摘要 :
The tandem airfoil has potential to do more work as a compressor blade than a single airfoil without incurring significantly higher losses. Although tandem blades are sometimes employed as stators, they have not been used in any k...
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The tandem airfoil has potential to do more work as a compressor blade than a single airfoil without incurring significantly higher losses. Although tandem blades are sometimes employed as stators, they have not been used in any known commercial rotors. While the long-term goal for this program is development of a commercially viable tandem rotor, this paper discusses tandem airfoils in subsonic, shock-free rectilinear cascade flow. Existing literature data on tandem airfoils in rectilinear cascades have been compiled and presented in a Lieblein loss versus loading correlation. Large scatter in the data gave motivation to conduct an extensive 2D computational fluid dynamics (CFD) study evaluating the overall performance as a function of the relative positions of the forward and aft airfoils. CFD results were consistent with trends in the open literature, both of which indicate that a properly designed tandem airfoil can outperform a comparable single airfoil on and off design. The general agreement of the CFD and literature data serves as a validation for the computational approach.
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In the present work the numerical simulation of a rectilinear blade cascade with surface roughness up to 100 μm over different locations of the turbine blade has been performed. It is observed that the effect of roughness on the ...
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In the present work the numerical simulation of a rectilinear blade cascade with surface roughness up to 100 μm over different locations of the turbine blade has been performed. It is observed that the effect of roughness on the efficiency of the turbine blade is more on the suction surface than that on the pressure surface. In case of suction surface, mass-averaged profile losses are more when roughness is provided on the trailing edge than on middle chord and losses are least when the roughness is provided on the leading edge, however pattern of losses is opposite with roughness on pressure surface.
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The unsteady aerodynamic characteristics of cascaded turbine blades oscillating in transonic flows were experimentally studied in a linear cascade tunnel by the influence coefficient method. Two flow patterns were adopted, one of ...
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The unsteady aerodynamic characteristics of cascaded turbine blades oscillating in transonic flows were experimentally studied in a linear cascade tunnel by the influence coefficient method. Two flow patterns were adopted, one of which had anear-design condition, and the other had an off-design condition with lower pressure ratio. From the measurement of unsteady aerodynamic force, a range of interblade phase angle was found where the blade vibration was unstable. The instability wasremarkable in the near-design point, while it was much suppressed in the off-design condition. It was realized that the negative influence coefficients of damping from neighboring blades of the oscillating one were added each other in the near-designcondition. In the off-design case, on the other hand, the coefficients were cancelled out to alleviate the instability. The different behavior of the damping should be attributable to the significant phase change of the aerodynamic force around shockimpingement point.
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The goal of the paper is to describe wake parameters of wakes from turbine cascades in compressible flows especially in planes where the leading edge of the following blade row would be located. Data from experiments with turbine ...
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The goal of the paper is to describe wake parameters of wakes from turbine cascades in compressible flows especially in planes where the leading edge of the following blade row would be located. Data from experiments with turbine cascades in compressible flow will be used to derive a theoretical approach which describes the wake growth and the recovery of the velocity deficit. The theory is based on similarity assumptions. The derived equations depend on simple and readily available parameters such as overall losses, exit angle, and Mach or Laval number. In compressible turbine flows, the influence of the inviscid flow field is of great importance. In this paper, an approach to take this influence into account when determining the behavior of the wake is presented. Correlations for basic characteristics of wakes in compressible flows are not readily available. Such correlations are necessary as input to unsteady flow and heat transfer calculation procedures for turbomachine blades. Based on available data on wake behavior in the compressible flow behind turbine blades, the correlations presented describe the wake behavior from the trailing edge to the confluence of the wakes of adjacent blades.
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Film-cooling effectiveness from shaped holes on the near tip pressure side and cylindrical holes on the squealer cavity floor is investigated. The pressure side squealer rim wall is cut near the trailing edge to allow the accumula...
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Film-cooling effectiveness from shaped holes on the near tip pressure side and cylindrical holes on the squealer cavity floor is investigated. The pressure side squealer rim wall is cut near the trailing edge to allow the accumulated coolant in the cavity to escape and cool the tip trailing edge. Effects of varying blowing ratios and squealer cavity depth are also examined on film-cooling effectiveness. The film-cooling effectiveness distributions are measured on the blade tip, near tip pressure side and the inner pressure side and suction side rim walls using pressure sensitive paint technique. The internal coolant-supply passages of the squealer tipped blade are modeled similar to those in the GE-E~3 rotor blade with two separate serpentine loops supplying coolant to the film-cooling holes. Two rows of cylindrical film-cooling holes are arranged offset to the suction side profile and along the camber line on the tip. Another row of shaped film-cooling holes is arranged along the pressure side just below the tip. The average blowing ratio of the cooling gas is controlled to be 0.5, 1.0, 1.5, and 2.0. A five-bladed linear cascade in a blow down facility with a tip gap clearance of 1.5% is used to perform the experiments. The free-stream Reynolds number, based on the axial chord length and the exit velocity, was 1,480,000 and the inlet and exit Mach numbers were 0.23 and 0.65, respectively. A blowing ratio of 1.0 is found to give best results on the pressure side, whereas the tip surfaces forming the squealer cavity give best results for M=2. Results show high film-cooling effectiveness magnitudes near the trailing edge of the blade tip due to coolant accumulation from upstream holes in the tip cavity. A squealer depth with a recess of 2.1 mm causes the average effectiveness magnitudes to decrease slightly as compared to a squealer depth of 4.2 mm.
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The unsteady flow field around an oscillating blade of a transonic turbine cascade was numerically analyzed with a developed Euler code. The aim was to clarify the mechanism of vibration instability of the turbine blades found in ...
