The Experts below are selected from a list of 9282 Experts worldwide ranked by ideXlab platform
N A Cumpsty - One of the best experts on this subject based on the ideXlab platform.
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control of three dimensional separations in Axial Compressors by tailored boundary layer suction
Journal of Turbomachinery-transactions of The Asme, 2008Co-Authors: Semiu A Gbadebo, N A Cumpsty, T P HynesAbstract:One of the important ways of improving turbomachinery compressor performance is to control three-dimensional (3D) separations, which form over the suction surface and end wall corner of the blade passage. Based on the insights gained into the formation of these separations, this paper illustrates how an appropriately applied boundary layer suction of up to 0.7% of inlet mass flow can control and eliminate typical compressor stator hub corner 3D separation over a range of operating incidence. The paper describes, using computational fluid dynamics, the application of suction on the blade suction surface and end wall boundary layers and exemplifies the influence of end wall dividing streamline in initiating 3D separation in the blade passage. The removal of the separated region from the blade suction surface is confirmed by an experimental investigation in a compressor cascade involving surface flow visualization, surface static pressure, and exit loss measurements. The ensuing passage flow field is characterized by increased blade loading (static pressure difference between pressure and suction surface), enhanced average static pressure rise, significant loss removal, and a uniform exit flow. This result also enables the contribution of the 3D separation to the overall loss and passage blockage to be assessed.
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interaction of tip clearance flow and three dimensional separations in Axial Compressors
Journal of Turbomachinery-transactions of The Asme, 2007Co-Authors: Semiu A Gbadebo, N A Cumpsty, T P HynesAbstract:This paper considers the interaction of tip clearance flow with three-dimensional (3D) separations in the corner region of a compressor cascade. Three-dimensional numerical computations were carried out using ten levels of tip clearance, ranging from zero to 2.18% of blade chord. The 3D separations on the blade suction surface were largely removed by the clearance flow for clearance about 0.58% of chord. For this cascade, experimental results at zero and 1.7% chord tip clearance were used to assess the validity of the numerical predictions. The removal mechanism was associated with the suppression of the leading edge horseshoe vortex and the interaction of tip clearance flow with the endwall boundary layer, which develops into a secondary flow as it is driven towards the blade suction surface. Such interaction leads to the formation of a new 3D separation line on the endwall. The separation line forms the base of a separated stream surface which rolls up into the clearance vortex.
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interaction of tip clearance flow and three dimensional separations in Axial Compressors
ASME Turbo Expo 2006: Power for Land Sea and Air, 2006Co-Authors: Semiu A Gbadebo, N A Cumpsty, T P HynesAbstract:This paper considers the interaction of tip clearance flow with three-dimensional (3D) separations in the corner region of a compressor cascade. Three-dimensional numerical computations were carried out using ten levels of tip clearance, ranging from zero to 2.18% of blade chord. The 3D separations on the blade suction surface were largely removed by the clearance flow for clearance about 0.58% of chord. For this cascade, experimental results at zero and 1.7% chord tip clearance were used to assess the validity of the numerical predictions. The removal mechanism was associated with the suppression of the leading edge horseshoe vortex and the interaction of tip clearance flow with the endwall boundary layer, which develops into a secondary flow as it is drifted towards the blade suction surface. Such interaction leads to the formation of a new 3D separation line on the endwall. The separation line forms the base of a separated stream surface which rolls up into the clearance vortex.Copyright © 2006 by ASME
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three dimensional separations in Axial Compressors
Journal of Turbomachinery-transactions of The Asme, 2005Co-Authors: Semiu A Gbadebo, N A Cumpsty, T P HynesAbstract:Flow separations in the corner regions of blade passages are common. The separations are three dimensional and have quite different properties from the two-dimensional separations that are considered in elementary courses of fluid mechanics. In particular, the consequences for the flow may be less severe than the two-dimensional separation. This paper describes the nature of three-dimensional (3D) separation and addresses the way in which topological rules, based on a linear treatment of the Navier-Stokes equations, can predict properties of the limiting streamlines, including the singularities which form. The paper shows measurements of the flow field in a linear cascade of compressor blades and compares these to the results of 3D computational fluid dynamics (CFD). For corners without tip clearance, the presence of three-dimensional separation appears to be universal, and the challenge for the designer is to limit the loss and blockage produced. The CFD appears capable of predicting this.
