Numerical Investigation of the Origin of Losses in the Rotor Hub Region of a Multistage Axial Compressor

2013 ◽  
Author(s):  
Simon Herve ◽  
Oliver Reutter ◽  
Mark Wieler ◽  
Eberhard Nicke
Keyword(s):  
Air Flow ◽  
Axial Compressor ◽  
Local Maximum ◽  
Suction Side ◽  
Blade Height ◽  
Future Design ◽  
Flow Losses ◽  
Inflow Condition ◽  
Endwall Contouring ◽  
Secondary Air

Endwall losses and secondary air flow are considered to be responsible for a significant part of the flow losses in compressors. Their reduction can be achieved by 3D blade design and non-axisymmetric endwalls. In order to evaluate the potential of both effects, an analysis of secondary air flow and the origin of losses is realized. This paper presents multiple numerical simulations to determine the predominant phenomena at the origin of losses in the hub region of the last rotor of the Rig 250, a 4-stage compressor with cantilevered stators and rotor tip clearances. In a first study (I), an inviscid endwall condition at the hub of rotor 4 has been investigated. This condition strongly reduces the secondary air flow from the pressure side to the suction side and shows a significant reduction of the losses in the hub region. But the typical loss distribution over the blade height with a local maximum between 5 and 15 % of the blade height is not changed. Through this study the losses generated by the endwall boundary layer and the resulting secondary air flow are evaluated. Moreover, the potential for endwall contouring and 3D blading in the hub region is estimated, which can be used in future design studies. In the second study (II), ideal radial distributions of the velocity and of the inflow angles at the inlet of the rotor 4 are set. The results show the dependencies between the inflow condition and the loss production in the blade passage near the endwall. These studies sets the theoretical maximal potential for improvement techniques, like endwall contouring or the modification of the upstream stator.

A numerical study on the unsteady effect of axial spacing on the performance in a contra-rotating axial compressor

2016 ◽  
Vol 231 (14) ◽  
pp. 2598-2609 ◽  
Author(s):  
Xiaochen Mao ◽  
Bo Liu
Keyword(s):  
Aerodynamic Force ◽  
Numerical Study ◽  
Pressure Fluctuations ◽  
Axial Compressor ◽  
Maximum Amplitude ◽  
Local Maximum ◽  
Leading Edge ◽  
Suction Side ◽  
Pressure Surface ◽  
Unsteady Effects

Unsteady numerical simulations are conducted to investigate the unsteady effects of axial spacing on the performance of a contra-rotating axial compressor. The results show that the stage efficiency is dominant by unsteady effects between two rotors at lower axial gap ranges. As the axial spacing is increased, the variation of aerodynamic force is different for the two rotors. As a whole, the oscillation on the pressure surface is much stronger than that on the suction side in rotor1. For rotor2, however, the local maximum amplitude is just located at the blade leading edge, especially near the tip region. Additionally, the maximum amplitude of the pressure fluctuations generally decreases with an increase of axial spacing. The dominating frequency is different for monitors located at different positions and varies with the increasing of axial gaps. As the axial gap is increased, the potential effects decay in the process of propagating. Meanwhile, the incoming wakes are mixed out more sufficiently which would reduce the fluctuations at leading edge of rotor2. Therefore, a proper axial spacing should be chosen in the design process of a contra-rotating axial compressor considering both the performance and structure.

Numerical Investigation on the Effect of Vortex Generator on Axial Compressor Performance

2014 ◽  
Author(s):  
Ruchika Agarwal ◽  
Anand Dhamarla ◽  
Sridharan R. Narayanan ◽  
Shraman N. Goswami ◽  
Balamurugan Srinivasan
Keyword(s):  
Cross Flow ◽  
Axial Compressor ◽  
Vortex Generator ◽  
Side Surface ◽  
Suction Side ◽  
Test Case ◽  
Stall Margin ◽  
Layer Flow ◽  
Flow Effects ◽  
End Wall

The performance of the compressor blade is considerably influenced by secondary flow effects, like the cross flow on the end wall as well as corner flow separation between the wall and the blade. The present work is focused on the studying the effects of Vortex Generator (VG) on NASA Rotor 37 test case using Computational Fluid Dynamics (CFD). VG helps in controlling the inception of the stall by generating vortices and energizes the low momentum boundary layer flow which enhances the rotor performance. Three design configuration namely, Counter-rotating, Co-rotating and Plow configuration VG are selected based on the improved aerodynamic performance discussed in reference [1]. These VG are located at 90% span and 42% chord on suction side surface of the blade. Among the three configurations, the first configuration has greater impact on the end wall cross flow and flow deflection which resulted in enhanced numerical stall margin of 5.4% from baseline. The reasons for this numerical stall margin improvement are discussed in detail.

