International Journal of Heat and Fluid Flow, Volume 44, December 2013

The accurate prediction of fluid flow within rotating systems has a primary role for the reliability and performance of rotating machineries. The selection of a suitable model to account for the effects of turbulence on such complex flows remains an open issue in the literature. This paper reports a numerical benchmark of different approaches available within commercial CFD solvers together with results obtained by means of in-house developed or open-source available research codes exploiting a suitable Reynolds Stress Model (RSM) closure, Large Eddy Simulation (LES) and a direct numerical simulation (DNS). The predictions are compared to the experimental data of Burin et al. (2010) in an original enclosed Couette–Taylor apparatus with endcap rings. The results are discussed in details for both the mean and turbulent fields. A particular attention has been turned to the scaling of the turbulent angular momentum G with the Reynolds number Re. By DNS, G is found to be proportional to Re^α, the exponent α = 1.9 being constant in our case for the whole range of Reynolds numbers. Most of the approaches predict quite well the good trends apart from the k–ω SST model, which provides relatively poor agreement with the experiments even for the mean tangential velocity profile. Among the RANS models, even though no approach appears to be fully satisfactory, the RSM closure offers the best overall agreement.

https://www.sciencedirect.com/science/article/pii/S0142727X13001252

https://www.researchgate.net/publication/258935419_Turbulent_Couette-Taylor_flows_with_endwall_effects_A_numerical_benchmark

International Journal of Heat and Fluid Flow, Elsevier, 2013

New calculations using an innovative Reynolds Stress Model are compared to velocity measurements performed by Particle Image Velocimetry technique and the predictions of a k–w SST model in the case of an impinging jet flow onto a rotating disk in a discoidal and unshrouded rotor–stator system. The cavity is characterized by a dimensionless spacing interval G = 0.02 and a low aspect ratio for the jet e/D = 0.25. Jet Reynolds numbers ranging from 1.72e4 to 4.3e4 and rotational Reynolds numbers between 0.33e5 and 5.32e5 are considered. Three flow regions have been identified: a jet-dominated flow area at low radii characterized by a zero tangential velocity, a mixed region at intermediate radii and rotation-dominated flow region outwards. For all parameters, turbulence, which tends to the isotropic limit in the core, is much intense in a region located after the impingement zone. A relative good agreement between the PIV measurements and the predictions of the RSM has been obtained in terms of the radial distributions of the core-swirl ratio and of the turbulence intensities. The k–w SST model over-estimates these flow characteristics in the jet dominated area. For the thermal field, the heat transfers are enhanced in the jet dominated region and decreases towards the periphery of the cavity. The jet Reynolds number appears to have a preponderant effect compared to the rotational one on the heat transfer distribution. The two RANS modelings compare quite well with the heat transfer measurements for these ranges of parameters.

https://www.sciencedirect.com/science/article/pii/S0142727X13001975

https://www.researchgate.net/publication/258935331_Turbulent_impinging_jet_flow_into_an_unshrouded_rotor-stator_system_Hydrodynamics_and_heat_transfer

Proceedings of ASME Turbo Expo 2013 – GT2013-94673

A numerical study of a state of the art leading edge cooling scheme was performed to analyze the heat transfer process within the leading edge cavity of a high pressure turbine airfoil. The investigated geometries account a trapezoidal supply channel with a large racetrack impingement holes. The coolant jets, confined among two consequent large fins, impact the leading edge internal surface and it is extracted from the leading edge cavity through both showerhead holes and film cooling holes. The CFD setup has been validated by means of the experimental measurements performed on a dedicated test rig developed and operated at University of Florence. The aim of this study is to investigate the combined effects of jet impingement, mass flow extraction and fins presence on the internal heat transfer of the leading edge cavity. More in details, the paper analyses the impact, in terms of blade metal temperature, of large fins presence and positioning. Jet’s Reynolds number is varied in order to cover the typical engine conditions of these cooling systems (Re_j = 20000 – 40000).

http://proceedings.asmedigitalcollection.asme.org/proceeding.aspx?articleid=1776087

https://www.researchgate.net/publication/267504204_Numerical_Analysis_of_Heat_Transfer_in_a_Leading_Edge_Geometry_With_Racetrack_Holes_and_Film_Cooling_Extraction

International Journal of Rotating Machinery, Sep 2012

Heat transfer and pressure drop for a representative part of a turbine active cooling system were numerically investigated by means of an in-house code. This code has been developed in the framework of an internal research program and has been validated by experiments and CFD. The analysed system represents the classical open bird cage arrangement that consists of an air supply pipe with a control valve and the present system with a collector box and pipes, which distribute cooling air in circumferential direction of the casing. The cooling air leaves the ACC system through small holes at the bottom of the tubes. These tubes extend at about 180° around the casing and may involve a huge number of impinging holes; as a consequence, the impinging jets mass flow rate may vary considerably along the feeding manifold with a direct impact on the achievable heat transfer levels. This study focuses on the performance, in terms of heat transfer coefficient and pressure drop, of several impinging tube geometries. As a result of this analysis, several design solutions have been compared and discussed.

