scholarly journals Local Entropy Generation in Compressible Flow through a High Pressure Turbine with Delayed Detached Eddy Simulation

Entropy ◽  
2017 ◽  
Vol 19 (1) ◽  
pp. 29 ◽  
Author(s):  
Dun Lin ◽  
Xin Yuan ◽  
Xinrong Su
Author(s):  
Dun Lin ◽  
Xinrong Su ◽  
Xin Yuan

In this work, the flows inside the high pressure turbine (HPT) vane and stage are studied with the help of a high-fidelity delayed detached eddy simulation (DDES) code. This work intends to study the fundamental nozzle/blade interaction with special attention paid to the development and transportation of the vane wake vortex. There are two motivations for this work. On the one hand, the high pressure turbine operates at both transonic Mach numbers and high Reynolds numbers, which imposes a great challenge to modern computational fluid dynamics (CFD), especially for scale-resolved simulation methods. An accurate and efficient high-fidelity CFD solver is very important for a thorough understanding of the flow physics and the design of more efficient HPT. On the other hand, the periodic wake vortex shedding is an important origin of turbine losses and unsteadiness. The wake and vortex not only cause losses themselves, but also interact with the shock wave (under transonic working condition), pressure waves, and have a strong impact on the downstream blade surface (affecting boundary layer transition and heat transfer). Built on one of our previous DDES simulations of a HPT vane VKI LS89, this work further investigates the development and length characteristics of the wake vortex, provides explanations of the length characteristics and reveals the transportation of the wake vortex into the downstream rotor passage along with its impact on the downstream aero-thermal performance.


Entropy ◽  
2005 ◽  
Vol 7 (1) ◽  
pp. 38-67 ◽  
Author(s):  
Hüseyin Yapici ◽  
Nesrin Kayatas ◽  
Nafiz Kahraman ◽  
Gamze Bastürk

Author(s):  
Dun Lin ◽  
Xiutao Bian ◽  
Xin Yuan ◽  
Xinrong Su

In this work, the flow inside a high pressure turbine (HPT) stage is studied with the help of a high-fidelity delayed detached eddy simulation (DDES) code. This work intends to study the flow topology in the HPT stage. There are two motivations for this work: On the one hand, high pressure turbines operates at both transonic Mach numbers and high Reynolds numbers, which imposes a challenge to modern computational fluid dynamics (CFD), especially for scale-resolved simulation methods. An accurate and efficient high-fidelity CFD solver is very important for a thorough understanding of the flow physics and the design of higher-efficient HPT. On the other hand, the wake vortex shedding and tip-leakage flow are important origins of turbine losses and unsteadiness. Built on our previous DDES simulations of HPT vane and stage, this work further investigates the flow in a full 3-dimension HPT stage. The flow topology in the HPT stage is delineated by Q-criterion iso-surfaces. The development of the horseshoe vortex and its interaction with induced vortex and wake vortex is discussed. The wake vortex transportation especially its interaction with the rotor horseshoe vortex is investigated. The flow structures in the tip clearance region are also revealed.


Author(s):  
M. Reza H. Sheikhi ◽  
Mehdi Safari ◽  
Hameed Metghalchi

A novel methodology is developed for local entropy generation analysis of turbulent flows using large eddy simulation (LES). The entropy transport equation is introduced in LES. The filtered form of this equation includes the unclosed subgrid scale entropy generation effects. The closure is based on the filtered density function (FDF) methodology, extended to include the transport of entropy. An exact transport equation is derived for the FDF. The unclosed terms in this equation is modeled by considering a system of stochastic differential equations. LES/FDF is employed to simulate a turbulent shear layer involving transport of mass, energy and entropy. The local entropy generation effects are obtained from the FDF and analyzed. It is shown that the dominant contribution to entropy generation in this flow is due to the combined effects of energy transfer by heat interaction and mass diffusion.


2012 ◽  
Vol 134 (4) ◽  
Author(s):  
M. R. H. Sheikhi ◽  
Mehdi Safari ◽  
Hameed Metghalchi

A new methodology is developed for local entropy generation analysis of turbulent flows using large eddy simulation (LES). The entropy transport equation is considered in LES and is solved along with continuity, momentum, and scalar transport equations. The filtered entropy equation includes several unclosed source terms that contribute to entropy generation. The closure is based on the filtered density function (FDF) methodology, extended to include the transport of entropy. An exact transport equation is derived for the FDF. The unclosed terms in this equation are modeled by considering a system of stochastic differential equations (SDEs). The methodology is employed for LES of a turbulent shear layer involving transport of passive chemical species, energy, and entropy. The local entropy generation effects are obtained from the FDF and are analyzed. It is shown that the dominant contribution to entropy generation in this flow is due to combined effects of energy transfer by heat and mass diffusion. The FDF results are assessed by comparing with those obtained by direct numerical simulation (DNS) of the same layer. The FDF predictions show favorable agreements with the DNS data.


