Influences of Inlet Swirl Distributions on an Inter-Turbine Duct: Part I—Casing Swirl Variation

2011 ◽  
Author(s):  
Shuzhen Hu ◽  
Yanfeng Zhang ◽  
Xue Feng Zhang ◽  
Edward Vlasic
Keyword(s):  
Boundary Layer ◽  
Pressure Gradient ◽  
Flow Behavior ◽  
Radial Pressure ◽  
Boundary Layer Separation ◽  
Wake Flow ◽  
Layer Separation ◽  
Swirl Angle ◽  
Inlet Swirl ◽  
Radial Pressure Gradient

The inter-turbine transition duct (ITD) of a gas turbine engine has significant potential for engine weight reduction and/or aerodynamic performance improvement. This potential arises because very little is understood of the flow behavior in the duct in relation to the hub and casing shapes and the flow entering the duct (e.g., swirl angle, turbulence intensity, periodic unsteadiness and blade tip vortices from upstream HP turbine blade rows). In this study, the flow development in an ITD with different inlet swirl distributions was investigated experimentally and numerically. The current paper, which is the first part of a two-part paper, presents the investigations of the influences of the casing swirl variations on the flow physics in the ITD. The results show a fair agreement between the predicted and experimental data. The radial pressure gradient at the first bend of ITD drives the low momentum hub boundary layer and wake flow radially, which results in a pair of hub counter-rotating vortices. Furthermore, the radially moving low momentum wake flow feeds into the casing region and causes 3D casing boundary layer. At the second bend, the reversed radial pressure gradient together with the 3D casing boundary layer generates a pair of casing counter-rotating vortices. Due to the local adverse pressure gradient, 3D boundary layer separation occurs on both the casing and hub at the second bend and the exit of the ITD, respectively. The casing 3D separation enhances the 3D features of the casing boundary layer as well as the existing casing counter-rotating vortices. With increasing casing swirl angle, the casing 3D boundary layer separation is delayed and the casing counter-rotating vortices are weakened. On the other hand, although the hub swirls are kept constant, the hub counter-rotating vortices get stronger with the increasing inlet swirl gradient. The total pressure coefficients within the ITD are significantly redistributed by the casing and hub counter-rotating vortices.

Effects of Area Ratio and Mean Rise Angle on the Aerodynamics of Interturbine Ducts

2018 ◽  
Vol 140 (9) ◽  
Author(s):  
Yanfeng Zhang ◽  
Shuzhen Hu ◽  
Ali Mahallati ◽  
Xue-Feng Zhang ◽  
Edward Vlasic
Keyword(s):  
Boundary Layer ◽  
Pressure Gradient ◽  
Static Pressure ◽  
Computational Study ◽  
Pressure Rise ◽  
Adverse Pressure Gradient ◽  
Boundary Layer Separation ◽  
Wake Flow ◽  
Height Ratio ◽  
Inlet Swirl

This work, a continuation of a series of investigations on the aerodynamics of aggressive interturbine ducts (ITD), is aimed at providing detailed understanding of the flow physics and loss mechanisms in four different ITD geometries. A systematic experimental and computational study was carried out by varying duct outlet-to-inlet area ratios (ARs) and mean rise angles while keeping the duct length-to-inlet height ratio, Reynolds number, and inlet swirl constant in all four geometries. The flow structures within the ITDs were found to be dominated by the boundary layer separation and counter-rotating vortices in both the casing and hub regions. The duct mean rise angle determined the severity of adverse pressure gradient in the casing's first bend, whereas the duct AR mainly governed the second bend's static pressure rise. The combination of upstream wake flow and the first bend's adverse pressure gradient caused the boundary layer to separate and intensify the strength of counter-rotating vortices. At high mean rise angle, the separation became stronger at the casing's first bend and moved farther upstream. At high ARs, a two-dimensional separation appeared on the casing and resulted in increased loss. Pressure loss penalties increased significantly with increasing duct mean rise angle and AR.