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The unsteady flow field around an oscillating blade of a transonic turbine cascade was numerically analyzed with a developed Euler code. The aim was to clarify the mechanism of vibration instability of the turbine blades found in the previousexperiment. The numerical results were verified to well reproduce the unsteady flow fields obtained in the experiment in a qualitative sense. The vibration instability was found to come from the strong unsteady aerodynamic force in the midchord area of ablade, which was generated by the change of flow channel area due to the blade oscillation. When the shock wave from the adjacent blade impinged around the midchord position in an off-design flow condition, the phase angle of the unsteady forcesignificantly changed between the upstream and the downstream region of the shock. The vibration instability was thereby suppressed. When the oscillation frequency increased, the vibration was observed to become stable.
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For the first time, a systematic experimental investigation on flow fields and losses of an ultra-highly loaded turbine cascade with bowed blades has been conducted. Flow patterns, secondary flow vortices and vectors, losses, and ...
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For the first time, a systematic experimental investigation on flow fields and losses of an ultra-highly loaded turbine cascade with bowed blades has been conducted. Flow patterns, secondary flow vortices and vectors, losses, and yaw angles at the downstream outlet have been analysed based on the measurements. The results show that the flow fields downstream of the cascade are characterized by a complicated vortex structure including passage vortices (PVs), trailing edge vortices (TVs), and corner vortices (CVs). The high-loss cores at the cascade outlet roughly correspond to the high-vorticity regions. A−20° bow angle gives the optimal aerodynamic performance under the conditions of this work, but the overall improvement is not significant. Appropriate negative blade bowing weakens the PVs and TVs and prevents the meeting and mixing of the PVs at the midspan, hence improving the flow fields and reducing the overall losses. However, negative blade bowing also increases the flow separation in corner regions, and enhances the CVs and the accumulation of low-energy air flow. This partially counteracts the beneficial effects, making the overall improvement not significant. The pitch-averaged yaw angle at the outlet of the cascade varies dramatically over the whole span. Negative blade bowing can improve the uniformity of the yaw angle distribution at the outlet. On the contrary, positive blade bowing degrades the aerodynamic performance of the cascade.
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摘要 :
For the first time, a systematic experimental investigation on flow fields and losses of an ultra-highly loaded turbine cascade with bowed blades has been conducted. Flow patterns, secondary flow vortices and vectors, losses, and ...
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For the first time, a systematic experimental investigation on flow fields and losses of an ultra-highly loaded turbine cascade with bowed blades has been conducted. Flow patterns, secondary flow vortices and vectors, losses, and yaw angles at the downstream outlet have been analysed based on the measurements. The results show that the flow fields downstream of the cascade are characterized by a complicated vortex structure including passage vortices (PVs), trailing edge vortices (TVs), and corner vortices (CVs). The high-loss cores at the cascade outlet roughly correspond to the high-vorticity regions. A -20° bow angle gives the optimal aerodynamic performance under the conditions of this work, but the overall improvement is not significant. Appropriate negative blade bowing weakens the PVs and TVs and prevents the meeting and mixing of the PVs at the midspan, hence improving the flow fields and reducing the overall losses. However, negative blade bowing also increases the flow separation in corner regions, and enhances the CVs and the accumulation of low-energy air flow. This partially counteracts the beneficial effects, making the overall improvement not significant. The pitch-averaged yaw angle at the outlet of the cascade varies dramatically over the whole span. Negative blade bowing can improve the uniformity of the yaw angle distribution at the outlet. On the contrary, positive blade bowing degrades the aerodynamic performance of the cascade.
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Tip geometry modification is frequently used to suppress the tip leakage flow in the turbine cascade however a universally beneficial tip geometry modification design has not been fully discovered. In this paper, the two-surface c...
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Tip geometry modification is frequently used to suppress the tip leakage flow in the turbine cascade however a universally beneficial tip geometry modification design has not been fully discovered. In this paper, the two-surface coupling arbitrary blade tip design method in three-dimensional physical space which satisfies the simple trigonometric function law is proposed and the mathematical parametric description is presented. The effects of different arbitrary blade tips on tip leakage flow have been studied numerically in a highly loaded axial turbine cascade. The aerodynamic performance of different tips is assessed by the tip leakage mass flow rate and the total pressure loss coefficient at the exit section. The Kriging model and genetic optimization algorithm are used to optimize the arbitrary blade tips to obtain the optimal arbitrary blade tip. Compared with the flat tip, the tip leakage mass flow rate is decreased by 10.57% and the area-average total pressure loss coefficient at the exit section is reduced by 8.91% in the optimal arbitrary blade tip.
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The throat area is a geometric parameter of the blade ring necessary to profile its blades and compute the turbine capacity. As applied to the filament flow model, the area is defined by the involute of the throat solid figure ont...
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The throat area is a geometric parameter of the blade ring necessary to profile its blades and compute the turbine capacity. As applied to the filament flow model, the area is defined by the involute of the throat solid figure ontothe plane formed by the cascade throat located on one of the cylindrical sections of the blade ring and the radius. An equation is derived for computing the area of the involute, which considers the effect of the shape of the ring's tailing outlines and the fillets at the transition from the outlines to the blade feather. Comparison of the area values for several turbines computed by the derived equation and by a more complex method based on a search for the minimum distances from the tailing edge of the blade to the suction surface of the neighboring blade in the channel revealed slight differences. The fluid-dynamic 2D analysis determined the radial boundaries of the filament bands, the parameters of the cascade that lie on a filament's cylindrical surfaces, and the flow velocity normal to the throat section of the filament. The proposed approach to computation of the throat area is common for problems of both designing and analyzing the turbine operation and allows for excluding, in practice, methodological differences in determination of the flow rate and the flow angles at the outlet of the blade ring.
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