Journal articles on the topic 'Tip clearance measurements in turbomachines'
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1
Kameier, F., and W. Neise. "Experimental Study of Tip Clearance Losses and Noise in Axial Turbomachines and Their Reduction." Journal of Turbomachinery 119, no. 3 (July 1, 1997): 460–71. http://dx.doi.org/10.1115/1.2841145.
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An experimental study is described to investigate the negative effects of the tip clearance gap on the aerodynamic and acoustic performance of axial turbomachines. In addition to the increased broadband levels reported in the literature when the tip clearance is enlarged, significant level increases were observed within narrow frequency bands below the blade passing frequency. Measurements of the pressure and velocity fluctuations in the vicinity of the blade tips reveal that the tip clearance noise is associated with a rotating flow instability at the blade tip, which in turn is only present under reversed flow conditions in the tip clearance gap. A turbulence generator inserted into the tip clearance gap is found to be effective in eliminating the tip clearance noise and in improving the aerodynamic performance.
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Jia, Bing Hui, and Xiao Dong Zhang. "Study on Effect of Rotor Vibration on Tip Clearance Variation and Fast Active Control of Tip Clearance." Advanced Materials Research 139-141 (October 2010): 2469–72. http://dx.doi.org/10.4028/www.scientific.net/amr.139-141.2469.
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The tip clearance flow of axial turbomachines is important for their aerodynamic and maneuver performance. And the tip clearance gap leakage flow is of continuing concern in reducing efficiency losses that occur within turbines. In order to gain significant reductions in emissions and specific fuel consumption as well as dramatic improvements in operating efficiency and increased service life of aero-engine, variation mechanism of blade tip clearance was analyzed and the equation of dynamic clearance was shown firstly, then the effect of rotor vibration in clearance variation which include flight loads and engine loads was studied in this paper; based on the dynamic measurements of blade tip clearance, a method that ensure tip clearance at optimal state in given mission profile through active rotor vibration control and active tip clearance control was presented. Besides, fuzzy control theory was used to solve the high nonlinear variation of tip clearance. The analysis result shows that this technique is useful.
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Dambach, R., H. P. Hodson, and I. Huntsman. "1998 Turbomachinery Committee Best Paper Award: An Experimental Study of Tip Clearance Flow in a Radial Inflow Turbine." Journal of Turbomachinery 121, no. 4 (October 1, 1999): 644–50. http://dx.doi.org/10.1115/1.2836716.
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This paper describes an experimental investigation of tip clearance flow in a radial inflow turbine. Flow visualization and static pressure measurements were performed. These were combined with hot-wire traverses into the tip gap. The experimental data indicate that the tip clearance flow in a radial turbine can be divided into three regions. The first region is located at the rotor inlet, where the influence of relative casing motion dominates the flow over the tip. The second region is located toward midchord, where the effect of relative casing motion is weakened. Finally, a third region exists in the exducer, where the effect of relative casing motion becomes small and the leakage flow resembles the tip flow behavior in an axial turbine. Integration of the velocity profiles showed that there is little tip leakage in the first part of the rotor because of the effect of scraping. It was found that the bulk of tip leakage flow in a radial turbine passes through the exducer. The mass flow rate, measured at four chordwise positions, was compared with a standard axial turbine tip leakage model. The result revealed the need for a model suited to radial turbines. The hot-wire measurements also indicated a higher tip gap loss in the exducer of the radial turbine. This explains why the stage efficiency of a radial inflow turbine is more affected by increasing the radial clearance than by increasing the axial clearance.
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Schrapp, H., U. Stark, and H. Saathoff. "Unsteady behaviour of the tip clearance vortex in a rotor equivalent compressor cascade." Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy 223, no. 6 (July 6, 2009): 635–43. http://dx.doi.org/10.1243/09576509jpe816.