Effects of Area Ratio and Mean Rise Angle on the Aerodynamics of Inter-Turbine Ducts

2014 ◽  
Author(s):  
Yanfeng Zhang ◽  
Shuzhen Hu ◽  
Ali Mahallati ◽  
Xue-Feng Zhang ◽  
Edward Vlasic
Keyword(s):  
Boundary Layer ◽  
Pressure Gradient ◽  
Computational Study ◽  
Pressure Rise ◽  
Adverse Pressure Gradient ◽  
Boundary Layer Separation ◽  
Area Ratio ◽  
Wake Flow ◽  
High Area ◽  
Inlet Swirl

The present work, a continuation of a series of investigations on the aerodynamics of aggressive inter-turbine ducts (ITD), is aimed at providing detailed understanding of the flow physics and loss mechanisms in four different ITD geometries. A systematic experimental and computational study was carried out for varying duct mean rise angles and outlet-to-inlet area ratio while keeping the duct length-to-inlet height ratio, Reynolds number and inlet swirl constant in all four geometries. The flow structures within the ITDs were found to be dominated by the counter-rotating vortices and boundary layer separation in both the casing and hub regions. The duct mean rise angle determined the severity of adverse pressure gradient in the casing’s first bend whereas the duct area ratio mainly governed the second bend’s static pressure rise. The combination of upstream wake flow and the first bend’s adverse pressure gradient caused the boundary layer to separate and intensify the strength of counter-rotating vortices. At high mean rise angle, the separation became stronger at the casing’s first bend and moved farther upstream. At high area ratios, a 2-D separation appeared on the casing. Pressure loss penalties increased significantly with increasing duct mean rise angle and area ratio.

Influences of Inlet Swirl Distributions on an Inter-Turbine Duct: Part II—Hub Swirl Variation

2011 ◽  
Author(s):  
Yanfeng Zhang ◽  
Shuzhen Hu ◽  
Xue Feng Zhang ◽  
Edward Vlasic
Keyword(s):  
Boundary Layer ◽  
Total Pressure ◽  
Flow Behavior ◽  
Pressure Coefficient ◽  
Adverse Pressure Gradient ◽  
Wake Flow ◽  
Loss Mechanism ◽  
Turbine Engine ◽  
Swirl Angle ◽  
Inlet Swirl

The inter-turbine transition duct (ITD) of a gas turbine engine has significant potential for engine weight reduction and/or aerodynamic performance improvement. This potential arises because very little is understood of the flow behavior in the duct in relation to the hub and casing shapes and the flow entering the duct (e.g., swirl angle, turbulence intensity, periodic unsteadiness and blade tip vortices from upstream HP turbine blade rows). In this study, the flow development in an ITD with different inlet swirl distributions was investigated experimentally and numerically. The current paper, which is the second part of a two-part paper, presents the investigations of the influences of the hub swirl variations on the flow physics of ITD. The results show that the radial movement of the low momentum hub boundary layer and wake flow induces a pair of hub counter-rotating vortices. This pair of counter-rotating vortices merges with the upstream vorticity, forming a pair of stronger vortices, which persist until ITD exit. Due to the hub streamwise adverse pressure gradient, the hub 3D separation occurs at the exit of the ITD. The hub counter-rotating vortices are strongest with the highest inlet swirl gradient. The hub boundary layer thickness is thickest with the largest inlet hub swirl angle. The hub 3D separation is reduced by the increased hub swirl angle. Based on the studies in both parts of this paper, a detailed loss mechanism has been described. The total pressure coefficient shows that the loss increases gradually at the first bend, and then increases more rapidly at the second bend. The total pressure coefficients within the ITD are significantly redistributed by the casing and hub counter-rotating vortices.