https://www.hindawi.com/journals/ijrm/2012/103583/

https://www.researchgate.net/publication/260246390_Aerothermal_analysis_of_a_turbine_casing_impingement_cooling_system

Proceedings of ASME Turbo Expo 2012 – GT2012-68592

Reliable means of predicting ingestion in cavities adjacent to the main gas path are increasingly being sought by engineers involved in the design of gas turbines. In this paper, analysis is to be presented that results from an extended research programme, MAGPI, sponsored by the EU and several leading gas turbine manufactures and universities. Extensive use is made of CFD modelling techniques to understand the aerodynamic behaviour of a turbine stator well cavity, focusing on the interaction of cooling air supply with the main annulus gas. The objective of the study has been to benchmark a number of CFD codes and numerical techniques covering RANS and URANS calculations with different turbulence models in order to assess the suitability of the standard settings used in the industry for calculating the mechanics of the flow travelling between cavities in a turbine through the main gas path.

The modelling methods employed have been compared making use of experimental data gathered from a dedicated two-stage turbine rig, running at engine representative conditions. Extensive measurements are available for a range of flow conditions and alternative cooling arrangements. The limitations of the numerical methods in calculating the interaction of the cooling flow egress and the main stream gas, and subsequent ingestion into downstream cavities in the engine (i.e. re-ingestion), have been exposed. This has been done without losing sight of the validation of the CFD for its use for predicting heat transfer, which was the main objective of the partners of the MAGPI Work-Package 1 consortium.

http://proceedings.asmedigitalcollection.asme.org/proceeding.aspx?articleid=1694463

https://www.researchgate.net/publication/267503304_An_Investigation_Into_Numerical_Analysis_Alternatives_for_Predicting_Re-Ingestion_in_Turbine_Disc_Rim_Cavities

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Heat transfer and discharge coefficient behaviour for a representative part of a turbine active cooling system were numerically investigated by means of an in-house code. This code has been developed in the framework of an internal research program and has been validated by experiments and CFD. The analysed system represents the classical open bird cage arrangement that consists of an air supply pipe with a control valve and the present system with a collector box and pipes, which distribute cooling air in circumferential direction of the casing. The cooling air leaves the ACC system through small holes at the bottom of the tubes. These tubes extend at about 180° around the casing and may involve a huge number of impinging holes; as a consequence, the impinging jets mass flow rate may vary considerably along the feeding manifold with a direct impact on the achievable heat transfer levels. This study focuses on the performance, in terms of heat transfer coefficient and pressure drop, of several impinging tube geometries. As a result of this analysis, several design solutions have been compared and discussed.

http://proceedings.asmedigitalcollection.asme.org/proceeding.aspx?articleid=1694498

https://www.researchgate.net/publication/267503620_Heat_Transfer_and_Pressure_Drop_Analysis_of_a_Turbine_Casing_Impingement_Cooling_System

Journal of Turbomachinery 135(3), May 2013

Transaction of ASME Turbo Expo 2012 – GT2012-69581

An experimental survey on a state of the art leading edge cooling scheme was performed to evaluate heat transfer coefficients (HTC) on a large scale test facility simulating a high pressure turbine airfoil leading edge cavity. The test section includes a trapezoidal supply channel with three large racetrack impingement holes. On the internal surface of the leading edge, four big fins are placed in order to confine impingement jets. The coolant flow impacts the leading edge internal surface, and it is extracted from the leading edge cavity through 24 showerhead holes and 24 film cooling holes. The aim of the present study is to investigate the combined effects of jet impingement and mass flow extraction on the internal heat transfer of the leading edge. A nonuniform mass flow extraction was also imposed to reproduce the effects of the pressure side and suction side external pressure. Measurements were performed by means of a transient technique using narrow band thermochromic liquid crystals (TLCs). Jet Reynolds number and crossflow conditions into the supply channel were varied in order to cover the typical engine conditions of these cooling systems (Rej=10,000−40,000Rej=10,000-40,000). Experiments were compared with a numerical analysis on the same test case in order to better understand flow interaction inside the cavity. Results are reported in terms of detailed 2D maps, radial-wise, and span-wise averaged values of Nusselt number.

http://turbomachinery.asmedigitalcollection.asme.org/article.aspx?articleid=1672756

https://www.researchgate.net/publication/326263417_Heat_Transfer_Measurements_in_a_Leading_Edge_Cooling_Geometry_under_Rotating_Conditions