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influence of surface roughness on three dimensional separation in Axial Compressors
Journal of Turbomachinery-transactions of The Asme, 2004Co-Authors: Semiu A Gbadebo, T P Hynes, N A CumpstyAbstract:Surface roughness on a stator blade was found to have a major effect on the three-dimensional (3D) separation at the hub of a single-stage low-speed Axial compressor. The change in the separation with roughness worsened performance of the stage. A preliminary study was carried out to ascertain which part of the stator suction surface and at what operating condition the flow is most sensitive to roughness. The results show that stage performance is extremely sensitive to surface roughness around the leading edge and peak-suction regions, particularly for flow rates corresponding to design and lower values. Surface flow visualization and exit loss measurements show that the size of the separation, in terms of spanwise and chordwise extent, is increased with roughness present. Roughness produced the large 3D separation at design flow coefficient that is found for smooth blades nearer to stall. A simple model to simulate the effect of roughness was developed and, when included in a 3D Navier-Stokes calculation method, was shown to give good qualitative agreement with measurements.
Hongwu Zhang - One of the best experts on this subject based on the ideXlab platform.
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Application of Fast Wavelet Analysis on Early Stall Warning in Axial Compressors
Journal of Thermal Science, 2019Co-Authors: Yang Liu, Li Fan, Hongwu ZhangAbstract:The timely detection of stall inception is of great significance for safe operation and stability control of Axial compressor. In the current study, a fast wavelet tool was selected to predict stall precursor in Axial Compressors with spike-type and modal-wave stall inception. Dynamic pressure was measured in the casing wall by using a collection of time-resolved pressure transducers with circumferential and chord-wise spatial resolution. Fast wavelet analysis with low frequency reconstruction results demonstrate that the initial inception can be detected 110 rotor revolutions prior to stall for modal-wave stall inception in a 1.5 stage Axial compressor. For spike-type stall inception, despite the failure of early stall warning via low frequency reconstruction, an increase amplitude frequency band of 0.2-0.8 blade passing frequency was identified using high frequency reconstruction in an isolated-rotor Axial compressor. Fast wavelet method can predict two kinds of stall inceptions simultaneously in advance and realize the early stall warning in Axial Compressors through a reasonable selection of reconstructed frequency.
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review of tip air injection to improve stall margin in Axial Compressors
Progress in Aerospace Sciences, 2019Co-Authors: Chaoqun Nie, Hongwu ZhangAbstract:Abstract The present paper provides a summary of investigations of the tip air injection, which has been studied for over 30 years to extend the stall margin in Axial flow Compressors. The review covers the design of injected parameters, understanding of stability-enhancing mechanism, application of active control, and self-recirculation based on tip air injection. First, the injected parameters that can influence the stability-enhancing capability are surveyed and classified. These include injected mass flow and momentum, structure, pitch and yaw angle, Axial location, and circumferential distribution. Next, the effect of tip air injection on the internal flow field is introduced; the action on the main stream flow or tip leakage flow depends on the injected moment ratio. Finally, the applications of active control with tip air injection and self-recirculating injection from a single-rotor to multi-stage Compressors are listed and discussed. The active control methods are based on the Moore–Greitzer model and online prediction of stall inception. This study aims to aid researchers who are working on stability enhancement with tip air injection in Compressors to improve their work. Moreover, considering that the regulation of injected mass flows or momentums is flexible, this study would facilitate the immediate application of the tip air injection in actual aero-engine Compressors.
T P Hynes - One of the best experts on this subject based on the ideXlab platform.
