Effect of Active Modulation of Through-Casing Coolant Injection on Turbine Efficiency

2017 ◽  
Author(s):  
Brian M. T. Tang ◽  
Marko Bacic ◽  
Peter T. Ireland
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Total Pressure ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Turbine Efficiency ◽  
Coolant Injection ◽  
Cooling Air

This paper presents a computational investigation into the impact of cooling air injected through the stationary over-tip turbine casing on overall turbine efficiency. The high work axial flow turbine is representative of the high pressure turbine of a civil aviation turbofan engine. The effect of active modulation of the cooling air is assessed, as well as that of the injection locations. The influence of the through-casing coolant injection on the turbine blade over-tip leakage flow and the associated secondary flow features are examined. Transient (unsteady) sliding mesh simulations of a one turbine stage rotor-stator domain are performed using periodic boundary conditions. Cooling air configurations with a constant total pressure air supply, constant mass flow rate and actively controlled total pressure supply are assessed for a single geometric arrangement of cooling holes. The effects of both the mass flow rate of cooling air and the location of its injection relative to the turbine rotor blade are examined. The results show that all of the assessed cooling configurations provided a benefit to turbine row efficiency of between 0.2 and 0.4 percentage points. The passive and constant mass flow rate configurations reduced the over-tip leakage flow, but did so in an inefficient manner, with decreasing efficiency observed with increasing injection mass flow rate beyond 0.6% of the mainstream flow, despite the over-tip leakage mass flow rate continuing to reduce. By contrast, the active total pressure controlled injection provided a more efficient manner of controlling this leakage flow, as it permitted a redistribution of cooling air, allowing it to be applied in the regions close to the suction side of the blade tip which more directly reduced over-tip leakage flow rates and hence improved efficiency. Cooling air injected close to the pressure side of the rotor blade was less effective at controlling the leakage flow, and was associated with increased aerodynamic loss in the passage vortex.

Stall Inception and Development Process Due to Tip Leakage Flow in Axial Compressor Rotor Blades Row

2014 ◽  
Vol 30 (3) ◽  
pp. 307-313 ◽  
Author(s):  
R. Taghavi-Zenou ◽  
S. Abbasi ◽  
S. Eslami
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Axial Compressor ◽  
Leading Edge ◽  
Rotor Blades ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Compressor Rotor

ABSTRACTThis paper deals with tip leakage flow structure in subsonic axial compressor rotor blades row under different operating conditions. Analyses are based on flow simulation utilizing computational fluid dynamic technique. Three different circumstances at near stall condition are considered in this respect. Tip leakage flow frequency spectrum was studied through surveying instantaneous static pressure signals imposed on blades surfaces. Results at the highest flow rate, close to the stall condition, showed that the tip vortex flow fluctuates with a frequency close to the blade passing frequency. In addition, pressure signals remained unchanged with time. Moreover, equal pressure fluctuations at different passages guaranteed no peripheral disturbances. Tip leakage flow frequency decreased with reduction of the mass flow rate and its structure was changing with time. Spillage of the tip leakage flow from the blade leading edge occurred without any backflow in the trailing edge region. Consequently, various flow structures were observed within every passage between two adjacent blades. Further decrease in the mass flow rate provided conditions where the spilled flow ahead of the blade leading edge together with trailing edge backflow caused spike stall to occur. This latter phenomenon was accompanied by lower frequencies and higher amplitudes of the pressure signals. Further revolution of the rotor blade row caused the spike stall to eventuate to larger stall cells, which may be led to fully developed rotating stall.

Effect of the Double-Slot Injection on the Leakage Flow Control in a Honeycomb-Tip Turbine Cascade

2019 ◽  
Author(s):  
Yabo Wang ◽  
Yanping Song ◽  
Jianyang Yu ◽  
Fu Chen
Keyword(s):  
Flow Control ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Pressure Loss ◽  
Total Pressure ◽  
Total Pressure Loss ◽  
Leakage Flow ◽  
Turbine Cascade ◽  
Tip Leakage