Author(s):  
Mehdi Safari

Analysis of local entropy generation is an effective means to investigate sources of efficiency loss in turbulent combustion from the standpoint of the second law of thermodynamics. A methodology, termed the entropy filtered density function (En-FDF), is developed for large eddy simulation (LES) of turbulent reacting flows to include the transport of entropy, which embodies the complete statistical information about entropy variations within the subgrid scale. The modeled En-FDF contains a stochastic differential equation (SDE) for entropy which is solved by a Lagrangian Monte Carlo method. In this study, a numerical study has been done on effectiveness of SDE to model entropy variation using a partially stirred reactor (PaSR). This provides a computationally affordable case to compare different effects of entropy generation source terms and fine tune mixing coefficients. In this equation, turbulent mixing is modeled with Interaction by Exchange with the Mean (IEM). Combustion source terms are provided by direct integration of a GRI3.0 mechanism for methane/air system. Evolution of entropy was calculated from stochastic model and then compared with the one obtained directly by integrating the chemical mechanism. It was shown that results of both calculations have very good agreement versus different mixture fractions.


Author(s):  
Hui Li ◽  
Xiutao Bian ◽  
Xinrong Su ◽  
Xin Yuan

Abstract The complex leakage flow structure in the tip region of unshrouded rotor is a main source of turbine aerodynamic loss. Due to the complex turbulence characteristics of the tip leakage flow, the widely used Reynolds Averaged Navier-Stokes (RANS) approach may fail to accurately predict the multi-scale turbulent flow and the related loss. In order to effectively improve the turbine efficiency, more insights into the turbulence characteristics and the loss mechanism in the tip leakage flow are required. In this work, a Delayed Detached Eddy Simulation (DDES) study is conducted to simulate the flow inside a high pressure turbine blade, with emphasis on the tip region. DDES results are in good agreement with the experiment and the comparison with RANS results verifies the advantages of DDES in resolving finer flow structures of leakage flow, also in capturing the complex turbulence characteristics. The snapshot Proper Orthogonal Decomposition (POD) method is used to extract the dominant flow features. The flow structures and the distribution of Reynolds stress help to reveal the process of leakage flow and its interaction with the secondary flow. Meanwhile, it is found that the separation vortex (SV) forms from leading edge to trailing edge, and the strong interactions between tip leakage vortex (TLV) and passage secondary vortex (PSV) significantly enhance the turbulence intensity. Based on the DDES results, loss analysis of tip leakage flow is conducted based on entropy generation rates. For the leakage flow related loss, the largest local entropy generation rate occurs at 50 % of axial chord, and the interaction between the leakage vortex and up passage vortex promotes the loss generation. To sum up, the current DDES study about the tip leakage flow provides helpful information about the loss generation mechanism and may guide the design of low-loss blade tip.


Author(s):  
Sridhar Murari ◽  
Sathish Sunnam ◽  
Jong S. Liu

With the advent of fast computers and availability of less costly memory resources, computational fluid dynamics (CFD) has emerged as a powerful tool for the design and analysis of flow and heat transfer of high pressure turbine stages. CFD gives an insight in to flow patterns that are difficult, expensive or impossible to study using experimental techniques. However, the application of CFD depends on its accuracy and reliability. This requires the CFD code to be validated with laboratory measurements to ensure its predictive capacity. In the continual effort to improve analysis and design techniques, Honeywell has been investigating in the use of CFD to predict the aerodynamic performance of a high pressure turbine. Reynolds Averaged Navier Stokes (RANS), unsteady models like detached eddy simulation (DES), large eddy simulation (LES), and Scale Adaptive Simulation (SAS) are used to predict the aerodynamic performance of a high pressure turbine. Mixing plane approach is used to address the flow data transport across the stationary interface in RANS simulation. The film holes on blade surface and end walls for all the analysis are modeled by using actual film hole modeling technique. The validation is accomplished with the test results of a high pressure turbine, Energy Efficient Engine (E3). The aerodynamic performance data at design point, typical off-design points are taken as test cases for the validation study. One dimensional performance parameters such as corrected mass flow rate, total pressure ratio, cycle efficiency, and two dimensional spanwise distributions of total pressure, total temperature and flow angle that are obtained from CFD results are compared with test data. Streamlines and flow field results at different measurement planes are presented to understand the aerodynamic behavior.


Sadhana ◽  
2005 ◽  
Vol 30 (5) ◽  
pp. 625-648 ◽  
Author(s):  
Hüseyİn Yapici ◽  
Gamze Baştürk ◽  
Nesrİn KayataŞ ◽  
Şenay Yalçin

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