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modelling non uniform bleed in Axial Compressors
ASME Turbo Expo 2015: Turbine Technical Conference and Exposition, 2015Co-Authors: S D Grimshaw, Graham Pullan, T P HynesAbstract:The coupling between the bleed system and the flowfield of a downstream compressor stage is studied using two approaches.In the first, three-dimensional, full annulus, unsteady computations simulate the flow in a low speed research compressor with non-uniform bleed extraction. Comparisons with experimental data show that the flow prediction in the main annulus is accurate to within 0.005 of flow coefficient and 0.5° of flow angle. The CFD is then used to provide a description of flow within the bleed system itself.In the second approach, a two-dimensional mean radius model, similar to that adopted by Hynes and Greitzer in previous work on compressor stability, is used to simulate the response of the compressor to non-uniform bleed. This model is validated against experimental data for a single stage compressor and despite the inherent assumptions (two dimensional flow and simplified compressor response) provides a satisfactory prediction of the flow for preliminary design purposes with orders of magnitude less computational cost than full 3D CFD. The model is then used to investigate the effect of different levels of bleed non-uniformity and of varying the Axial distance between the bleed and the downstream stage. Reducing bleed non-uniformity and moving the stage away from the bleed slot are predicted to reduce the circumferential non-uniformity of the flow entering the stage.Copyright © 2015 by ASME
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control of three dimensional separations in Axial Compressors by tailored boundary layer suction
Journal of Turbomachinery-transactions of The Asme, 2008Co-Authors: Semiu A Gbadebo, N A Cumpsty, T P HynesAbstract:One of the important ways of improving turbomachinery compressor performance is to control three-dimensional (3D) separations, which form over the suction surface and end wall corner of the blade passage. Based on the insights gained into the formation of these separations, this paper illustrates how an appropriately applied boundary layer suction of up to 0.7% of inlet mass flow can control and eliminate typical compressor stator hub corner 3D separation over a range of operating incidence. The paper describes, using computational fluid dynamics, the application of suction on the blade suction surface and end wall boundary layers and exemplifies the influence of end wall dividing streamline in initiating 3D separation in the blade passage. The removal of the separated region from the blade suction surface is confirmed by an experimental investigation in a compressor cascade involving surface flow visualization, surface static pressure, and exit loss measurements. The ensuing passage flow field is characterized by increased blade loading (static pressure difference between pressure and suction surface), enhanced average static pressure rise, significant loss removal, and a uniform exit flow. This result also enables the contribution of the 3D separation to the overall loss and passage blockage to be assessed.
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interaction of tip clearance flow and three dimensional separations in Axial Compressors
Journal of Turbomachinery-transactions of The Asme, 2007Co-Authors: Semiu A Gbadebo, N A Cumpsty, T P HynesAbstract:This paper considers the interaction of tip clearance flow with three-dimensional (3D) separations in the corner region of a compressor cascade. Three-dimensional numerical computations were carried out using ten levels of tip clearance, ranging from zero to 2.18% of blade chord. The 3D separations on the blade suction surface were largely removed by the clearance flow for clearance about 0.58% of chord. For this cascade, experimental results at zero and 1.7% chord tip clearance were used to assess the validity of the numerical predictions. The removal mechanism was associated with the suppression of the leading edge horseshoe vortex and the interaction of tip clearance flow with the endwall boundary layer, which develops into a secondary flow as it is driven towards the blade suction surface. Such interaction leads to the formation of a new 3D separation line on the endwall. The separation line forms the base of a separated stream surface which rolls up into the clearance vortex.
