Modeling Unsteady Transition and Its Effects on Profile Loss

1990 ◽  
Vol 112 (4) ◽  
pp. 691-701 ◽  
Author(s):  
H. P. Hodson
Keyword(s):  
Turbine Blades ◽  
Transition Process ◽  
Frequency Parameter ◽  
Reduced Frequency ◽  
Boundary Layer Development ◽  
Blade Row ◽  
Wake Interactions ◽  
Unsteady Inflow ◽  
Layer Development ◽  
Profile Loss

This paper considers the effects of wake interactions on the transition processes of turbomachine blade boundary layers. A simple model of unsteady transition is proposed, which is then used to identify a relationship between a new reduced frequency parameter and the profile loss of a blade row that is subjected to unsteady inflow. The value of this new parameter is also used to identify the nature of the boundary layer development on the blade surfaces. The influence of other parameters on the transition process is also discussed. The model is then extended to deal with the more general case. The validity of the models is demonstrated by a comparison with a correlation of the effects of wake-generated unsteadiness on profile loss that was originally proposed by Speidel. The effects of unsteady inflow on four idealized turbine blades are considered.

Compressor Blade Boundary Layers: Part 2 — Measurements With Incident Wakes

1989 ◽  
Author(s):  
Y. Dong ◽  
N. A. Cumpsty
Keyword(s):  
Boundary Layer ◽  
Boundary Layers ◽  
Transition Process ◽  
Compressor Blade ◽  
Momentum Thickness ◽  
Trailing Edge ◽  
Boundary Layer Development ◽  
Blade Row ◽  
Layer Development

This paper follows directly from Part I** by the same authors and describes measurements of the boundary layer on a supercritical-type compressor blade with wakes from a simulated moving upstream blade row convected through the passage. (The blades and the test facilities togehter with the background are described in Part I.) The results obtained with the wakes are compared to those with none for both low and high levels of inlet turbulence. The transition process and boundary layer development is very different in each case though the overall momentum thickness at the trailing edge is fairly similar. None of the models for transition is satisfactory when this is initiated by moving wakes.

Compressor Blade Boundary Layers: Part 2—Measurements With Incident Wakes

1990 ◽  
Vol 112 (2) ◽  
pp. 231-240 ◽  
Author(s):  
Y. Dong ◽  
N. A. Cumpsty
Keyword(s):  
Boundary Layer ◽  
Boundary Layers ◽  
Transition Process ◽  
Compressor Blade ◽  
Momentum Thickness ◽  
Trailing Edge ◽  
Boundary Layer Development ◽  
Blade Row ◽  
Layer Development

This paper follows directly from Part 1 by the same authors and describes measurements of the boundary layer on a supercritical-type compressor blade with wakes from a simulated moving upstream blade row convected through the passage. (The blades and the test facilities together with the background are described in Part 1). The results obtained with the wakes are compared to those with none for both low and high levels of inlet turbulence. The transition process and boundary layer development are very different in each case, though the overall momentum thickness at the trailing edge is fairly similar. None of the models for transition is satisfactory when this is initiated by moving wakes.

Experimental Study of the Effect of Periodic Unsteady Wake Flow on Boundary Layer Development, Separation, and Reattachment Along the Surface of a Low Pressure Turbine Blade

2004 ◽  
Vol 126 (4) ◽  
pp. 663-676 ◽  
Author(s):  
M. T. Schobeiri ◽  
B. O¨ztu¨rk
Keyword(s):  
Boundary Layer ◽  
Separation Bubble ◽  
Wake Flow ◽  
Suction Surface ◽  
Low Pressure Turbine ◽  
Reduced Frequency ◽  
Boundary Layer Development ◽  
Unsteady Wake ◽  
Unsteady Wake Flow ◽  
Layer Development

