energies Article Influence of Swirl Clocking on the Performance of Turbine Stage with Three-Dimensional Nozzle Guide Vane Shinyoung Jeon 1, Changmin Son 2,* and Jinuk Kim 3 1 School of Mechanical Engineering, Pusan National University, Pusan 46241, Korea; [email protected] 2 Department of Mechanical Engineering, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, USA 3 Gas Turbine Center, Doosan Heavy Industries & Construction, Changwon 51711, Korea; [email protected] * Correspondence: [email protected]; Tel.: +1-540-231-1924 Abstract: The effect of the swirl clocking on three-dimensional nozzle guide vane (NGV) is investi- gated using computational fluid dynamics. The research reports the loss characteristics of leaned and swept NGVs and the influence of swirl clocking. The three-dimensional NGVs are built by stacking the same 2D profile along different linear axes, characterized by different angles with respect to the normal or radial direction: " = −12◦ ~ +12◦ for the leaned and γ = −5◦ ~ +10◦ for the swept airfoils. A total of 40 models are analyzed to study the effects of lean and sweep on aerodynamic performance. To investigate the influence of swirl clocking, the analysis cases include the center of the swirl that was positioned at the leading edge as well as the middle of the passage. The prediction results show that the relationship of the changes in mass flow rate and throat area are not monotonic. Further observation confirms the redistribution of loading and flow angle under different lean and sweep angles; thus, three-dimensional design is a key influencing factor on aerodynamic performance. In Citation: Jeon, S.; Son, C.; Kim, J. the presence of swirl clocking, NGV performance is changed significantly and the findings offer new Influence of Swirl Clocking on the insight and opportunities to improve three-dimensional NGV airfoil design. Performance of Turbine Stage with Three-Dimensional Nozzle Guide Keywords: total pressure loss; stage efficiency; lean angle; sweep angle Vane. Energies 2021, 14, 5503. https://doi.org/10.3390/en14175503 Academic Editor: Andrea De Pascale 1. Introduction The Nozzle Guide Vane (NGV) of a turbine experiences a highly turbulent combustion Received: 11 August 2021 flow with a complicated swirl structure [1,2]. The role of NGV is to turn the flow to the right Accepted: 31 August 2021 angle for downstream rotor and stages while controlling the flow rate through its throat Published: 3 September 2021 area. In addition, further cooling and structural requirements should be considered to withstand high pressure and temperature operating conditions. Therefore, this motivates Publisher’s Note: MDPI stays neutral researchers to develop robust approaches for improving overall efficiency by controlling with regard to jurisdictional claims in flow through NGV. One of which is to implement lean and sweep angles to the NGV. Lean published maps and institutional affil- is a stacking-line modification in which NGV sections are moved relative to each other in iations. the circumferential direction. For sweep, the modification applies to the axial direction. Therefore, the influence of lean, sweep and swirl on the three-dimensional aerodynamics of turbine passage is of great interest to researchers. The very early concept of radial airfoil stacking was introduced about sixty years ago. Straight lean and compound lean Copyright: © 2021 by the authors. have been recognized as an effective way to control the reaction, loading and secondary Licensee MDPI, Basel, Switzerland. flows [3–11]. It has been reported that the straight lean and compound lean can reorganize This article is an open access article the vortices and reduce the secondary flow loss. As a result, the secondary flow loss distributed under the terms and decreased remarkably by using appropriate leaned blades [12–16]. The sweep commonly conditions of the Creative Commons occurred because the meridional passage of the main annulus is not typically at a constant Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ radius, whereas the NGV is stacked on a near radial line in the meridional views. The 4.0/). secondary flow structure and the pressure distribution of the NGV passage are closely Energies 2021, 14, 5503. https://doi.org/10.3390/en14175503 https://www.mdpi.com/journal/energies Energies 2021, 14, x FOR PEER REVIEW 2 of 26 views. The secondary flow structure and the pressure distribution of the NGV passage are closely linked so that the sweep angle affects the secondary loss mechanism [17,18]. However, the sweep angle may simply shift the loss from the endwall region to mid-span [19,20]. The potential impact and limitation of the understanding were reviewed as the technology developed [21,22]. It has been almost twenty years since the advanced com- putational fluid dynamics (CFD) and experimental approach have been brought into tur- bomachinery research. Comprehensive results from experiments and CFD are reported to enhance the understanding of the root cause [3–7,9–15,17–29]. Furthermore, the design optimization approach is being applied to offer more complicated control of design pa- Energies 2021, 14, 5503 rameters [8,16,30]. 