Turbulence Modeling and Computation of Viscous Transitional Flows for Low Pressure Turbines

1999 ◽  
Vol 121 (4) ◽  
pp. 824-833 ◽  
Author(s):  
A. Chernobrovkin ◽  
B. Lakshminarayana
Keyword(s):  
Numerical Simulation ◽  
Reynolds Number ◽  
Turbulence Modeling ◽  
Turbulence Models ◽  
Separated Flow ◽  
Low Pressure ◽  
Reynolds Stress Model ◽  
Suction Surface ◽  
Transitional Flows ◽  
Wide Range

Variation of the flow Reynolds number between the take off and cruise conditions significantly affects the boundary layer development on low-pressure turbine blading. A decreased Reynolds number leads to the flow separation on the suction surface of the blading and increased losses. A numerical simulation has been carried out to assess the ability of a Navier-Stokes solver to predict transitional flows in a wide range of Reynolds numbers and inlet turbulence intensities. A number of turbulence models (including the Algebraic Reynolds Stress Model) and transition models have been employed to analyze the reliability and accuracy of the numerical simulation. A comparison between the prediction and the experimental data reveals good correlation. However, the analysis shows that the artificial dissipation in the numerical solver may have a profound effect on the prediction of the transition in a separated flow.

Direct Numerical Simulation of Turbulent Flow and Aeroacoustic Fields Around an Airfoil Using Lattice Boltzmann Method

2016 ◽  
Author(s):  
Kazuya Kusano ◽  
Kazutoyo Yamada ◽  
Masato Furukawa ◽  
Kil-Ju Moon
Keyword(s):  
Numerical Simulation ◽  
Boundary Layer ◽  
Reynolds Number ◽  
Direct Numerical Simulation ◽  
Lattice Boltzmann Method ◽  
Lattice Boltzmann ◽  
Separated Flow ◽  
Broadband Noise ◽  
Suction Surface ◽  
Boltzmann Method

The paper presents a result of the direct numerical simulation with the lattice Boltzmann method which was conducted for quantitative prediction of turbulent broadband noise. For better prediction of broadband noise with high frequency, which is generally generated in high Reynolds number flows, not only high grid resolution is required for a flow simulation to capture very small eddies of the sound source inside the turbulent boundary layer, but also the computation of acoustic field is often needed. In such case, the direct simulation of flow field and acoustic field is straightforward and effective. In this study, the direct simulation with the lattice Boltzmann method was conducted for a flow around the NACA0012 airfoil with the Reynolds number of two hundred thousand. In order to efficiently simulate this high Reynolds number flow with the LBM, the multi-scale approach was introduced in conjunction with the Building-cube method, while keeping the advantage of the LBM with the Cartesian mesh. At the condition with angle-of-attack of 9 degrees, a laminar separation bubble arises on the suction surface near the leading-edge and the suction boundary layer downstream of it is turbulent due to the separated-flow transition. As a result, turbulent broadband noise is generated from the boundary layer over the airfoil with the separated-flow transition. In the paper, as for prediction of such broadband noise, the computed frequency spectrum of far-field sound is validated to agree with the experimental result. In addition, through the detailed analyses of turbulent properties of the turbulent boundary layer on the suction surface, the validity of the present direct numerical simulation is demonstrated.

Designing Low-Pressure Turbine Blades With Integrated Flow Control

2005 ◽  
Author(s):  
Jeffrey P. Bons ◽  
Laura C. Hansen ◽  
John P. Clark ◽  
Peter J. Koch ◽  
Rolf Sondergaard
Keyword(s):  
Reynolds Number ◽  
Flow Control ◽  
Turbine Blade ◽  
Separation Bubble ◽  
Low Pressure ◽  
Suction Surface ◽  
Flow Measurements ◽  
Blade Loading ◽  
Low Pressure Turbine ◽  
Wide Range