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interaction of tip clearance flow and three dimensional separations in Axial Compressors
ASME Turbo Expo 2006: Power for Land Sea and Air, 2006Co-Authors: Semiu A Gbadebo, N A Cumpsty, T P HynesAbstract:This paper considers the interaction of tip clearance flow with three-dimensional (3D) separations in the corner region of a compressor cascade. Three-dimensional numerical computations were carried out using ten levels of tip clearance, ranging from zero to 2.18% of blade chord. The 3D separations on the blade suction surface were largely removed by the clearance flow for clearance about 0.58% of chord. For this cascade, experimental results at zero and 1.7% chord tip clearance were used to assess the validity of the numerical predictions. The removal mechanism was associated with the suppression of the leading edge horseshoe vortex and the interaction of tip clearance flow with the endwall boundary layer, which develops into a secondary flow as it is drifted towards the blade suction surface. Such interaction leads to the formation of a new 3D separation line on the endwall. The separation line forms the base of a separated stream surface which rolls up into the clearance vortex.Copyright © 2006 by ASME
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three dimensional separations in Axial Compressors
Journal of Turbomachinery-transactions of The Asme, 2005Co-Authors: Semiu A Gbadebo, N A Cumpsty, T P HynesAbstract:Flow separations in the corner regions of blade passages are common. The separations are three dimensional and have quite different properties from the two-dimensional separations that are considered in elementary courses of fluid mechanics. In particular, the consequences for the flow may be less severe than the two-dimensional separation. This paper describes the nature of three-dimensional (3D) separation and addresses the way in which topological rules, based on a linear treatment of the Navier-Stokes equations, can predict properties of the limiting streamlines, including the singularities which form. The paper shows measurements of the flow field in a linear cascade of compressor blades and compares these to the results of 3D computational fluid dynamics (CFD). For corners without tip clearance, the presence of three-dimensional separation appears to be universal, and the challenge for the designer is to limit the loss and blockage produced. The CFD appears capable of predicting this.
Semiu A Gbadebo - One of the best experts on this subject based on the ideXlab platform.
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control of three dimensional separations in Axial Compressors by tailored boundary layer suction
Journal of Turbomachinery-transactions of The Asme, 2008Co-Authors: Semiu A Gbadebo, N A Cumpsty, T P HynesAbstract:One of the important ways of improving turbomachinery compressor performance is to control three-dimensional (3D) separations, which form over the suction surface and end wall corner of the blade passage. Based on the insights gained into the formation of these separations, this paper illustrates how an appropriately applied boundary layer suction of up to 0.7% of inlet mass flow can control and eliminate typical compressor stator hub corner 3D separation over a range of operating incidence. The paper describes, using computational fluid dynamics, the application of suction on the blade suction surface and end wall boundary layers and exemplifies the influence of end wall dividing streamline in initiating 3D separation in the blade passage. The removal of the separated region from the blade suction surface is confirmed by an experimental investigation in a compressor cascade involving surface flow visualization, surface static pressure, and exit loss measurements. The ensuing passage flow field is characterized by increased blade loading (static pressure difference between pressure and suction surface), enhanced average static pressure rise, significant loss removal, and a uniform exit flow. This result also enables the contribution of the 3D separation to the overall loss and passage blockage to be assessed.
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interaction of tip clearance flow and three dimensional separations in Axial Compressors
Journal of Turbomachinery-transactions of The Asme, 2007Co-Authors: Semiu A Gbadebo, N A Cumpsty, T P HynesAbstract:This paper considers the interaction of tip clearance flow with three-dimensional (3D) separations in the corner region of a compressor cascade. Three-dimensional numerical computations were carried out using ten levels of tip clearance, ranging from zero to 2.18% of blade chord. The 3D separations on the blade suction surface were largely removed by the clearance flow for clearance about 0.58% of chord. For this cascade, experimental results at zero and 1.7% chord tip clearance were used to assess the validity of the numerical predictions. The removal mechanism was associated with the suppression of the leading edge horseshoe vortex and the interaction of tip clearance flow with the endwall boundary layer, which develops into a secondary flow as it is driven towards the blade suction surface. Such interaction leads to the formation of a new 3D separation line on the endwall. The separation line forms the base of a separated stream surface which rolls up into the clearance vortex.
