Comparing the Pressure Rise of Air and Supercritical Carbon Dioxide in Conical Diffusers

2012 ◽  
Author(s):  
B. Monje ◽  
D. Sánchez ◽  
R. Chacartegui ◽  
T. Sánchez ◽  
M. Savill ◽  
...  
Keyword(s):  
Carbon Dioxide ◽  
Boundary Layer ◽  
Supercritical Carbon Dioxide ◽  
Pressure Gradient ◽  
Pressure Rise ◽  
Adverse Pressure Gradient ◽  
Inlet Section ◽  
The Individual ◽  
Turbomachinery Design ◽  
Supercritical Carbon

The channels formed between adjacent blades in a turbine/compressor are nothing more than a variable section duct. Hence, the first step of turbomachinery design is to understand the physical processes experienced by a certain fluid when flowing through these nozzles and diffusers. In the main, nozzles are easier to understand since the fluid flows impelled by a favourable pressure gradient whereas for diffusers the flow has to face an adverse pressure gradient. This latter situation brings about the occurrence of stall (boundary layer detachment from the wall) which makes it more complicated to design and operate the component (both the individual stages and the entire compressor). It is thus essential to characterise the performance of diffusers of any type, which is influenced by several parameters such as geometry, Mach and Reynolds number, inlet total pressure and aspect of the boundary layer at the inlet section. Dolan and Runstadler generated very valuable information in 1973 (Pressure recovery performance of conical diffusers at high subsonic Mach numbers, NASA CR-2299) by providing performance maps for the flow of air in diffusers. This work is aimed at complementing the previous one by giving maps that apply to the flow of supercritical carbon dioxide in similar devices. By doing so, an important step towards the design of thermal turbomachinery specific of this singular fluid is taken.

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.

scholarly journals Impact of Fluid Substitution on the Performance of an Axial Compressor Blade Cascade Working with Supercritical Carbon Dioxide

2019 ◽  
Vol 142 (1) ◽  
Author(s):  
Carlos Tello ◽  
Alejandro Muñoz ◽  
David Sánchez ◽  
Timoleon Kipouros ◽  
Mark Savill
Keyword(s):  
Carbon Dioxide ◽  
Supercritical Carbon Dioxide ◽  
Axial Compressor ◽  
Computational Design ◽  
Compressor Blade ◽  
Working Fluid ◽  
Local Flow ◽  
Variable Boundary ◽  
Turbomachinery Design ◽  
Supercritical Carbon

Abstract Recent research on turbomachinery design and analysis for supercritical carbon dioxide (sCO2) power cycles has relied on computational fluid dynamics. This has produced a large number of works whose approach is mostly case-specific, rather than of general application to sCO2 turbomachinery design. As opposed to such approach, this work explores the aerodynamic performance of compressor blade cascades operating on air and supercritical CO2 with the main objective to evaluate the usual aerodynamic parameters of the cascade for variable boundary conditions and geometries, enabling “full” or “partial” similarity. The results present both the global performance of the cascades and certain features of the local flow (trailing edge and wake). The discussion also highlights the mechanical limitations of the analysis (forces exerted on the blades), which is the main restriction for applying similarity laws to extrapolate the experience gained through decades of work on air turbomachinery to the new working fluid. This approach is a step toward the understanding and appropriate formulation of a multi-objective optimization problem for the design of such turbomachinery components where sCO2 is used as the operating fluid. With this objective, the paper aims to identify and analyze what would be expected if a common description of such computational design problems similar to those where air is the working fluid were used.

scholarly journals Impact of Fluid Substitution on the Performance of an Axial Compressor Blade Cascade Working With Supercritical Carbon Dioxide

2019 ◽  
Author(s):  
Alejandro Muñoz ◽  
David Sánchez ◽  
Mark Savill ◽  
Timoleon Kipouros ◽  
Carlos Tello-Castillo
Keyword(s):  
Carbon Dioxide ◽  
Supercritical Carbon Dioxide ◽  
Axial Compressor ◽  
Computational Design ◽  
Compressor Blade ◽  
Working Fluid ◽  
Local Flow ◽  
Variable Boundary ◽  
Turbomachinery Design ◽  
Supercritical Carbon

Abstract Recent research on turbomachinery design and analysis for supercritical Carbon Dioxide (sCO2) power cycles has relied on Computational Fluid Dynamics. This has produced a large number of works whose approach is mostly case-specific, rather than of general application to sCO2 turbomachinery design. As opposed to such approach, this work explores the aerodynamic performance of compressor blade cascades operating on air and supercritical CO2 with the main objective to evaluate the usual aerodynamic parameters of the cascade for variable boundary conditions and geometries, enabling ‘full’ or ‘partial’ similarity. The results present both the global performance of the cascades and certain features of the local flow (trailing edge and wake). The discussion also highlights the mechanical limitations of the analysis (forces exerted on the blades), which is the main restriction to applying similarity laws to extrapolate the experience gained through decades of work on air turbomachinery to the new working fluid. This approach is a step towards the understanding and appropriate formulation of a multi-objective optimisation problem for the design of such turbomachinery components where sCO2 is used as the operating fluid. With this objective, the paper aims to identify and analyse what would be expected if a common description of such computational design problems similar to those where air is the working fluid were used.

