Profiled End-Wall Design Using an Adjoint Navier-Stokes Solver

2006 ◽  
Author(s):  
Roque Corral ◽  
Fernando Gisbert
Keyword(s):  
Kinetic Energy ◽  
Cost Function ◽  
Unstructured Mesh ◽  
Low Pressure ◽  
Navier Stokes ◽  
Low Pressure Turbine ◽  
Gradient Based ◽  
Parallel Multigrid ◽  
End Wall ◽  
Discrete Formulation

A methodology to minimize blade secondary losses by modifying turbine end-walls is presented. The optimization is addressed using a gradient-based method, where the computation of the gradient is performed using an adjoint code and the secondary kinetic energy is used as a cost function. The adjoint code is implemented on the basis of the discrete formulation of a parallel multigrid unstructured mesh Navier-Stokes solver. The results of the optimization of two end-walls of a low pressure turbine row are shown.

Profiled End Wall Design Using an Adjoint Navier–Stokes Solver

2008 ◽  
Vol 130 (2) ◽  
Author(s):  
Roque Corral ◽  
Fernando Gisbert
Keyword(s):  
Kinetic Energy ◽  
Cost Function ◽  
Unstructured Mesh ◽  
Low Pressure ◽  
Navier Stokes ◽  
Low Pressure Turbine ◽  
Gradient Based ◽  
Parallel Multigrid ◽  
End Wall ◽  
Discrete Formulation

A methodology to minimize blade secondary losses by modifying turbine end walls is presented. The optimization is addressed using a gradient-based method, where the computation of the gradient is performed using an adjoint code and the secondary kinetic energy is used as a cost function. The adjoint code is implemented on the basis of the discrete formulation of a parallel multigrid unstructured mesh Navier–Stokes solver. The results of the optimization of two end walls of a low-pressure turbine row are shown.

scholarly journals Numerical Investigation of Wake Interaction in a Low Pressure Turbine

1998 ◽  
Author(s):  
Frank Eulitz ◽  
Karl Engel
Keyword(s):  
Phenomenological Study ◽  
Separated Flow ◽  
Low Pressure ◽  
Skin Friction Coefficient ◽  
Boundary Layer Transition ◽  
Navier Stokes ◽  
Layer Transition ◽  
Low Pressure Turbine ◽  
Wake Interaction ◽  
Large Fluctuations

A time-accurate Reynolds-averaged Navier-Stokes solver has been extended for a phenomenological study of wake/bladerow interaction in a low pressure turbine near midspan. To qualitatively account for unsteady laminar-turbulent boundary layer transition, a variant of the Abu-Ghanam Shaw transition correlation has been coupled with the Spalart-Allmaras one-equation turbulence model. The method is shown to be capable of capturing separated-flow and wake-induced transition, as well as becalming and relaminarization effects. The model turbine investigated consists of three stator and two rotor rows. Instantaneous Mach number and eddy-viscosity plots are presented to monitor the wake migration and interaction with downstream boundary layers. Especially on the suction sides, very large fluctuations of the skin friction coefficient are observed. Effects of the near and far wakes are identified.

Highly Resolved Large Eddy Simulation Study of Gap Size Effect on Low-Pressure Turbine Stage

2017 ◽  
Vol 140 (2) ◽  
Author(s):  
R. Pichler ◽  
V. Michelassi ◽  
R. Sandberg ◽  
J. Ong
Keyword(s):  
Kinetic Energy ◽  
Cross Sections ◽  
Control Volume ◽  
Leading Edge ◽  
Suction Side ◽  
Low Pressure ◽  
Small Time ◽  
Gap Size ◽  
Low Pressure Turbine ◽  
Large Eddy

Blade-to-blade interactions in a low-pressure turbine (LPT) were investigated using highly resolved compressible large eddy simulations (LESs). For a realistic setup, a stator and rotor configuration with profiles typical of LPTs was used. Simulations were conducted with an in-house solver varying the gap size between stator and rotor from 21.5% to 43% rotor chord. To investigate the effect of the gap size on the prevailing loss mechanisms, a loss breakdown was conducted. It was found that in the large gap (LG) size case, the turbulence kinetic energy (TKE) levels of the stator wake close to the rotor leading edge were only one third of those in the small gap (SG) case, due to the longer distance of constant area mixing. The small time-averaged suction side separation on the blade, found in the LG case, disappeared in the SG calculations, confirming how stronger wakes can keep the boundary layer attached. The higher intensity wake impinging on the blade, however, did not affect the time-averaged losses calculated using the control volume approach of Denton. On the other hand, losses computed by taking cross sections upstream and downstream of the blade revealed a greater distortion loss generated by the stator wakes in the SG case. Despite the suction side separation suppression, the SG case gave higher losses overall due to the incoming wake turbulent kinetic energy amplification along the blade passage.