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interaction of tip clearance flow and three dimensional separations in Axial Compressors
ASME Turbo Expo 2006: Power for Land Sea and Air, 2006Co-Authors: Semiu A Gbadebo, N A Cumpsty, T P HynesAbstract:This paper considers the interaction of tip clearance flow with three-dimensional (3D) separations in the corner region of a compressor cascade. Three-dimensional numerical computations were carried out using ten levels of tip clearance, ranging from zero to 2.18% of blade chord. The 3D separations on the blade suction surface were largely removed by the clearance flow for clearance about 0.58% of chord. For this cascade, experimental results at zero and 1.7% chord tip clearance were used to assess the validity of the numerical predictions. The removal mechanism was associated with the suppression of the leading edge horseshoe vortex and the interaction of tip clearance flow with the endwall boundary layer, which develops into a secondary flow as it is drifted towards the blade suction surface. Such interaction leads to the formation of a new 3D separation line on the endwall. The separation line forms the base of a separated stream surface which rolls up into the clearance vortex.Copyright © 2006 by ASME
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three dimensional separations in Axial Compressors
Journal of Turbomachinery-transactions of The Asme, 2005Co-Authors: Semiu A Gbadebo, N A Cumpsty, T P HynesAbstract:Flow separations in the corner regions of blade passages are common. The separations are three dimensional and have quite different properties from the two-dimensional separations that are considered in elementary courses of fluid mechanics. In particular, the consequences for the flow may be less severe than the two-dimensional separation. This paper describes the nature of three-dimensional (3D) separation and addresses the way in which topological rules, based on a linear treatment of the Navier-Stokes equations, can predict properties of the limiting streamlines, including the singularities which form. The paper shows measurements of the flow field in a linear cascade of compressor blades and compares these to the results of 3D computational fluid dynamics (CFD). For corners without tip clearance, the presence of three-dimensional separation appears to be universal, and the challenge for the designer is to limit the loss and blockage produced. The CFD appears capable of predicting this.
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influence of surface roughness on three dimensional separation in Axial Compressors
Journal of Turbomachinery-transactions of The Asme, 2004Co-Authors: Semiu A Gbadebo, T P Hynes, N A CumpstyAbstract:Surface roughness on a stator blade was found to have a major effect on the three-dimensional (3D) separation at the hub of a single-stage low-speed Axial compressor. The change in the separation with roughness worsened performance of the stage. A preliminary study was carried out to ascertain which part of the stator suction surface and at what operating condition the flow is most sensitive to roughness. The results show that stage performance is extremely sensitive to surface roughness around the leading edge and peak-suction regions, particularly for flow rates corresponding to design and lower values. Surface flow visualization and exit loss measurements show that the size of the separation, in terms of spanwise and chordwise extent, is increased with roughness present. Roughness produced the large 3D separation at design flow coefficient that is found for smooth blades nearer to stall. A simple model to simulate the effect of roughness was developed and, when included in a 3D Navier-Stokes calculation method, was shown to give good qualitative agreement with measurements.
Xinqian Zheng - One of the best experts on this subject based on the ideXlab platform.
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end wall boundary layers and blockages of multistage Axial Compressors under different conditions
Journal of Propulsion and Power, 2017Co-Authors: Xinqian Zheng, Heli YangAbstract:End-wall boundary layers and induced blockages are important factors for multistage Axial Compressors’ performance. This paper investigates hub and shroud end-wall boundary layers, and the corresponding blockages of a five-stage Axial compressor under different conditions. The results show that the hub displacement thickness increases from the front to rear stage, whereas the shroud displacement thickness remains almost the same. At the design point, the blockage increases from 2.4% for the front stage to 14.7% for the rear stage, which is dominated by the hub displacement thickness. Under different operating conditions of 100% speed, the blockage is almost the same for the front stage, but increases significantly for the rear stage from 6.0% at near choke to 22.2% at near surge. At peak-efficiency points of different rotational speeds, the blockage remains almost the same. The steady and unsteady results show almost the same trends of displacement thickness and blockage. Compared to unsteady simulations,...
