Bulletin of the American Physical Society
68th Annual Meeting of the APS Division of Fluid Dynamics
Volume 60, Number 21
Sunday–Tuesday, November 22–24, 2015; Boston, Massachusetts
Session E8: CFD: Turbomachinery |
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Chair: Reza Sheikhi, Northeastern University Room: 108 |
Sunday, November 22, 2015 4:50PM - 5:03PM |
E8.00001: Computational study of a High Pressure Turbine Nozzle/Blade Interaction James Kopriva, Gregory Laskowski, Reza Sheikhi A downstream high pressure turbine blade has been designed for this study to be coupled with the upstream uncooled nozzle of Arts and Rouvroit [1992]. The computational domain is first held to a pitch-line section that includes no centrifugal forces (linear sliding-mesh). The stage geometry is intended to study the fundamental nozzle/blade interaction in a computationally cost efficient manner. Blade/Nozzle count of 2:1 is designed to maintain computational periodic boundary conditions for the coupled problem. Next the geometry is extended to a fully 3D domain with endwalls to understand the impact of secondary flow structures. A set of systematic computational studies are presented to understand the impact of turbulence on the nozzle and down-stream blade boundary layer development, resulting heat transfer, and downstream wake mixing in the absence of cooling. Doing so will provide a much better understanding of stage mixing losses and wall heat transfer which, in turn, can allow for improved engine performance. Computational studies are performed using WALE (Wale Adapted Local Eddy), IDDES (Improved Delayed Detached Eddy Simulation), SST (Shear Stress Transport) models in Fluent. [Preview Abstract] |
Sunday, November 22, 2015 5:03PM - 5:16PM |
E8.00002: Impact of tip-gap size and periodicity on turbulent transition Alexej Pogorelov, Matthias Meinke, Wolfgang Schroeder Large-Eddy Simulations of the flow field in an axial fan are performed at a Reynolds number of 936.000 based on the diameter and the rotational speed of the casing wall. A finite-volume flow solver based on a conservative Cartesian cut-cell method is used to solve the unsteady compressible Navier-Stokes equations. Computations are performed at a flow rate coefficient of 0.165 and a tip-gap size of s/D$=$0.01, for a 72 degrees fan section resolving only one out of five blades and a full fan resolving all five blades to investigate the impact of the periodic boundary condition. Furthermore, a grid convergence study is performed using four computational grids. Results of the flow field are analyzed for the computational grid with 1 billion cells. An interaction of the turbulent wake, generated by the tip-gap vortex, with the downstream blade, is observed, which leads to a cyclic transition with high pressure fluctuations on the suction side of the blade. Two dominant frequencies are identified which perfectly match with the characteristic frequencies in the experimental sound power level such that their physical origin is explained. A variation of the tip-gap size alters the transition on the suction side, i.e., no cyclic transition is observed. [Preview Abstract] |
Sunday, November 22, 2015 5:16PM - 5:29PM |
E8.00003: Application of dynamic slip wall modeling to a turbine nozzle guide vane Sanjeeb Bose, Chaitanya Talnikar, Patrick Blonigan, Qiqi Wang Resolution of near-wall turbulent structures is computational prohibitive necessitating the need for wall-modeled large-eddy simulation approaches. Standard wall models are often based on assumptions of equilibrium boundary layers, which do not necessarily account for the dissimilarity of the momentum and thermal boundary layers. We investigate the use of the dynamic slip wall boundary condition (Bose and Moin, 2014) for the prediction of surface heat transfer on a turbine nozzle guide vane (Arts and de Rouvroit, 1992). The heat transfer coefficient is well predicted by the slip wall model, including capturing the transition to turbulence. The sensitivity of the heat transfer coefficient to the incident turbulence intensity will additionally be discussed. Lastly, the behavior of the thermal and momentum slip lengths will be contrasted between regions where the strong Reynolds analogy is invalid (near transition on the suction side) and an isothermal, zero pressure gradient flat plate boundary layer (Wu and Moin, 2010). [Preview Abstract] |
Sunday, November 22, 2015 5:29PM - 5:42PM |
E8.00004: Turbulence Model Evaluation on a High Pressure Turbine Stage 1 Vane Michal Osusky, Sara Rostami, Aamir Shabbir The accuracy of turbulence modeling depends heavily on the choice of turbulence model. Many turbulence models are only valid for a narrow range of flow regimes, and can produce numerically converged, but physically inaccurate results when applied outside the scope of their intended use. Additionally, the underlying modeling assumptions, such as the linear Boussinesq approximation, impacts the evolution of turbulence in the flow field. As part of the current work, we will study the impact of using various commonly used RANS turbulence models, such as k-omega, BSL, and SST, with and without transition modeling, on the flow field of realistic engine geometries. Additionally, advanced, non-linear turbulence models, such as the Explicit Algebraic Reynolds Stress Model (EARSM), will also be studied for their potential benefits in capturing additional physics in the simulation. Preliminary results show that the EARSM model has a significant impact on the location on laminar to turbulent transition, versus the SST model. All computational results will be compared against detailed experimental data. [Preview Abstract] |
Sunday, November 22, 2015 5:42PM - 5:55PM |
E8.00005: Compressible DNS of transitional and turbulent flow in a low pressure turbine cascade Rajesh Ranjan, Suresh Deshpande, Roddam Narasimha Direct numerical simulation (DNS) of flow in a low pressure turbine cascade at high incidence is performed using a new in-house code ANUROOP. This code solves compressible Navier-Stokes equations in conservative form using finite volume technique and uses kinetic-energy consistent scheme for the flux calculations. ANUROOP is capable of handling flow past complex geometries using hybrid grid approach (separate grid topologies for the boundary layer and rest of the blade passage). This approach offers much more control in mesh spacing and distribution compared to elliptic grid technique, which is used in many previous studies. Also, in contrast to previous studies, focus of the current work is mainly on the boundary layer flow. The flow remains laminar on the pressure side of the blade, but separates in the aft region of the suction side leading to transition. Separation bubbles formed at this region are transient in nature and we notice multiple bubbles merging and breaking in time. In the mean flow however, only one bubble is seen. Velocity profiles very near to the leading edge of the suction side suggest strong curvature effect. Higher-order boundary layer theory that includes effect of curvature is found to be necessary to characterize the flow in this region. Also, the grid convergence study reveals interesting aspects of numerics vital for accurate simulation of this kind of complex flows. [Preview Abstract] |
Sunday, November 22, 2015 5:55PM - 6:08PM |
E8.00006: Unsteady adjoint of a gas turbine inlet guide vane Chaitanya Talnikar, Qiqi Wang Unsteady fluid flow simulations like large eddy simulation have been shown to be crucial in accurately predicting heat transfer in turbomachinery applications like transonic flow over an inlet guide vane. To compute sensitivities of aerothermal objectives for a vane with respect to design parameters an unsteady adjoint is required. In this talk we present unsteady adjoint solutions for a vane from VKI using pressure loss and heat transfer over the vane surface as the objectives. The boundary layer on the suction side near the trailing edge of the vane is turbulent and this poses a challenge for an adjoint solver. The chaotic dynamics cause the adjoint solution to diverge exponentially to infinity from that region when simulated backwards in time. The prospect of adding artificial viscosity to the adjoint equations to dampen the adjoint fields is investigated. Results for the vane from simulations performed on the Titan supercomputer will be shown and the effect of the additional viscosity on the accuracy of the sensitivities will be discussed. [Preview Abstract] |
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