Abstract The effect of five arrangements of the double-slot injections on the leakage flow control is studied in a honeycomb-tip turbine cascade numerically. The honeycomb tip is covered with 67 intact honeycomb cavities, since the uneven tip is wearable and the cavity vortex could realize the aerodynamic sealing for the leakage flow. Then in the present study, a pair of injection slots is arranged blow each cavity, aiming to enhance the leakage flow suppression by modifying the cavity vortex. According to the orientation of the two slots, five designs of the double-slot injections are proposed. In detail, the two slots are opposite to each other or keep tangential to the original cavity vortex roughly. The three dimensional calculations were completed by using Reynolds-averaged Navier-Stokes (RANS) method and the k-ω turbulence model in the commercial software ANSYS CFX. The estimation of these tip designs is mainly according to the tip leakage mass flow rate and the total pressure loss. Firstly, the injection structures induced by the slots can be divided into X- and T-types inside the cavity. The results show that the T-type structure is more effective in reducing the tip leakage mass flow rate, with the maximum reduction up to 48.2%. Then the effect on the flow field inside the gap and the secondary flow in the upper passage is analyzed. Compared with the flat tip, the span-wise position of the tip leakage vortex core drops within the cascade and the range of the affected loss region expands. At the cascade exit, the tip leakage vortex moves toward the passage vortex near the casing, while the latter’s core rises. The position changes of the secondary vortices eventually determine the total pressure loss contour downstream the cascade. Finally, the injection total pressure and the upper casing motion are investigated. Interestingly, the injection intensity (mass flow rate) increases with the injection total pressure but this value decreases as the casing speed increases. The tip leakage mass flow rate decreases linearly as increasing the injection total pressure or the casing speed. Yet the averaged total pressure loss downstream the cascade increases with the injection total pressure but appears a nonlinear distribution against the casing speed.

Axial Turbine Tip Desensitization by Injection From a Tip Trench: Part 1 — Effect of Injection Mass Flow Rate

2004 ◽  
Author(s):  
Nikhil M. Rao ◽  
Cengiz Camci
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Total Pressure ◽  
Large Scale ◽  
Dynamic Pressure ◽  
Coolant Injection ◽  
Gap Height ◽  
Tip Desensitization ◽  
Injection Rates

An experimental study of a turbine tip desensitization method based on tip coolant injection was conducted in a large-scale rotating turbine rig. One of twenty-nine rotor blades was modified and instrumented to have a tip trench with discrete injection holes directed towards the pressure side. Time accurate absolute total pressure was measured 0.3 chord lengths downstream of the rotor exit plane using a fast response dynamic pressure sensor in a phase-locked manner. The test cases presented include results for tip gap heights of 1.40% and 0.72% of the blade height, and coolant injection rates of 0.41%, 0.52%, 0.63%, and 0.72% core mass flow rate. At a gap height of 1.40% the leakage vortex is large, occupying about 15% blade span. A reduction in gap height causes the leakage vortex to reduce in size and move towards the blade suction side. The minimum total pressure measured, for the reduced gap, in the leakage vortex is about 4% greater. Coolant injection from the tip trench is successful in filling in the total pressure defect originally resulting from the leakage vortex without injection. At the higher tip injection rates the leakage vortex is also seen to have moved towards the blade tip. The high momentum associated with the tip jets affects the total pressure distributions in the neighboring passages.

The Effect of the Degree of Reaction on the Leakage Loss in Steam Turbines

2013 ◽  
Vol 135 (2) ◽  
Author(s):  
Sungho Yoon
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Leakage Flow ◽  
Steam Turbines ◽  
Efficiency Loss ◽  
Tip Leakage ◽  
Leakage Flows ◽  
Rotating Blade ◽  
Degree Of Reaction

The degree of reaction selected in designing steam turbines is of paramount importance. There has been competition between 50% reaction and impulse turbines over a century. It is, therefore, important to understand the effect of the degree of reaction on aerodynamic performance. In particular, a change in the degree of reaction affects the leakage flow substantially in both the stationary and rotating blades due to a change in the blade loading. The effect of the degree of reaction on the efficiency loss due to leakage flows is systematically investigated in this paper using analytical models. It is shown that the appropriate way to understand the efficiency loss due to leakage flows is to estimate the kinetic energy dissipation rather than the leakage mass flow rate, as demonstrated by Yoon et al. (Yoon, S., Curtis, E., Denton, J., and Longley, J., 2010, “The Effect of Clearance on Shrouded and Unshrouded Turbine at Two Different Levels of Reaction,” ASME Paper No. GT2010-22541). In order to estimate the efficiency loss due to leakage flows, the well-known Denton model (Denton, J. D., 1993, “Loss Mechanisms in Turbomachinery,” ASME J. Turbomach., 115, pp. 621–656) is extended by considering the velocity triangles in a repeating turbine stage. The extended model is compared with experimental data, at different degrees of reaction, and shows good agreement with measurements. It is shown that a reduction in the degree of reaction, at a fixed flow coefficient and a fixed work coefficient, results in an increase in the efficiency loss across the stationary blade but a decrease in that across the rotating blade. However, the efficiency loss across the stationary blade hub is estimated to be smaller than the efficiency loss across the rotating blade tip. A stationary blade can be better sealed than a rotating blade by applying multiple seals and using a leakage path with a low radius. The efficiency loss due to the tip leakage flow is substantially influenced by the choice of the tip configuration. Shrouded blades show several aerodynamic advantages over unshrouded blades in reducing the tip leakage efficiency loss. Employing multiple seals over the shroud decreases the tip leakage mass flow rate significantly. Moreover, as the degree of reaction approaches zero, the tip leakage mass flow rate over the shroud becomes small since the axial pressure drop across the rotating blade becomes small. In unshrouded blades, a reduction in the degree of reaction is shown to increase the leakage mass flow rate over the tip because the circumferential pressure difference between the blade pressure side and blade suction side generally increases when the pitch-to-chord ratio remains unchanged.