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blade end treatment to improve the performance of Axial Compressors an overview
Progress in Aerospace Sciences, 2017Co-Authors: Xinqian ZhengAbstract:Abstract This paper reviews the literature published over the past 30 years on the blade-end treatment in Axial Compressors. The blade-end treatment reduces the endwall losses and extends the stable margin by modifying the blade shape near the endwall region with end-bend, end-dihedral and end-sweep flow control measures. The end-bend improves the overall performance by aligning the blade inlet/outlet to the flow stream direction. The end-dihedral reduces the blade force on the endwalls, while the end-sweep not only reduces the shock losses, but also controls the spanwise migration of the blade surface boundary layer. All these effects strongly influence the compressor performance by modifying the blading loading distribution in the streamwise or spanwise directions. However, the benefit of the endwall flow control comes with increased losses in the mainstream so there is a trade-off between the improved endwall region flows and the degraded mid-span flows. Thus, how to combine end-bend, end-dihedral and end-sweep to achieve the correct balance of loss distribution, appears to be the key to a successful three-dimensional compressor design.
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Influence of Tip Clearance on the Performance and Matching of Multistage Axial Compressors
Volume 2A: Turbomachinery, 2016Co-Authors: Xinqian Zheng, Heli YangAbstract:Tip clearance has great influence on the performance of multistage Axial Compressors including efficiency, pressure rise, mass flow, as well as matching. This paper reports a study into the influence of tip clearance on the performance and matching of a 5-stage Axial compressor by a numerical method. Different tip clearances from 0% to 5.0% span which represents the typical range of tip clearance in modern multistage Axial Compressors were simulated and analyzed. The results show that as tip clearance increases from 0% to 5.0% span, the choked mass flow decreases by about 21.8%, the peak pressure ratio decreases by about 43.1% and the peak efficiency decreases about 14.3 percents. As tip clearance increases, the efficiency of the whole compressor decreases in a parabolic manner not linearly as previous suggested, which is partially attributable to the cantilevered stators considered in this paper and primarily due to the mismatching of different stages. It is of great importance to control the tip clearance. When tip clearance increases, the front stage tends to work near surge condition and the rear stage tends to work near choke condition, which leads to lower efficiency than in the middle stages. A weight was defined to evaluate each stage’s contribution to the whole compressor’s efficiency deficit caused by the increase of tip clearance. Front and rear stages contribute more to the efficiency deficit than the middle stages, which indicates that more attention should be paid on front and rear stages to improve the performance of multistage Axial Compressors. In order to evaluate the matching of multistage Axial Compressors with a quantified method, a new parameter named “Peak Efficiency Deviation (PED)” was defined based on the difference between each stage’s operating efficiency and its peak efficiency. The mass flow of multistage Axial Compressors should be well considered to make the PED parameter to be close to zero as possible. In the most commonly used range of tip clearance from 0.5% to 3.0% span, the PED varies little within 0.4 percent, which is only about 8.4% of the peak efficiency deficit at 1.5% span tip clearance. So, the PED could be small within a wide range of tip clearances if the matching of the compressor is perfect at design tip clearance.
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Influence of different loads on the stresses of multistage Axial compressor rotors
Proceedings of the Institution of Mechanical Engineers Part G: Journal of Aerospace Engineering, 2016Co-Authors: Xinqian Zheng, Chuang Ding, Yangjun ZhangAbstract:Multistage Axial Compressors are widely used in the gas turbine engines. The strength of rotors is one of the key factors for the reliability of multistage Axial Compressors. The stresses of rotors at real working conditions can be caused by the centrifugal load, thermal load, and aerodynamic load. It is important to figure out the roles and the mechanism of the three kinds of loads in the stresses generating process. In this paper, the stresses of rotors in a typical five-stage Axial compressor are calculated with different kinds of loads by solid–fluid coupling method. The results show that the proportion of the stress caused by centrifugal load is more than 80% of the total stress, which is dominant. The maximum proportion of the stress caused by thermal load is about 20% of the total stress at the front stages. However, the influence of thermal load is quite different from the first stage to the last stage. It is surprising that thermal load can decrease the stresses of the last stage rotor, which is ...