A low pressure turbine blade was designed to produce a 17% increase in blade loading over an industry-standard airfoil using integrated flow control to prevent separation. The design was accomplished using two-dimensional CFD predictions of blade performance coupled with insight gleaned from recently published work in transition modeling and from previous experiments with flow control using vortex generator jets (VGJs). In order to mitigate the Reynolds number lapse in efficiency associated with LPT airfoils, a mid-loaded blade was selected. Also, separation predictions from the computations were used to guide the placement of control actuators on the blade suction surface. Three blades were fabricated using the new design and installed in a two-passage linear cascade facility. Flow velocity and surface pressure measurements taken without activating the VGJs indicate a large separation bubble centered at 68% axial chord on the suction surface. The size of the separation and its growth with decreasing Reynolds number agree well with CFD predictions. The separation bubble reattaches to the blade over a wide range of inlet Reynolds numbers from 150,000 down to below 20,000. This represents a marked improvement in separation resistance compared to the original blade profile which separates without reattachment below a Reynolds number of 40,000. This enhanced performance is achieved by increasing the blade spacing while simultaneously adjusting the blade shape to make it less aft-loaded but with a higher peak cp. This reduces the severity of the adverse pressure gradient in the uncovered portion of the modified blade passage. With the use of pulsed VGJs, the design blade loading was achieved while providing attached flow over the entire range of Re. Detailed phase-locked flow measurements using three-component PIV show the trajectory of the jet and its interaction with the unsteady separation bubble. Results illustrate the importance of integrating flow control into the turbine blade design process and the potential for enhanced turbine performance.

scholarly journals The Turbulent Flow over the BARC Rectangular Cylinder: A DNS Study

2021 ◽  
Author(s):  
Alessandro Chiarini ◽  
Maurizio Quadrio
Keyword(s):  
Numerical Simulation ◽  
Reynolds Number ◽  
Direct Numerical Simulation ◽  
Finite Differences ◽  
Turbulence Models ◽  
Fine Tuning ◽  
Rectangular Cylinder ◽  
Budget Equation ◽  
Complete Set ◽  
First Time

AbstractA direct numerical simulation (DNS) of the incompressible flow around a rectangular cylinder with chord-to-thickness ratio 5:1 (also known as the BARC benchmark) is presented. The work replicates the first DNS of this kind recently presented by Cimarelli et al. (J Wind Eng Ind Aerodyn 174:39–495, 2018), and intends to contribute to a solid numerical benchmark, albeit at a relatively low value of the Reynolds number. The study differentiates from previous work by using an in-house finite-differences solver instead of the finite-volumes toolbox OpenFOAM, and by employing finer spatial discretization and longer temporal average. The main features of the flow are described, and quantitative differences with the existing results are highlighted. The complete set of terms appearing in the budget equation for the components of the Reynolds stress tensor is provided for the first time. The different regions of the flow where production, redistribution and dissipation of each component take place are identified, and the anisotropic and inhomogeneous nature of the flow is discussed. Such information is valuable for the verification and fine-tuning of turbulence models in this complex separating and reattaching flow.

The Effect of Pulsed Blowing on the Boundary Layer of a Highly Loaded Low Pressure Turbine Blade

2013 ◽  
Author(s):  
Marion Mack ◽  
Roland Brachmanski ◽  
Reinhard Niehuis
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Mach Number ◽  
Suction Side ◽  
Reynolds Numbers ◽  
Low Pressure ◽  
Trailing Edge ◽  
Low Pressure Turbine ◽  
Wide Range ◽  
Highly Loaded

The performance of the low pressure turbine (LPT) can vary appreciably, because this component operates under a wide range of Reynolds numbers. At higher Reynolds numbers, mid and aft loaded profiles have the advantage that transition of suction side boundary layer happens further downstream than at front loaded profiles, resulting in lower profile loss. At lower Reynolds numbers, aft loading of the blade can mean that if a suction side separation exists, it may remain open up to the trailing edge. This is especially the case when blade lift is increased via increased pitch to chord ratio. There is a trend in research towards exploring the effect of coupling boundary layer control with highly loaded turbine blades, in order to maximize performance over the full relevant Reynolds number range. In an earlier work, pulsed blowing with fluidic oscillators was shown to be effective in reducing the extent of the separated flow region and to significantly decrease the profile losses caused by separation over a wide range of Reynolds numbers. These experiments were carried out in the High-Speed Cascade Wind Tunnel of the German Federal Armed Forces University Munich, Germany, which allows to capture the effects of pulsed blowing at engine relevant conditions. The assumed control mechanism was the triggering of boundary layer transition by excitation of the Tollmien-Schlichting waves. The current work aims to gain further insight into the effects of pulsed blowing. It investigates the effect of a highly efficient configuration of pulsed blowing at a frequency of 9.5 kHz on the boundary layer at a Reynolds number of 70000 and exit Mach number of 0.6. The boundary layer profiles were measured at five positions between peak Mach number and the trailing edge with hot wire anemometry and pneumatic probes. Experiments were conducted with and without actuation under steady as well as periodically unsteady inflow conditions. The results show the development of the boundary layer and its interaction with incoming wakes. It is shown that pulsed blowing accelerates transition over the separation bubble and drastically reduces the boundary layer thickness.

