stephen K. Roberts ◽  
Metin I. Yaras
Keyword(s):  
Large Eddy Simulation ◽  
Separation Bubble ◽  
Suction Side ◽  
Transition Process ◽  
Numerical Dissipation ◽  
Free Stream Turbulence ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Scale Turbulence ◽  
Turbine Airfoils

In this paper, large-eddy simulation of the transition process in a separation bubble is compared to experimental results. The measurements and simulations are conducted under low free-stream turbulence conditions over a flat plate with a streamwise pressure distribution typical of those encountered on the suction side of turbine airfoils. The computational grid is sufficiently refined that the effects of sub-grid scale turbulence are adequately represented by the numerical dissipation of the computational algorithm. The large-eddy simulations are shown to accurately capture the transition process in the separated shear layer. The results of these simulations are used to gain further insight into the breakdown mechanisms in transitioning separation bubbles.

Large Eddy Simulation of Boundary Layer Separation and Reattachment in a LPT Blade at Different Incidence Angles

2015 ◽  
Author(s):  
Yunfei Wang ◽  
Huaping Liu ◽  
Yanping Song ◽  
Fu Chen
Keyword(s):  
Boundary Layer ◽  
Large Eddy Simulation ◽  
Separation Bubble ◽  
Incidence Angle ◽  
Leading Edge ◽  
Suction Side ◽  
Boundary Layer Separation ◽  
Reattachment Point ◽  
Eddy Simulation ◽  
Large Eddy

In order to predict the phenomenon of laminar flow separation, transition and reattachment in a high-lift low-pressure turbine (LPT), a self-developed large eddy simulation program to solve three dimensional compressible N-S equations was used to simulate the flow structures in T106A LPT blade passage. The outlet Mach number is 0.4 and the Reynolds number is 1.1×105 based on the exit isentropic velocity and the axial chord. The distributions of the time-averaged static pressure coefficient, kinetic loss coefficient and wall shear stress on the blade surface at +7.8° incidence angle agree well with the results of experiment and direct numerical simulation (DNS). The locations of laminar separation and reattachment point occur around 83.6% and 97% axial chord respectively. The evolutionary process of spanwise vorticity and large-scale coherent structure near the trailing edge on the suction side in one period indicates that the two-dimensional shear layer is gradually unstable as a result of spanwise fluctuation and Kelvin-Helmholtz (K-H) instability. The boundary layer separates from the suction surface and the hairpin vortex appears in succession, which leads to transition to turbulence. Analysis of the incidence angle effect on the boundary layer separation point as well as separation bubble scale was also performed. A small scale separation bubble exists around the leading edge at positive incidences. As the incidence angle changes from positive to negative, the separation bubble near the leading edge disappears and the boundary layer thickness reduces gradually. The separation point at the rear part of suction side moves downstream, yet the reattachment point barely changes. The Reynolds stress and turbulent kinetic energy profiles change dramatically at zero and positive incidence. This illustrates that the incidence angle has great influence on the development of the boundary layer and the flow field structures.

Large-Eddy Simulation of Transition in a Separation Bubble

2005 ◽  
Vol 128 (2) ◽  
pp. 232-238 ◽  
Author(s):  
Stephen K. Roberts ◽  
Metin I. Yaras
Keyword(s):  
Large Eddy Simulation ◽  
Separation Bubble ◽  
Suction Side ◽  
Transition Process ◽  
Computational Grid ◽  
Eddy Simulation ◽  
Separated Shear Layer ◽  
Large Eddy ◽  
Turbine Airfoils ◽  
Insight Into

In this paper, large-eddy simulation of the transition process in a separation bubble is compared to experimental results. The measurements and simulations are conducted under low freestream turbulence conditions over a flat plate with a streamwise pressure distribution typical of those encountered on the suction side of turbine airfoils. The computational grid is refined to the extent that the simulation qualifies as a “coarse” direct numerical simulation. The simulations are shown to accurately capture the transition process in the separated shear layer. The results of these simulations are used to gain further insight into the breakdown mechanisms in transitioning separation bubbles.

Large Eddy Simulation of Secondary Flows in an Ultra-High Lift Low Pressure Turbine Cascade at Various Inlet Incidences

2020 ◽  
Vol 37 (2) ◽  
pp. 195-207
Author(s):  
Site Hu ◽  
Chao Zhou ◽  
Shiyi Chen
Keyword(s):  
Large Eddy Simulation ◽  
Engine Performance ◽  
Low Pressure ◽  
Secondary Flows ◽  
Turbine Cascade ◽  
High Lift ◽  
Blade Loading ◽  
Low Pressure Turbine ◽  
Eddy Simulation ◽  
Large Eddy

AbstractIncreasing the blade loading of a low pressure turbine blade decreases the number of blades, thus improving the aero-engine performance in terms of the weight and manufacture cost. Many studies focused on the blade-to-blade flow field of ultra-high lift low pressure turbines. The secondary flows of ultra-high lift low pressure turbines received much less attention. This paper investigates the secondary flows in an ultra-high lift low pressure turbine cascade T106C by large eddy simulation at a Reynolds number of 100,000. Both time-averaged and instantaneous flow fields of this ultra-high lift low pressure turbine are presented. To understand the effects of the inlet angle, five incidences of ‒10°, ‒5°, 0, +5° and +10° are investigated. The case at the design incidence is analyzed first. Detailed data is used to illustrate the how the fluids in boundary layers develops into secondary flows. Then, the cases with different inlet incidences are discussed. The aerodynamic performances are compared. The effect of blade loading on the vortex structures is investigated. The horseshoe vortex, passage vortex and the suction side corner vortex are very sensitive to the loading of the front part of the blade.

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