Backpressure propagation mode and balance property in a rectangular duct

2018 ◽  
Vol 233 (4) ◽  
pp. 1472-1489
Author(s):  
Yubao He ◽  
Hongyan Huang ◽  
Daren Yu
Keyword(s):  
Boundary Layer ◽  
Pressure Gradient ◽  
Pressure Rise ◽  
Adverse Pressure Gradient ◽  
Force Balance ◽  
Propagation Mode ◽  
Rectangular Duct ◽  
Local Boundary ◽  
Starting Point ◽  
Balance Property

The backpressure propagation mode accompanied by shock-train evolution is investigated numerically in a rectangular duct with an open space. On this basis, the balance mechanism and parametric effects of heat transfer and skin friction for backpressure propagation are revealed to understand the nature of force competition better. As a result, the backpressure propagation mode can be classified into two different flow processes with increased backpressure. In addition, balance property mechanism reveals that both the momentum inside the boundary layer and the shear force which transfers the momentum from the outer core flow to boundary layer are combined to resist the adverse pressure gradient. Further, parametric effect indicates that varying wall temperatures and roughness heights lead to different degrees of changes in balance property. According to quantitative results, both wall temperature and roughness height decrease the local boundary-layer momentum at the starting point of original pressure rise and thus the local adverse pressure gradient wins the force competition. In the subsequently continuous flow, the adverse pressure gradient continues to propagate upstream and then is retarded gradually by the boundary layer with a fuller velocity profile until a new force balance is generated.

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.

Effect of Turbulence and Flow Distortion on the Performance of Conical Diffusers Operating on Supercritical Carbon Dioxide

2013 ◽  
Author(s):  
A. López ◽  
B. Monje ◽  
D. Sánchez ◽  
R. Chacartegui ◽  
T. Sánchez
Keyword(s):  
Carbon Dioxide ◽  
Supercritical Carbon Dioxide ◽  
Static Pressure ◽  
Pressure Rise ◽  
Working Fluid ◽  
Flow Distortion ◽  
Inlet Flow ◽  
Conical Diffuser ◽  
And Performance ◽  
Supercritical Carbon

A rapidly growing interest in the supercritical carbon dioxide power cycle has been observed in the last years due to the superb performance of this system in concentrated solar and nuclear applications; a sample of this interest is the number of technical publications submitted to Turbo Expo in the last couple of years. As active members of the supercritical carbon dioxide (SCO2) community, the authors of this work have lately studied the fundamentals of SCO2 flows. The approach followed has nevertheless been different to that of most researchers since it has concentrated on simple devices rather than on an entire turbomachinery. Thus, recent contributions by the authors have shown that major differences are to be expected when air and SCO2 diffuse through simple conical divergent ducts at subsonic speeds, most of which derive from the very different characteristics and performance of the boundary layer when adverse pressure gradients are faced. In particular, the effects of geometry (i.e. divergence angle) and aerodynamic blockage on the static pressure rise coefficient of such a conical diffuser have been reported by the authors in recent technical works. This work presents the effects of other aerodynamic features of the inlet flow to a conical diffuser on the capacity to convert kinetic energy into static pressure. Two flow features are studied: (i) the distortion of the inlet velocity distribution and (ii) the turbulence intensity of the inlet flow. A parallel analysis is developed for air and SCO2 showing that the effects of both distortion and turbulence on diffuser performance are sensitive to the working fluid of choice.

Self-preserving development within turbulent boundary layers in strong adverse pressure gradients

1965 ◽  
Vol 23 (4) ◽  
pp. 767-778 ◽  
Author(s):  
A. A. Townsend
Keyword(s):  
Boundary Layer ◽  
Pressure Gradient ◽  
Outer Part ◽  
Pressure Rise ◽  
Adverse Pressure Gradient ◽  
Pressure Gradients ◽  
Layer Model ◽  
Pressure Distributions ◽  
Two Layer Model ◽  
Local Parameters

The development of a turbulent boundary layer in a strong adverse pressure gradient can be described by the two-layer model proposed by Stratford (1959), in which the outer part of the flow is assumed to be unmodified by the pressure-rise and the inner part described by two local parameters, the surface stress and the pressure gradient. The description suggests that the modification of the original flow is in some sense self-preserving, and it is shown here that self-preserving development of the modification is consistent with the Reynolds equations of turbulent flow in particular pressure distributions. For these distributions, the predictions of the two-layer model are confirmed without any need to make the sharp and arbitrary distinction between the two parts of the boundary layer.

scholarly journals Effect of pressure on the Maillard reaction between ribose and cysteine in supercritical carbon dioxide

2010 ◽  
Vol 28 (No. 3) ◽  
pp. 192-201 ◽  
Author(s):  
H. Xu ◽  
W. He ◽  
K. Liu ◽  
Y. Gao
Keyword(s):  
Carbon Dioxide ◽  
Supercritical Carbon Dioxide ◽  
Aromatic Compounds ◽  
Model System ◽  
Base Catalysis ◽  
Reaction Products ◽  
Acid Base ◽  
Ph Decrease ◽  
The Individual ◽  
Supercritical Carbon

An aqueous ribose-cysteine model system, heated at 140&deg;C under supercritical carbon dioxide (SC-CO<sub>2</sub>) and supercritical nitrogen (SC-N<sub>2</sub>), was investigated with emphasis on the formation of volatile compounds. In general, SC-CO<sub>2</sub> facilitated the overall intermediates accumulation while suppressing the advanced stage of browning. 3-Methyl-1, 2-dithian-4-one increased with increasing SC-CO<sub>2</sub> pressure, and was always more concentrated than in the case of SC-N<sub>2</sub>-treatment. The formation of thiols, disulfides, and formyl substituted thiophenes was also promoted in SC-CO<sub>2</sub>-treated reaction products, while the effect of high pressure on the individual components followed different patterns. The reversible pH decrease and reinforced acid-base catalysis of 2, 3-enolisation by SC-CO<sub>2</sub> could attribute to the decreased browning and higher amounts of most intense meaty aromatic compounds. &nbsp;

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