Similarities Between Two-Dimensional and Axisymmetric Vortex Wakes

1977 ◽  
Vol 28 (1) ◽  
pp. 15-20 ◽  
Author(s):  
J E L Simmons
Keyword(s):  
Boundary Layer ◽  
Boundary Layer Separation ◽  
Wake Flow ◽  
Bluff Bodies ◽  
Two Dimensional ◽  
Length Scales ◽  
Layer Separation ◽  
Axisymmetric Vortex ◽  
Axisymmetric Bodies ◽  
Good Agreement

SummaryThis paper presents results of an investigation of the wake flow of a series of two-dimensional bluff bodies with different boundary-layer separation angles. These results are compared with the results of an earlier investigation of a similar series of axisymmetric bodies. It is found that when the same length scales characterising the wakes that were proposed for the axisymmetric case are used in the current investigation, then there is good agreement between the two cases in the variation of the length scales with boundary-layer separation angle. The universal Strouhal number previously proposed for axisymmetric bodies is derived for the two-dimensional bodies under investigation and is found to remain a constant for the different bodies, but at a different numerical value from that found for the axisymmetric bodies.

Flow Separation Control in an Annular to Conical Diffuser Using Two-Dimensional and Three-Dimensional Wall Steps

2013 ◽  
Vol 135 (4) ◽  
Author(s):  
Kin Pong Lo ◽  
Christopher J. Elkins ◽  
John K. Eaton
Keyword(s):  
Boundary Layer ◽  
Pressure Gradient ◽  
Flow Control ◽  
Separation Bubble ◽  
Adverse Pressure Gradient ◽  
Boundary Layer Separation ◽  
Core Flow ◽  
Layer Separation ◽  
Wall Boundary Layer ◽  
Wall Boundary

Conical diffusers are often installed downstream of a turbomachine with a central hub. Previous studies showed that nonstreamlined hubs had extended separated wakes that reduced the adverse pressure gradient in the diffuser. Active flow control techniques can rapidly close the central separation bubble, but this restores the adverse pressure gradient, which can cause the outer wall boundary layer to separate. The present study focuses on the use of a step-wall diffuser to stabilize the wall boundary layer separation in the presence of core flow control. Three-component mean velocity data for a set of conical diffusers were acquired using magnetic resonance velocimetry. The results showed the step-wall diffuser stabilized the wall boundary layer separation by fixing its location. An axisymmetric step separation bubble was formed. A step with a periodically varying height reduced the reattachment length of the step separation and allowed the diffuser to be shortened. The step-wall diffuser was found to be robust in a range of core flow velocity profiles. The minimum distance between the core flow control mechanism and the step-wall diffuser as well as the minimum length of the step were determined.

Flow Control in an Aggressive Inter-Turbine Duct Using Low Profile Vortex Generators

2012 ◽  
Author(s):  
Yanfeng Zhang ◽  
Shuzhen Hu ◽  
Xue Feng Zhang ◽  
Michael Benner ◽  
Edward Vlasic
Keyword(s):  
Boundary Layer ◽  
Radial Pressure ◽  
Boundary Layer Separation ◽  
Vortex Generators ◽  
Flow Structures ◽  
Streamwise Vortices ◽  
Streamwise Vorticity ◽  
Layer Separation ◽  
Low Profile ◽  
Flow Mechanisms

This paper presents the experimental investigation of the flow in an aggressive inter-turbine duct (AITD). The goal is to improve the understanding of the flow mechanisms within the AITD and of the underlying physics of low-profile vortex generators (LPVGs). The flow structures in the AITD are dominated by counter-rotating vortices and boundary layer separations in both the casing and hub regions. At the first bend of the AITD, the casing boundary layer separates in a 3D mode because of the upstream wakes; this is followed by a massive 2D boundary layer separation. Due to the effect of the radial pressure gradient at the first bend, the streamwise vorticity generated by the casing 3D separation stays close to the casing endwall, and later mixes with the casing counter-rotating vortices formed at the second bend. By using LPVGs with different configurations installed on the casing, the casing boundary layer separation is significantly reduced. The streamwise vortices generated by the LPVGs have the potential to generate another pair of counter-rotating vortices at the AITD second bend, which help to delay/prevent the boundary layer separation. Therefore, the total pressure loss in the AITD was significantly reduced.

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