Redesign of High-Lift LP-Turbine Airfoils for Low Speed Testing

2010 ◽  
Author(s):  
Michele Marconcini ◽  
Filippo Rubechini ◽  
Roberto Pacciani ◽  
Andrea Arnone ◽  
Francesco Bertini
Keyword(s):  
Separated Flow ◽  
Low Pressure ◽  
High Lift ◽  
Low Speed ◽  
Low Pressure Turbine ◽  
Wide Range ◽  
Flow Configurations ◽  
Artificial Neural Network Ann ◽  
Lp Turbine ◽  
Turbine Airfoils

Low pressure turbine airfoils of the present generation usually operate at subsonic conditions, with exit Mach numbers of about 0.6. To reduce the costs of experimental programs it can be convenient to carry out measurements in low speed tunnels in order to determine the cascades performance. Generally speaking, low speed tests are usually carried out on airfoils with modified shape, in order to compensate for the effects of compressibility. A scaling procedure for high-lift, low pressure turbine airfoils to be studied in low speed conditions is presented and discussed. The proposed procedure is based on the matching of a prescribed blade load distribution between the low speed airfoil and the actual one. Such a requirement is fulfilled via an Artificial Neural Network (ANN) methodology and a detailed parameterization of the airfoil. A RANS solver is used to guide the redesign process. The comparison between high and low speed profiles is carried out, over a wide range of Reynolds numbers, by using a novel three-equation, transition-sensitive, turbulence model. Such a model is based on the coupling of an additional transport equation for the so-called laminar kinetic energy (LKE) with the Wilcox k–ω model and it has proven to be effective for transitional, separated-flow configurations of high-lift cascade flows.

An Experimental Investigation of the Effect of Freestream Turbulence on the Wake of a Separated Low-Pressure Turbine Blade at Low Reynolds Numbers

1999 ◽  
Vol 122 (2) ◽  
pp. 431-433 ◽  
Author(s):  
C. G. Murawski ◽  
K. Vafai
Keyword(s):  
Reynolds Number ◽  
Turbine Blade ◽  
Turbulence Intensity ◽  
Reynolds Numbers ◽  
Low Pressure ◽  
Freestream Turbulence ◽  
Suction Surface ◽  
Low Reynolds Numbers ◽  
Low Pressure Turbine ◽  
Flow Reynolds Number

An experimental study was conducted in a two-dimensional linear cascade, focusing on the suction surface of a low pressure turbine blade. Flow Reynolds numbers, based on exit velocity and suction length, have been varied from 50,000 to 300,000. The freestream turbulence intensity was varied from 1.1 to 8.1 percent. Separation was observed at all test Reynolds numbers. Increasing the flow Reynolds number, without changing freestream turbulence, resulted in a rearward movement of the onset of separation and shrinkage of the separation zone. Increasing the freestream turbulence intensity, without changing Reynolds number, resulted in shrinkage of the separation region on the suction surface. The influences on the blade’s wake from altering freestream turbulence and Reynolds number are also documented. It is shown that width of the wake and velocity defect rise with a decrease in either turbulence level or chord Reynolds number. [S0098-2202(00)00202-9]

Transition Mechanisms in Laminar Separated Flow Under Simulated Low Pressure Turbine Aerofoil Conditions

2012 ◽  
Vol 135 (1) ◽  
Author(s):  
Jerrit Dähnert ◽  
Christoph Lyko ◽  
Dieter Peitsch
Keyword(s):  
Reynolds Number ◽  
Separation Bubble ◽  
Separated Flow ◽  
Low Pressure ◽  
Main Flow ◽  
Test Facility ◽  
Flow Conditions ◽  
Laminar Separation ◽  
Free Stream Turbulence ◽  
Low Pressure Turbine

Based on detailed experimental work conducted at a low speed test facility, this paper describes the transition process in the presence of a separation bubble with low Reynolds number, low free-stream turbulence, and steady main flow conditions. A pressure distribution has been created on a long flat plate by means of a contoured wall opposite of the plate, matching the suction side of a modern low-pressure turbine aerofoil. The main flow conditions for four Reynolds numbers, based on suction surface length and nominal exit velocity, were varied from 80,000 to 300,000, which covers the typical range of flight conditions. Velocity profiles and the overall flow field were acquired in the boundary layer at several streamwise locations using hot-wire anemometry. The data given is in the form of contours for velocity, turbulence intensity, and turbulent intermittency. The results highlight the effects of Reynolds number, the mechanisms of separation, transition, and reattachment, which feature laminar separation-long bubble and laminar separation-short bubble modes. For each Reynolds number, the onset of transition, the transition length, and the general characteristics of separated flow are determined. These findings are compared to the measurement results found in the literature. Furthermore, the experimental data is compared with two categories of correlation functions also given in the literature: (1) correlations predicting the onset of transition and (2) correlations predicting the mode of separated flow transition. Moreover, it is shown that the type of instability involved corresponds to the inviscid Kelvin-Helmholtz instability mode at a dominant frequency that is in agreement with the typical ranges occurring in published studies of separated and free-shear layers.