Effect of arbitrary blade tip design on tip leakage flow

2019 ◽  
Vol 234 (1) ◽  
pp. 19-30
Author(s):  
Jiahui Jin ◽  
Yanping Song ◽  
Jianyang Yu ◽  
Fu Chen
Keyword(s):  
Flow Rate ◽  
Total Pressure ◽  
Leakage Flow ◽  
Exit Section ◽  
Turbine Cascade ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Pressure Loss Coefficient ◽  
Blade Tip ◽  
Total Pressure Loss Coefficient

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.

Numerical and Experimental Investigation of Aerodynamic Performance for a Straight Turbine Cascade With a Novel Partial Shroud

2015 ◽  
Vol 138 (3) ◽  
Author(s):  
Yan Liu ◽  
Tian-Long Zhang ◽  
Min Zhang ◽  
Meng-Chao Zhang
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Cross Sections ◽  
Total Pressure ◽  
Pressure Coefficient ◽  
Aerodynamic Performance ◽  
Turbine Cascade ◽  
Tip Leakage ◽  
Partial Shroud

A comparative experimental and numerical analysis is carried out to assess the aerodynamic performance of a novel partial shroud in a straight turbine cascade. This partial shroud is designed as a combination of winglet and shroud. A plain tip is employed as a baseline case. A pure winglet tip is also studied for comparison. Both experiments and predictions demonstrate that this novel partial shroud configuration has aerodynamic advantages over the pure winglet arrangement. Predicted results show that, relative to the baseline blade with a plain tip, using the partial shroud can lead to a reduction of 20.89% in the mass-averaged total pressure coefficient on the upper half-span of a plane downstream of the cascade trailing edge and 16.53% in the tip leakage mass flow rate, whereas the pure winglet only decreases these two performance parameters by 11.36% and 1.32%, respectively. The flow physics is explored in detail to explain these results via topological analyses. The use of this new partial shroud significantly affects the topological structures and total pressure loss coefficients on various axial cross sections, particularly at the rear part of the blade passage. The partial shroud not only weakens the tip leakage vortex (TLV) but also reduces the strength of passage vortex near the casing (PVC) endwall. Furthermore, three partial shrouds with width-to-pitch ratios of 3%, 5%, and 7% are considered. With an increase in the width of the winglet part, improvements in aerodynamics and the tip leakage mass flow rate are limited.

Effect of the honeycomb tip with injection on the aerodynamic performance in a 1.5-stage turbine

2020 ◽  
pp. 1-25
Author(s):  
Jianyang Yu ◽  
Yabo Wang ◽  
YanPing Song ◽  
Fu Chen
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Pressure Loss ◽  
Total Pressure ◽  
Total Pressure Loss ◽  
Navier Stokes ◽  
Total Efficiency ◽  
Cavity Depth ◽  
Tip Leakage

Abstract Three kinds of rotor tip configurations have been investigated numerically in the LISA 1.5-stage turbine, including the flat tip, the honeycomb tip and the honeycomb tip with injection. The effect of the cavity depth and the injection mass flow rate on the turbine performance is studied in detail, evaluated by the isentropic total-to-total efficiency and the tip leakage mass flow rate. The Reynolds-averaged Navier-Stokes (RANS) method and the k-ω turbulence model are adopted in all the present computations. The numerical results show that the first stage efficiency is increased by up to 0.66% and the tip leakage mass flow rate is reduced by about 1.87% of the main flow. The pressure field and the flow feature inside the gap are explored. The flow structures and the total pressure loss contours in the rotor passage are presented. Finally, the total pressure loss is newly defined by considering the injection effect. It is indicated that the injection mass flow rate should be carefully determined for excellent overall performance.