The paper experimentally studies the effects of periodic unsteady wake flow on boundary layer development, separation and reattachment along the suction surface of a low pressure turbine blade. The experimental investigations were performed on a large scale, subsonic unsteady turbine cascade research facility at the Turbomachinery Performance and Flow Research Laboratory (TPFL), Texas A&M University. The experiments were carried out at a Reynolds number of 110,000 (based on suction surface length and exit velocity) with a free-stream turbulence intensity of 1.9%. One steady and two different unsteady inlet flow conditions with the corresponding passing frequencies, wake velocities, and turbulence intensities were investigated. The reduced frequencies cover the entire operating range of LP turbines. In addition to the unsteady boundary layer measurements, blade surface measurements were performed at the same Reynolds number. The surface pressure measurements were also carried out at one steady and two periodic unsteady inlet flow conditions. The results presented in ensemble-averaged, and the contour plot forms help to understand the physics of the separation phenomenon under periodic unsteady wake flow. It was found that the suction surface displayed a strong separation bubble for these three different reduced frequencies. For each condition, the locations and the heights defining the separation bubble were determined by carefully analyzing and examining the pressure and the mean velocity profile data. The location of boundary layer separation was independent of the reduced frequency level. However, the extent of the separation was strongly dependent on the reduced frequency level. Once the unsteady wake started to penetrate into the separation bubble, the turbulent spot produced in the wake paths caused a reduction of the separation bubble height.

Experimental Study of the Effect of Periodic Unsteady Wake Flow on Boundary Layer Development, Separation, and Re-Attachment Along the Surface of a Low Pressure Turbine Blade

2004 ◽  
Author(s):  
M. T. Schobeiri ◽  
B. O¨ztu¨rk
Keyword(s):  
Boundary Layer ◽  
Separation Bubble ◽  
Wake Flow ◽  
Suction Surface ◽  
Low Pressure Turbine ◽  
Reduced Frequency ◽  
Boundary Layer Development ◽  
Unsteady Wake ◽  
Unsteady Wake Flow ◽  
Layer Development

The paper experimentally studies the effects of periodic unsteady wake flow on boundary layer development, separation and re-attachment along the suction surface of a low pressure turbine blade. The experimental investigations were performed on a large scale, subsonic unsteady turbine cascade research facility at Turbomachinery Performance and Flow Research Laboratory (TPFL), Texas A&M University. The experiments were carried out at a Reynolds number of 110,000 (based on suction surface length and exit velocity) with a free-stream turbulence intensity of 1.9%. One steady and two different unsteady inlet flow conditions with the corresponding passing frequencies, wake velocities, and turbulence intensities were investigated. The reduced frequencies cover the entire operating range of LP turbines. In addition to the unsteady boundary layer measurements, blade surface measurements were performed at the same Reynolds number. The surface pressure measurements were also carried out at one steady and two periodic unsteady inlet flow conditions. The results presented in ensemble-averaged, and the contour plot forms help to understand the physics of the separation phenomenon under periodic unsteady wake flow. It was found that the suction surface displayed a strong separation bubble for these three different reduced frequencies. For each condition, the locations and the heights defining the separation bubble were determined by carefully analyzing and examining the pressure and the mean velocity profile data. The location of boundary layer separation was independent of the reduced frequency level. However, the extent of the separation was strongly dependent on the reduced frequency level. Once the unsteady wake started to penetrate into the separation bubble, the turbulent spot produced in the wake paths caused a reduction of the separation bubble height.

The Influence of Heat Transfer Effects on Turbine Performance Characteristics

2006 ◽  
Author(s):  
A. G. Stamatis ◽  
K. Mathioudakis
Keyword(s):  
Heat Transfer ◽  
Turbine Blades ◽  
Performance Characteristics ◽  
Gas Temperature ◽  
Hot Gas ◽  
Turbine Performance ◽  
Boundary Layer Development ◽  
Development Change ◽  
Cooling Air ◽  
Layer Development

A method allowing the evaluation of the effects related to heat transfer to the turbine blades on its performance characteristics is presented. The effects investigated are the change of passage dimensions, resulting from heat transfer and the change in flow field, exhibited mainly as a different boundary layer development. Change of hot gas temperature combined with cooling air temperature and possibly flow rate, result in a change of the temperature of the blade material, leading to dimension changes, because of the thermal expansion (dilatation). The changes in dimensions have a direct effect on turbine performance. An immediate consequence is a modification of the mass flow characteristic, due to a change of the throat area. Heat transfer also influences the properties of the gas flowing through the passage and in particular the characteristics of the boundary layers developing on the nozzle vanes and hub, tip endwals. Change of the thickness of this layer results in a change of blockage through the passage, a fact that influences directly the turbine flow function. The influence of both effects on turbine performance is studied. The study is performance oriented, aiming to the derivation of simplified models, which can be introduced in engine cycle decks.