Model-Based Analysis of Transient Behavior of Large Scale CFB Boilers

2003 ◽  
Author(s):  
Ari Kettunen ◽  
Timo Hyppa¨nen ◽  
Ari-Pekka Kirkinen ◽  
Esa Maikkola
Keyword(s):  
Flow Rate ◽  
Large Scale ◽  
Air Flow ◽  
Model Parameters ◽  
Air Flow Rate ◽  
Process Data ◽  
Cfb Boiler ◽  
Flow Rates ◽  
Load Change ◽  
Secondary Air

The main objective of this study was to investigate the load change capability and effect of the individual control variables, such as fuel, primary air and secondary air flow rates, on the dynamics of large-scale CFB boilers. The dynamics of the CFB process were examined by dynamic process tests and by simulation studies. A multi-faceted set of transient process tests were performed at a commercial 235 MWe CFB unit. Fuel reactivity and interaction between gas flow rates, solid concentration profiles and heat transfer were studied by step changes of the following controllable variables: fuel feed rate, primary air flow rate, secondary air flow rate and primary to secondary air flow ratio. Load change performance was tested using two different types of tests: open and closed loop load changes. A tailored dynamic simulator for the CFB boiler was built and fine-tuned by determining the model parameters and by validating the models of each process component against measured process data of the transient test program. The know-how about the boiler dynamics obtained from the model analysis and the developed CFB simulator were utilized in designing the control systems of three new 262 MWe CFB units, which are now under construction. Further, the simulator was applied for the control system development and transient analysis of the supercritical OTU CFB boiler.

Experimental Characterization of the Evolution of Global Flow Structure in the Passage of an Axial Compressor

2021 ◽  
Author(s):  
Ayush Saraswat ◽  
Subhra Shankha Koley ◽  
Joseph Katz
Keyword(s):  
Flow Structure ◽  
Rotor Blade ◽  
Incidence Angle ◽  
Substantial Reduction ◽  
Axial Compressor ◽  
Suction Side ◽  
Rotor Wake ◽  
Tip Leakage ◽  
Blade Tip

Abstract Ongoing experiments conducted in a one-and-half stages axial compressor installed in the JHU refractive index-matched facility investigate the evolution of flow structure across blade rows. After previously focusing only on the rotor tip region, the present stereo-PIV (SPIV) measurements are performed in a series of axial planes covering an entire passage across the machine, including upstream of the IGV, IGV-rotor gap, rotor-stator gap, and downstream of the stator. The measurements are performed at flow rates corresponding to pre-stall condition and best efficiency point (BEP). Data are acquired for various rotor-blade orientations relative to the IGV and stator blades. The results show that at BEP, the wakes of IGV and rotor are much more distinct and the wake signatures of one row persists downstream of the next, e.g., the flow downstream of the stator is strongly affected by the rotor orientation. In contrast, under pre-stall conditions, the rotor orientation has minimal effect on the flow structure downstream of the stator. However, the wakes of the stator blades, where the axial momentum is low, are now wider. For both conditions, the flow downstream of the rotor is characterized by two regions of axial momentum deficit in addition to the rotor wake. A deficit on the pressure side of the rotor wake tip is associated with the tip leakage vortex (TLV) of the previous rotor blade, and is much broader at pre-stall condition. A deficit on the suction side of the rotor wake near the hub appears to be associated with the hub vortex generated by the neighboring blade, and is broader at BEP. At pre-stall, while the axial momentum upstream of the rotor decreases over the entire tip region, it is particularly evident near the rotor blade tip, where the instantaneous axial velocity becomes intermittently negative. Downstream of the rotor, there is a substantial reduction in mean axial momentum in the upper half of the passage, concurrently with an increase in the circumferential velocity. Consequently, the incidence angle upstream of the stator increases in certain regions by up to 30 degrees. These observations suggest that while the onset of the stall originates from the rotor tip flow, one must examine its impact on the flow structure in the stator passage as well.