Experimental and Numerical Investigation of Secondary Flow Structures in an Annular Low Pressure Turbine Cascade Under Periodic Wake Impact—Part 2: Numerical Results

2019 ◽  
Vol 141 (2) ◽  
Author(s):  
Benjamin Winhart ◽  
Martin Sinkwitz ◽  
Andreas Schramm ◽  
David Engelmann ◽  
Francesca di Mare ◽  
...  
Keyword(s):  
Secondary Flow ◽  
Direct Interaction ◽  
Numerical Data ◽  
Horseshoe Vortex ◽  
Low Pressure ◽  
Navier Stokes ◽  
Flow Structures ◽  
Pressure Loss Coefficient ◽  
Low Pressure Turbine ◽  
Numerical Predictions

In this work, we present the results of the numerical investigations of periodic wake–secondary flow interaction carried out on a low pressure turbine (LPT) equipped with modified T106-profile blades. The numerical predictions obtained by means of unsteady Reynolds-averaged Navier–Stokes (URANS) simulations using a k-ω-model have been compared with measurements conducted in the same configuration and showed a good agreement. Based on the verified numerical data, the Q-criterion has been employed to characterize the secondary flow structures and accurately identify their origin. An analysis of the fundamental wake kinematics and the unsteady vortex migration revealed dominant interaction mechanisms such as the circumferential fluctuation of the pressure side horseshoe vortex (HSV) and its direct interaction with the passage vortex (PV) and the concentrated shed vortex (CSV). Finally, a correlation with the total pressure loss coefficient is provided and a link to the incoming wake structures is given.

Implicit Large Eddy Simulation of Low Pressure Turbine Airfoils Using a High Order Navier-Stokes Solver

2019 ◽  
Author(s):  
Marc Bolinches-Gisbert ◽  
Roque Corral ◽  
Fernando Gisbert ◽  
Adrián Sotillo
Keyword(s):  
Large Eddy Simulation ◽  
Low Pressure ◽  
High Order ◽  
Navier Stokes ◽  
Low Pressure Turbine ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Turbine Airfoils ◽  
Implicit Large Eddy Simulation

A Low Pressure Turbine With Profiled End Walls and Purge Flow Operating With a Pressure Side Bubble

2011 ◽  
Author(s):  
P. Jenny ◽  
R. S. Abhari ◽  
M. G. Rose ◽  
M. Brettschneider ◽  
J. Gier
Keyword(s):  
Computational Study ◽  
Leading Edge ◽  
Low Pressure ◽  
Fast Response ◽  
Turbine Rotor ◽  
Operating Point ◽  
Pressure Side ◽  
Low Pressure Turbine ◽  
Purge Flow ◽  
End Wall

This paper presents an experimental and computational study of non-axisymmetric rotor end wall profiling in a low pressure turbine. End wall profiling has been proven to be an effective technique to reduce both turbine blade row losses and the required purge flow. For this work a rotor with profiled end walls on both hub and shroud is considered. The rotor tip and hub end walls have been designed using an automatic numerical optimisation that is implemented in an in-house MTU code. The end wall shape is modified up to the platform leading edge. Several levels of purge flow are considered in order to analyze the combined effects of end wall profiling and purge flow. The non-dimensional parameters match real engine conditions. The 2-sensor Fast Response Aerodynamic Probe (FRAP) technique system developed at ETH Zurich is used in this experimental campaign. Time-resolved measurements of the unsteady pressure, temperature and entropy fields between the rotor and stator blade rows are made. For the operating point under investigation the turbine rotor blades have pressure side separations. The unsteady behavior of the pressure side bubble is studied. Furthermore, the results of unsteady RANS simulations are compared to the measurements and the computations are also used to detail the flow field with particular emphasis on the unsteady purge flow migration and transport mechanisms in the turbine main flow containing a rotor pressure side separation. The profiled end walls show the beneficial effects of improved measured efficiency at this operating point, together with a reduced sensitivity to purge flow.