scholarly journals Realizability in Turbulence Modelling for Turbomachinery CFD

1999 ◽  
Author(s):  
Joan G. Moore ◽  
John Moore
Keyword(s):  
Turbulent Viscosity ◽  
Turbulence Models ◽  
Leading Edge ◽  
Pressure Gradients ◽  
Normal Stresses ◽  
Boundary Layer Development ◽  
Profile Losses ◽  
Blade Row ◽  
Turbine Cascades ◽  
Layer Development

It is obvious that the Reynolds normal stresses uu¯ should always be positive in all directions, i.e. the computed turbulence stresses should be realizable. However, the commonly used two-equation turbulence models do not incorporate realizability. They take the turbulent viscosity as cμk2/ε with cμ a constant, and frequently generate negative normal stresses far from walls in the nominally inviscid sections of turbomachinery flows. Pressure gradients due to leading edge stagnation and blade turning create an inviscid strain field. These strains cause the calculation of negative normal stresses over significant portions of the flow field. The result can be erroneous increases in turbulence kinetic energy upstream of the leading edge by a factor of ten or more. This erroneous turbulence is then convected around the blade and through the blade row, significantly affecting the computed boundary layer development and profile losses. Frequently the problem of overproduction is avoided by using artificially high values of the dissipation, ε, at the inlet. But this incorrect procedure is not needed when realizability is incorporated in the turbulence model. The paper reviews some methods and models which ensure realizability in two-equation turbulence models. The extent of the problem and its solution are illustrated with examples from compressor and turbine cascades.

Effects of periodic wakes on boundary layer development on an ultra-high-lift low pressure turbine airfoil

2016 ◽  
Vol 231 (1) ◽  
pp. 25-38 ◽  
Author(s):  
Xingen Lu ◽  
Yanfeng Zhang ◽  
Wei Li ◽  
Shuzhen Hu ◽  
Junqiang Zhu
Keyword(s):  
Boundary Layer ◽  
Transition Process ◽  
Low Pressure ◽  
Suction Surface ◽  
High Lift ◽  
Low Pressure Turbine ◽  
Turbulent Transition ◽  
Boundary Layer Development ◽  
Unsteady Wake ◽  
Layer Development

The laminar-turbulent transition process in the boundary layer is of significant practical interest because the behavior of this boundary layer largely determines the overall efficiency of a low pressure turbine. This article presents complementary experimental and computational studies of the boundary layer development on an ultra-high-lift low pressure turbine airfoil under periodically unsteady incoming flow conditions. Particular emphasis is placed on the influence of the periodic wake on the laminar-turbulent transition process on the blade suction surface. The measurements were distinctive in that a closely spaced array of hot-film sensors allowed a very detailed examination of the suction surface boundary layer behavior. Measurements were made in a low-speed linear cascade facility at a freestream turbulence intensity level of 1.5%, a reduced frequency of 1.28, a flow coefficient of 0.70, and Reynolds numbers of 50,000 and 100,000, based on the cascade inlet velocity and the airfoil axial chord length. Experimental data were supplemented with numerical predictions from a commercially available Computational Fluid Dynamics code. The wake had a significant influence on the boundary layer of the ultra-high-lift low pressure turbine blade. Both the wake’s high turbulence and the negative jet behavior of the wake dominated the interaction between the unsteady wake and the separated boundary layer on the suction surface of the ultra-high-lift low pressure turbine airfoil. The upstream unsteady wake segments convecting through the blade passage behaved as a negative jet, with the highest turbulence occurring above the suction surface around the wake center. Transition of the unsteady boundary layer on the blade suction surface was initiated by the wake turbulence. The incoming wakes promoted transition onset upstream, which led to a periodic suppression of the separation bubble. The loss reduction was a compromise between the positive effect of the separation reduction and the negative effect of the larger turbulent-wetted area after reattachment due to the earlier boundary layer transition caused by the unsteady wakes. It appeared that the successful application of ultra-high-lift low pressure turbine blades required additional loss reduction mechanisms other than “simple” wake-blade interaction.