Non-Axisymmetric Endwall Contouring in a Linear Compressor Cascade

2020 ◽  
Author(s):  
Yuchen Ma ◽  
Jinfang Teng ◽  
Mingmin Zhu ◽  
Xiaoqing Qiang
Keyword(s):  
Pressure Loss ◽  
Reverse Flow ◽  
Measurement Techniques ◽  
Suction Side ◽  
Limiting Factor ◽  
Blade Surface ◽  
Compressor Cascade ◽  
Linear Compressor ◽  
Endwall Contouring ◽  
Linear Compressor Cascade

Abstract Modern axial compressors are designed to be highly loaded in terms of aerodynamics, which can lead to challenges of increasing the compressor efficiency. Losses associated with secondary flow effects are well known to be the major limiting factor of improving the compressor performance. In this study, non-axisymmetric endwall contouring in a linear compressor cascade was generated through the optimization process. Combined with numerical simulation, wind tunnel tests on linear cascades with flat and contoured endwall were performed with various measurement techniques at the design and off-design conditions. The simulation results show that optimal endwall design can provide 3.08% reduction of the total pressure loss at the design condition. The reduction of pressure loss obtained is mainly below 24%span with the size of the high loss region being effectively reduced. At off-design condition, the numerical benefit of the endwall contouring is found less pronounced. The discrepancy is spotted between simulation and experiments. The experimental pressure loss reduction is mainly below 18% at ADP. And the pressure loss for the CEW increases greatly at offdesign condition in experiments. Flow patterns revealed by numerical simulations show that the separation on the blade surface is mitigated with focus point disappearing, and reverse flow on the endwall near the suction side corner is moved away from the blade surface. CFD analysis indicates that the altered pressure distribution on the endwall accelerates the flow at the suction side corner and moves the reverse flow core further downstream. The weakened interaction between the corner vortex and tornado-like vortex from the endwall near the suction side corner is the main control mechanism of the CEW. The performance improvement in the linear compressor is mainly gained from it.

scholarly journals Investigation of Vortical Structures and Turbulence Characteristics in Corner Separation in an Axial Compressor Stator Using DDES

Energies ◽  
2020 ◽  
Vol 13 (9) ◽  
pp. 2123
Author(s):  
Jun Li ◽  
Jun Hu ◽  
Chenkai Zhang
Keyword(s):  
Three Dimensional ◽  
Axial Compressor ◽  
Suction Side ◽  
Turbulence Energy ◽  
Separation Flow ◽  
Mechanism Analysis ◽  
Separation Region ◽  
Detached Eddy Simulation ◽  
Vortical Structures ◽  
Corner Separation

In order to investigate the flow structure and unsteady behavior of three-dimensional corner separation, a delayed detached-eddy simulation (DDES) method based on the Spalart–Allmaras (SA) model is performed on the third-stage stator of a multistage low-speed axial compressor. The stator simulation is validated by experiments before flow mechanism analysis. The complicated flow fields in the stator are then described step by step. Firstly, the structure and development process of vortices in corner separation flow are analyzed. Secondly, the velocity histogram of the monitor points in the mainstream and corner separation regions is obtained, and the velocity distribution of the corner separation region is discussed. Finally, Reynolds stress, Lumley anisotropy, turbulence energy spectra, and helicity density are discussed to understand the turbulence behavior of the corner separation flow in the stator. The results show that the corner separation appears at even the design condition and different kinds of vortical structures appear in the stator hub corner. The unsteadiness of corner separation flow is mainly reflected in the separation on the suction side of the blade and the wake shedding. Turbulence anisotropy and energy backscatter are found to be dominant in the separation region, which is correlated to the high shear stress.

The Effects of Air Flow Rates, Secondary Air Inlet Geometry, Fuel Type, and Operating Mode on the Performance of Gasifier Cookstoves

2016 ◽  
Vol 50 (17) ◽  
pp. 9754-9763 ◽  
Author(s):  
Jessica Tryner ◽  
James W. Tillotson ◽  
Marc E. Baumgardner ◽  
Jeffrey T. Mohr ◽  
Morgan W. DeFoort ◽  
...  
Keyword(s):  
Air Flow ◽  
Operating Mode ◽  
Fuel Type ◽  
Flow Rates ◽  
Air Inlet ◽  
Inlet Geometry ◽  
Secondary Air

Numerical Simulation of Effects of Tip Geometry on the Performance of an Axial Compressor