The Unsteady Development of a Turbulent Wake Through a Downstream Low-Pressure Turbine Blade Passage

2005 ◽  
Vol 127 (2) ◽  
pp. 388-394 ◽  
Author(s):  
R. D. Stieger ◽  
H. P. Hodson
Keyword(s):  
Boundary Layer ◽  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Low Pressure ◽  
Boundary Layer Transition ◽  
Production Mechanism ◽  
Blade Passage ◽  
Low Pressure Turbine ◽  
Blade Row ◽  
Turbulence Production

This paper presents two-dimensional LDA measurements of the convection of a wake through a low-pressure turbine cascade. Previous studies have shown the wake convection to be kinematic, but have not provided details of the turbulent field. The spatial resolution of these measurements has facilitated the calculation of the production of turbulent kinetic energy, and this has revealed a mechanism for turbulence production as the wake convects through the blade row. The measured ensemble-averaged velocity field confirmed the previously reported kinematics of wake convection while the measurements of the turbulence quantities showed the wake fluid to be characterized by elevated levels of turbulent kinetic energy (TKE) and to have an anisotropic structure. Based on the measured mean and turbulence quantities, the production of turbulent kinetic energy was calculated. This highlighted a TKE production mechanism that resulted in increased levels of turbulence over the rear suction surface where boundary-layer transition occurs. The turbulence production mechanism within the blade row was also observed to produce more anisotropic turbulence. Production occurs when the principal stresses within the wake are aligned with the mean strains. This coincides with the maximum distortion of the wake within the blade passage and provides a mechanism for the production of turbulence outside of the boundary layer.

Predicting Transition in Turbomachinery—Part II: Model Validation and Benchmarking

2004 ◽  
Vol 129 (1) ◽  
pp. 14-22 ◽  
Author(s):  
T. J. Praisner ◽  
E. A. Grover ◽  
M. J. Rice ◽  
J. P. Clark
Keyword(s):  
Experimental Testing ◽  
Local Heat Transfer ◽  
Low Pressure ◽  
Boundary Layer Transition ◽  
Transfer Coefficients ◽  
Layer Transition ◽  
Low Pressure Turbine ◽  
Rans Simulations ◽  
Transition Modeling ◽  
End Wall

The ability to predict boundary layer transition locations accurately on turbomachinery airfoils is critical both to evaluate aerodynamic performance and to predict local heat-transfer coefficients with accuracy. Here we report on an effort to include empirical transition models developed in Part I of this report in a Reynolds averaged Navier-Stokes (RANS) solver. To validate the new models, two-dimensional design optimizations utilizing transitional RANS simulations were performed to obtain a pair of low-pressure turbine airfoils with the objective of increasing airfoil loading by 25%. Subsequent experimental testing of the two new airfoils confirmed pre-test predictions of both high and low Reynolds number loss levels. In addition, the accuracy of the new transition modeling capability was benchmarked with a number of legacy cascade and low-pressure turbine (LPT) rig data sets. Good agreement between measured and predicted profile losses was found in both cascade and rig environments. However, use of the transition modeling capability has elucidated deficiencies in typical RANS simulations that are conducted to predict component performance. Efficiency-versus-span comparisons between rig data and multi-stage steady and time-accurate LPT simulations indicate that loss levels in the end wall regions are significantly under predicted. Possible causes for the under-predicted end wall losses are discussed as well as suggestions for future improvements that would make RANS-based transitional simulations more accurate.

Verification of the Vibration Amplitude Prediction of Self-Excited LPT Rotor Blades Using a Fully Coupled Time-Domain Non-Linear Method and Experimental Data

2008 ◽  
Author(s):  
Roque Corral ◽  
Juan Manuel Gallardo
Keyword(s):  
Experimental Data ◽  
Dry Friction ◽  
Vibration Amplitude ◽  
Low Pressure ◽  
Rotor Blades ◽  
Navier Stokes ◽  
Disk Model ◽  
Low Pressure Turbine ◽  
Non Linear ◽  
Fully Coupled

The vibration level of aerodynamically unstable low-pressure-turbine rotor blades has been assessed for the first time using two-different approaches. Both methods assume that the aerodynamic forcing is due solely to the self-excitation of the airfoil and that the vibration amplitude is saturated due to the non-linearity associated to the fir-tree dry friction, which is modeled using a simplified approach. To compensate for the limitations of the friction model several hypotheses need to be done, among them, the geometric similarity of the different configurations and that the aspect ratio of the rotor blades is high. The first approach, which is novel, assumes that the vibration amplitude is small enough and the unsteady aerodynamics associated to the airfoil motion may be computed using a frequency domain linearized Navier-Stokes solver. The vibration amplitude is obtained posing the energy balance between the energy exerted by the most unstable aerodynamic mode and the energy dissipated by dry friction. The second approach time marches simultaneously the Reynolds-Average Navier Stokes equations and a simple mass-spring non-linear model consistent with the mechanical model used in the first approach. This fully coupled non-linear, both in the aerodynamic and structural sides, flutter analysis is considered unique in its kind. It is demonstrated by means of a simplified, but consistent with typical low-pressure-turbine bladed-disk, model that both methods are equivalent. The first approach has been applied to several bladed-disks and the comparison with experimental data is good in overall.

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