Aerodynamic Blade Row Interactions in an Axial Compressor—Part I: Unsteady Boundary Layer Development

2004 ◽  
Vol 126 (1) ◽  
pp. 35-44 ◽  
Author(s):  
Ronald Mailach ◽  
Konrad Vogeler
Keyword(s):  
Boundary Layer ◽  
Layer Structure ◽  
Experimental Investigations ◽  
Turbulence Structure ◽  
Unsteady Boundary Layer ◽  
Time Resolved ◽  
Boundary Layer Development ◽  
Blade Row ◽  
Operating Points ◽  
Layer Development

This two-part paper presents experimental investigations of unsteady aerodynamic blade row interactions in the first stage of the four-stage low-speed research compressor of Dresden. Both the unsteady boundary layer development and the unsteady pressure distribution of the stator blades are investigated for several operating points. The measurements were carried out on pressure side and suction side at midspan. In Part I of the paper the investigations of the unsteady boundary layer behavior are presented. The experiments were carried out using surface-mounted hot-film sensors. Additional information on the time-resolved flow between the blade rows were obtained with a hot-wire probe. The unsteady boundary layer development is strongly influenced by the incoming wakes. Within the predominantly laminar boundary layer in the front part of the blade a clear response of the boundary layer to the velocity and turbulence structure of the incoming wakes can be observed. The time-resolved structure of the boundary layer for several operating points of the compressor is analyzed in detail. The topic “calmed regions,” which can be coupled to the wake passing, is discussed. As a result an improved description of the complex boundary layer structure is given.

Boundary Layer Development on a High-Lift LP Turbine Profile Under Passing-Wakes Conditions

2009 ◽  
Author(s):  
Francesca Satta ◽  
Daniele Simoni ◽  
Marina Ubaldi ◽  
Pietro Zunino ◽  
Francesco Bertini
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Transition Process ◽  
Operating Conditions ◽  
High Lift ◽  
Layer Interaction ◽  
Boundary Layer Development ◽  
Boundary Layer Interaction ◽  
Lp Turbine ◽  
Layer Development

The boundary layer development on the suction side of a high-lift LP turbine profile has been experimentally investigated under steady and unsteady flow conditions in the range of Reynolds numbers between 70000 and 300000. Upstream wake periodic perturbations are generated by means of a tangential wheel of radial rods. The paper reports the results of the investigations performed for both steady and unsteady inflow cases (reduced frequency f+ = 0.62) for Re = 300000 and Re = 70000, representative of nominal and reduced Reynolds number operating conditions, respectively. A phase-locked ensemble-averaging technique has been employed to reconstruct the phase-averaged velocity and unresolved unsteadiness boundary layer profiles from the hotwire instantaneous velocities. Phase sequences of the boundary layer development, as well as time-space plots of velocity and unresolved unsteadiness in normal and streamwise directions highlight the complex wake/boundary layer interaction mechanism. While at the larger test Reynolds number the wake/boundary layer interaction does not substantially influence the transition process, at the lower test Reynolds number the boundary layer wake receptivity triggers the transition process, strongly attenuating the large separation bubble occurring at steady conditions.

Aerodynamic Blade Row Interactions in an Axial Compressor: Part I — Unsteady Boundary Layer Development

2003 ◽  
Author(s):  
Ronald Mailach ◽  
Konrad Vogeler
Keyword(s):  
Boundary Layer ◽  
Layer Structure ◽  
Experimental Investigations ◽  
Turbulence Structure ◽  
Unsteady Boundary Layer ◽  
Time Resolved ◽  
Boundary Layer Development ◽  
Blade Row ◽  
Operating Points ◽  
Layer Development

This two-part paper presents experimental investigations of unsteady aerodynamic blade row interactions in the first stage of the four-stage Low-Speed Research Compressor of Dresden. Both the unsteady boundary layer development and the unsteady pressure distribution of the stator blades are investigated for several operating points. The measurements were carried out on pressure side and suction side at midspan. In part I of the paper the investigations of the unsteady boundary layer behaviour are presented. The experiments were carried out using surface-mounted hot-film sensors. Additional information on the time-resolved flow between the blade rows were obtained with a hot-wire probe. The unsteady boundary layer development is strongly influenced by the incoming wakes. Within the predominantly laminar boundary layer in the front part of the blade a clear response of the boundary layer to the velocity and turbulence structure of the incoming wakes can be observed. The time-resolved structure of the boundary layer for several operating points of the compressor is analyzed in detail. The topic “calmed regions”, which can be coupled to the wake passing, is discussed. As a result an improved description of the complex boundary layer structure is given.

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