The Effect of Reynolds Number and Velocity Distribution on LP Turbine Cascade Performance

1986 ◽  
Author(s):  
D. J. Patterson ◽  
M. Hoeger
Keyword(s):  
Reynolds Number ◽  
Pressure Distribution ◽  
Guide Vane ◽  
Flow Visualisation ◽  
Suction Surface ◽  
Trailing Edge ◽  
Wide Range ◽  
Oil Flow ◽  
Low Reynolds ◽  
Lp Turbine

Because of the laminar boundary-layer’s inability to withstand moderate adverse pressure gradients without separating, profile losses in LP turbines operating at low Reynolds numbers can be high. The choice of design pressure distribution for the blading is thus of great importance. Three sub-sonic LP turbine nozzle-guide-vane cascade profiles have been tested over a wide range of incidence, Mach number and Reynolds number. The three profiles are of low, medium and high deflection and, as such, display significantly different pressure distributions. The tests include detailed boundary-layer traverses, trailing-edge base-pressure monitoring and oil-flow visualisation. It is shown that the loss variation with Reynolds number is a function of pressure distribution and that the trailing-edge loss component is dominant at low Reynolds number. The importance of achieving late flow transition — rather than separation — in the suction-surface trailing-edge region is stressed. The paper concludes by remarking on the advantages and practical implications of each loading design.

scholarly journals The Problem of Airflow Around Building Clusters in Different Configurations

2017 ◽  
Vol 64 (3) ◽  
pp. 401-418 ◽  
Author(s):  
Mateusz Jędrzejewski ◽  
Marta Poćwierz ◽  
Katarzyna Zielonko-Jung
Keyword(s):  
Numerical Simulation ◽  
Wind Tunnel ◽  
Pressure Measurement ◽  
Turbulence Models ◽  
Reynolds Stress Model ◽  
Complex Model ◽  
Stress Model ◽  
Qualitative Information ◽  
Pressure Coefficients ◽  
Rsm Model

Abstract In the paper, the authors discuss the construction of a model of an exemplary urban layout. Numerical simulation has been performed by means of a commercial software Fluent using two different turbulence models: the popular k-ε realizable one, and the Reynolds Stress Model (RSM), which is still being developed. The former is a 2-equations model, while the latter – is a RSM model – that consists of 7 equations. The studies have shown that, in this specific case, a more complex model of turbulence is not necessary. The results obtained with this model are not more accurate than the ones obtained using the RKE model. The model, scale 1:400, was tested in a wind tunnel. The pressure measurement near buildings, oil visualization and scour technique were undertaken and described accordingly. Measurements gave the quantitative and qualitative information describing the nature of the flow. Finally, the data were compared with the results of the experiments performed. The pressure coefficients resulting from the experiment were compared with the coefficients obtained from the numerical simulation. At the same time velocity maps and streamlines obtained from the calculations were combined with the results of the oil visualisation and scour technique.

A Critical Evaluation of Turbulence Modeling in a Model Combustor

2012 ◽  
Author(s):  
Leiyong Jiang
Keyword(s):  
Turbulence Modeling ◽  
Critical Evaluation ◽  
Turbulence Models ◽  
Reynolds Stress Model ◽  
Operating Conditions ◽  
Moment Closure ◽  
Mean Velocity ◽  
Second Moment Closure ◽  
Heat Transfers ◽  
Air Diffusion

Based on the previous benchmark studies on combustion, scalar transfer and radiation models, a critical evaluation of turbulence models in a propane-air diffusion flame combustor with interior and exterior conjugate heat transfers has been performed. Results obtained from six turbulence models are presented and compared in detail with a comprehensive database obtained from a series of experimental measurements. It is found that the Reynolds stress model (RSM), a second moment closure, is superior over the five popular eddy-viscosity two-equation models. Although the main flow patterns are captured by all six turbulence models, only the RSM is able to successfully predict the lengths of both recirculation zones and give fairly accurate predictions for mean velocity, temperature, CO2 and CO mole fractions, as well as turbulence kinetic energy in the combustor chamber. In addition, the realizable k-ε (Rk-ε) model illustrates better performance than four other two-equation models and can provide comparable results to those from the RSM for the configuration and operating conditions considered in the present study.

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