Application of Casing Circumferential Grooves to Counteract the Influence of Tip Clearance

2008 ◽  
Author(s):  
Victor Mileshin ◽  
Igor Brailko ◽  
Andrew Startsev
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Pressure Ratio ◽  
Leading Edge ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Blade Height ◽  
Transonic Compressor

Widening of surge margin of a transonic compressor stage is the main objective of the paper. This stage is a typical middle stage of a modern high pressure compressor (HPC) with decreased number of stages. Hot tip clearance of the stage being integrated into a six-stage HPC providing total pressure ratio π* HPC ≥ 12 and mass flow-rate < 16 kg/sec is estimated at 2.5 – 3% of blade height and is classified as a large tip clearance. In this paper experimental and 3D viscous numerical performances of the stage are obtained for two values of rotor tip clearance — equal to 0.76% (small size) and 2.66% (large size) of blade height. In doing so, tip clearance enlargement from 0.76% to 2.66% has been made by increase of casing (shroud) radius. This increase is manufactured as a circumferential trench (recess) with axial width 30% larger than rotor axial chord. Below this tip clearance is called “recessed” tip clearance. A distinguishing feature of leakage flow in case of large tip clearance is a formation of reversed flow near rotor casing. This backflow being intensified by throttling causes increase of incidence at the rotor leading edge and development of rotor stall. Casing treatments are intended to inhibit and delay the process. Among them circumferential grooves is the simplest casing treatment. Investigated in this paper casing circumferential grooves cover 82% of rotor axial chord. Numerical visualization of the near-casing streamlines demonstrates that tip leakage flow drains into the casing grooves giving rise to extended domains of positive axial velocity. Calculated mass flow-rate through groove’s cross-section demonstrates maximum over the rotor blade tip (flow into the groove) and minimum at mid-pitch (flow out of the groove). Amplitude of this variation depends on the groove location and stage throttling.

The Effect of the Degree of Reaction on the Leakage Loss in Steam Turbines

2012 ◽  
Author(s):  
Sungho Yoon
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Leakage Flow ◽  
Steam Turbines ◽  
Efficiency Loss ◽  
Tip Leakage ◽  
Leakage Flows ◽  
Rotating Blade ◽  
Degree Of Reaction

The degree of reaction selected in designing steam turbines is of paramount importance. There has been competition between 50% reaction and impulse turbines over a century. It is therefore important to understand the effect of the degree of reaction on aerodynamic performance. In particular, a change in the degree of reaction affects the leakage flow substantially in both the stationary and rotating blades due to a change in the blade loading. The effect of the degree of reaction on the efficiency loss, due to leakage flows, is systematically investigated in this paper using analytical models. It is shown that the appropriate way to understand the efficiency loss, due to leakage flows, is to estimate the kinetic energy dissipation rather than the leakage mass flow rate, as demonstrated by Yoon et al. [1]. In order to estimate the efficiency loss due to leakage flows, the well-known Denton model [2] is extended by considering the velocity triangles in a repeating turbine stage. The extended model is compared with experimental data, at different degrees of reaction, and shows good agreement with measurements. It is shown that a reduction in the degree of reaction, at a fixed flow coefficient and a fixed work coefficient, results in an increase in the efficiency loss across the stationary blade, but a decrease in that across the rotating blade. However, the efficiency loss, across the stationary blade hub, is estimated to be smaller than the efficiency loss across the rotating blade tip. A stationary blade can be better sealed than a rotating blade by applying multiple seals and using a leakage path with a low radius. The efficiency loss, due to the tip leakage flow, is substantially influenced by the choice of the tip configuration. Shrouded blades show several aerodynamic advantages over unshrouded blades in reducing the tip leakage efficiency loss. Employing multiple seals over the shroud decreases the tip leakage mass flow rate significantly. Moreover, as the degree of reaction approaches zero, the tip leakage mass flow rate over the shroud becomes small, since the axial pressure drop across the rotating blade becomes small. In unshrouded blades, a reduction in the degree of reaction is shown to increase the leakage mass flow rate over the tip, because the circumferential pressure difference between the blade pressure side and blade suction side generally increases when the pitch-to-chord ratio remains unchanged.

Impact of Passive Tip-Injection on the Performance of Partially Shrouded Turbines: Basic Concept and Preliminary Results

2013 ◽  
Author(s):  
Pouya Ghaffari ◽  
Reinhard Willinger
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Gas Turbines ◽  
Turbine Blades ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Blade Tip ◽  
Tip Injection ◽  
The Impact

In terms of efficiency improvement many methods for reducing the blade tip-leakage mass flow rate have been proposed. Some of these methods are based on increasing the flow resistance with aid of geometrical modifications of the blade tip (squealers, winglets, shrouded blades, etc.) whereas other methods take advantage of aerodynamical resistance with passive tip-injection as an example. The objective of this paper is a combination of both methods in order to achieve higher reduction in tip-leakage mass flow rate. In the first part of this work necessary characteristic parameters of modern low pressure turbine blades in aircraft gas turbines are estimated. These parameters are taken into consideration to calculate the range of physical quantities influencing tip-leakage flow. Subsequently a two dimensional flow model is obtained with the so called discharge coefficient as the ratio of the actual tip gap mass flow rate to its highest possible value. The investigations are based on dimensionless calculations. In the end the results obtained from dimensionless 2D CFD-simulations are presented and compared with the analytical results. This leads to conclusions regarding the impact of various parameters on the effectiveness of the passive tip-injection.

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