2 of 25 While the previous research on lean and sweep reported its influence on three-di- mensional aerodynamics of airfoil passage, there is rarely any report in conjunction with linked so that the sweep angle affects the secondary loss mechanism [17,18]. However, swirlthe sweep clocking. angle may Similarly, simply shift the the research loss from theon endwall the swirl region effect to mid-span on NGV [19,20 aerodynamic]. perfor- manceThe potential [21,23–26] impact and did limitation not consider of the understanding the lean and were sweep. reviewed The as the present technology study aims to investi- gatedeveloped the influence [21,22]. It has of beenthe almostthree-dimensionali twenty years sincety theof advancedNGV on computational the turbine stage considering fluid dynamics (CFD) and experimental approach have been brought into turbomachinery moreresearch. realistic Comprehensive operation results conditions. from experiments Therefore, and CFD a are1.5 reported stage turbine to enhance with the three-dimensional NGVunderstanding airfoil is of modeled the root cause for [3 simulating–7,9–15,17–29]. the Furthermore, swirl clocking. the design A optimization series of CFD is conducted to (1)approach confirm is being the applied findings to offer from more early complicated research control and of design (2) reveal parameters the [ 8further,16,30]. understanding of While the previous research on lean and sweep reported its influence on three- thedimensional impact aerodynamicsof swirl clocking of airfoil on passage, the stage there pe is rarelyrformance. any report A parametric in conjunction geometry is created forwith the swirl present clocking. study. Similarly, The the parameters research on theto vary swirl effectthe NGV on NGV geometry aerodynamic are the angles of lean (+12performance ~ −12, [21Δ ,23= –6°),26] did compound not consider lean the lean (+12 and ~ sweep. −12, TheΔ = present 6°), and study sweep aims to in-(+10 ~ −5, Δ = 5°). In vestigate the influence of the three-dimensionality of NGV on the turbine stage considering addition,more realistic the operation study conditions.extended Therefore, to include a 1.5 the stage swir turbinel clocking with three-dimensional by positioning the swirl core at theNGV leading airfoil is edge modeled and for simulatingpassage center the swirl of clocking. NGV. A For series the of CFDanalysis, is conducted the variation to of the shape of(1) NGV confirm is the achieved findings from by earlyusing research in-house and (2) tools. reveal Then, the further the understanding produced airfoil of geometries are the impact of swirl clocking on the stage performance. A parametric geometry is created transferredfor the present to study. TurboGrid The parameters (Version to vary 19.2 the R2, NGV ANSYS geometry Inc, are Canonsburg, the angles of lean PA) to generate com- putational(+12 ~ −12, D grids.= 6◦), compound In CFX (Version lean (+12 ~ 19.2−12, DR2,= 6 AN◦), andSYS sweep Inc, (+10 Canonsburg, ~ −5, D = 5◦). InPA), the properties of combustionaddition, the study gas extendedand total to includeto static the swirlpressure clocking ratio by positioning are applied the swirl for corethe atcalculation. Uniform the leading edge and passage center of NGV. For the analysis, the variation of the shape inletof NGV total is achieved temperature by using and in-house adiabatic tools. Then,walls the ar producede assumed. airfoil To geometries model turbulence, are SST (Shear Stresstransferred Transport) to TurboGrid is (Versionselected 19.2 with R2, ANSYS an inlet Inc., freestream Canonsburg, PA,turbulence USA) to generate intensity of 5%. In total, 108computational cases are grids.analyzed In CFX for (Version the present 19.2 R2, ANSYSinvestigation. Inc., Canonsburg, PA, USA), the properties of combustion gas and total to static pressure ratio are applied for the calculation. Uniform inlet total temperature and adiabatic walls are assumed. To model turbulence, 2.SST Computational (Shear Stress Transport) Model is selected and Approach with an inlet freestream turbulence intensity of 5%. In total,A nozzle 108 cases guide are analyzed vane for of the the present first investigation.stage turbine of an industrial gas turbine is used as a baseline2. Computational configuration Model and for Approach CFD validation. The airfoil at 50% span height is shown in Fig- ure 1.A The nozzle NGV guide has vane an of axial the first chord stage of turbine 123.6 of mm an industrial at 50% span gas turbine height is usedand a total of 48 airfoils aroundas a baseline the configurationannulus. The for CFDheight validation. of the The airfoil airfoil is at 157.20 50% span mm height at isthe shown leading edge (LE) and in Figure1. The NGV has an axial chord of 123.6 mm at 50% span height and a total of the48airfoils NGVaround exit angle the annulus.