2012 ◽  
Author(s):  
Hongwei Ma ◽  
Jun Zhang
Keyword(s):  
Mass Flow ◽  
Tangential Force ◽  
Axial Compressor ◽  
Pressure Rise ◽  
Leading Edge ◽  
Suction Side ◽  
Leakage Flow ◽  
Base Line ◽  
Compressor Rotor ◽  
Blade Tip

The purpose of this paper is to investigate numerically the effects of the tip geometry on the performance of an axial compressor rotor. There are three case studies which are compared with the base line tip geometry. 1) baseline (flat tip); 2) Cavity (tip with a cavity); 3) SSQA (suction side squealer tip) and 4) SSQB (modified suction side squealer tip). The case of SSQB is a combination of suction side squealer tip and the cavity tip. From leading edge to 10% chord, the tip has a cavity. From 10% chord to trailing edge, the tip has a suction side squealer. The numerical results of 2) show that the cavity tip leads to lower leakage mass flow and greater loss in tip gap and the rotor passage. The loading near the blade tip is lower than the baseline, thus the tangential force of the blade is lower. It leads to lower pressure rise than the baseline. The performance of the compressor for the tip with cavity is worse than the baseline. The results of 3) show that the higher curvature of the suction side squealer increases the loading of the blade and the tangential blade force. With the suction side squealer tip, the leakage flow experiences two vena contractor thus the mass of the leakage flow is reduced which is benefit for the performance of the compressor. The loss in the tip gap is lower than baseline. The performance is better than the baseline with greater pressure rise of the rotor, smaller leakage mass flow and lower averaged loss. For the case the SSQB, the leakage mass flow is lower than the SSQA and the loss in the tip gap and the rotor passage is greater than SSQA. The performance of the case of the SSQB is worse than the case of SSQA.

Visualizations of Flow Structures in the Rotor Passage of an Axial Compressor at the Onset of Stall

2017 ◽  
Vol 139 (4) ◽  
Author(s):  
Huang Chen ◽  
Yuanchao Li ◽  
David Tan ◽  
Joseph Katz
Keyword(s):  
High Speed ◽  
Large Scale ◽  
Incidence Angle ◽  
Axial Compressor ◽  
Leading Edge ◽  
Suction Side ◽  
Stereoscopic Particle Image Velocimetry ◽  
High Speed Imaging ◽  
Vortical Structures ◽  
Flow Phenomena

Experiments preformed in the JHU refractive index matched facility examine flow phenomena developing in the rotor passage of an axial compressor at the onset of stall. High-speed imaging of cavitation performed at low pressures qualitatively visualizes vortical structures. Stereoscopic particle image velocimetry (SPIV) measurements provide detailed snapshots and ensemble statistics of the flow in a series of meridional planes. At prestall condition, the tip leakage vortex (TLV) breaks up into widely distributed intermittent vortical structures shortly after rollup. The most prominent instability involves periodic formation of large-scale backflow vortices (BFVs) that extend diagonally upstream, from the suction side (SS) of one blade at midchord to the pressure side (PS) near the leading edge of the next blade. The 3D vorticity distributions obtained from data recorded in closely spaced planes show that the BFVs originate form at the transition between the high circumferential velocity region below the TLV center and the main passage flow radially inward from it. When the BFVs penetrate to the next passage across the tip gap or by circumventing the leading edge, they trigger a similar phenomenon there, sustaining the process. Further reduction in flow rate into the stall range increases the number and size of the backflow vortices, and they regularly propagate upstream of the leading edge of the next blade, where they increase the incidence angle in the tip corner. As this process proliferates circumferentially, the BFVs rotate with the blades, indicating that there is very little through flow across the tip region.

Calculation of the Parameters of Combustion Products of Sewage Sludge

2018 ◽  
Vol 22 (6) ◽  
pp. 54-57
Author(s):  
A.V. Demin ◽  
R.Ya. Dyganova ◽  
V.P. Shipkov ◽  
R.R. Valiev
Keyword(s):  
Sewage Sludge ◽  
Phase Equilibria ◽  
Air Flow ◽  
Combustion Products ◽  
Flow Rates ◽  
Optimal Ratio ◽  
Secondary Air

The problems associated with the use of existing thermal installations for the incineration of sewage sludge and the design of new structures are considered. The results obtained by calculating the chemical and phase equilibria are presented. Recommended optimal ratio of primary and secondary air flow rates with its step-by-step approach.

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