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From earlier experimental investigations in a single-stage axial-flow pump and different numerical calculations of the flow in single-stage axial-flow compressors, it is known that vortex breakdown of the tip clearance vortex can take place in turbomachines, although an experimental proof for subsonic compressors is lacking. Vortex breakdown, if existent, is a source of high instability in the sensitive tip region of axial-flow pumps and compressors and will also play an important role in the stall inception process. Therefore, the flow in a linear compressor cascade with a 3 per cent tip clearance to one side has been investigated at different flow angles from the design point up to the stability limit of the cascade. The cascade resembles the tip section of a single-stage, axial-flow, low-speed compressor that is also in use at the Technical University of Braunschweig. The measuring techniques used were (a) a commercial particle image velocimetry (PIV) system and (b) a pressure measuring system with several flush mounted high-response pressure transducers at selected locations where the vortex was expected. As the cascade approaches its stall limit, the analysis of the pressure signals in the frequency domain revealed a bump of increased amplitude at a certain non-dimensional frequency for some of the measuring positions. The measuring positions that exhibited the bump correlated very well with a paraboloid-shaped region of high standard deviation enveloping an area of very low momentum fluid. It is shown that the frequency of the striking bump corresponds to the rotational frequency of the vortex calculated from the PIV measurements.
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Van Zante, Dale E., Anthony J. Strazisar, Jerry R. Wood, Michael D. Hathaway, and Theodore H. Okiishi. "Recommendations for Achieving Accurate Numerical Simulation of Tip Clearance Flows in Transonic Compressor Rotors." Journal of Turbomachinery 122, no. 4 (February 1, 1999): 733–42. http://dx.doi.org/10.1115/1.1314609.
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The tip clearance flows of transonic compressor rotors are important because they have a significant impact on rotor and stage performance. A wall-bounded shear layer formed by the relative motion between the overtip leakage flow and the shroud wall is found to have a major influence on the development of the tip clearance flow field. This shear layer, which has not been recognized by earlier investigators, impacts the stable operating range of the rotor. Simulation accuracy is dependent on the ability of the numerical code to resolve this layer. While numerical simulations of these flows are quite sophisticated, they are seldom verified through rigorous comparisons of numerical and measured data because these kinds of measurements are rare in the detail necessary to be useful in high-speed machines. In this paper we compare measured tip-clearance flow details (e.g., trajectory and radial extent) with corresponding data obtained from a numerical simulation. Laser-Doppler Velocimeter (LDV) measurements acquired in a transonic compressor rotor, NASA Rotor 35, are used. The tip clearance flow field of this transonic rotor is simulated using a Navier–Stokes turbomachinery solver that incorporates an advanced k–ε turbulence model derived for flows that are not in local equilibrium. A simple method is presented for determining when the wall-bounded shear layer is an important component of the tip clearance flow field. [S0889-504X(00)02504-6]
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Kunz, R. F., B. Lakshminarayana, and A. H. Basson. "Investigation of Tip Clearance Phenomena in an Axial Compressor Cascade Using Euler and Navier–Stokes Procedures." Journal of Turbomachinery 115, no. 3 (July 1, 1993): 453–67. http://dx.doi.org/10.1115/1.2929274.
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Three-dimensional Euler and full Navier–Stokes computational procedures have been utilized to simulate the flow field in an axial compressor cascade with tip clearance. An embedded H-grid topology was utilized to resolve the flow physics in the tip gap region. The numerical procedure employed is a finite difference Runge-Kutta scheme. Available measurements of blade static pressure distributions along the blade span, dynamic pressure and flow angle in the cascade outlet region, and spanwise distributions of blade normal force coefficient and circumferentially averaged flow angle are used for comparison. Several parameters that were varied in the experimental investigations were also varied in the computational studies. Specifically, measurements were taken and computations were performed on the configuration with and without: tip clearance, the presence of an endwall, inlet endwall total pressure profiles and simulated relative casing rotation. Additionally, both Euler and Navier–Stokes computations were performed to investigate the relative performance of these approaches in reconciling the physical phenomena considered. Results indicate that the Navier–Stokes procedure, which utilizes a low Reynolds number k–ε model, captures a variety of important physical phenomena associated with tip clearance flows with good accuracy. These include tip vortex strength and trajectory, blade loading near the tip, the interaction of the tip clearance flow with passage secondary flow, and the effects of relative endwall motion. The Euler computation provides good but somewhat diminished accuracy in resolution of some of these clearance phenomena. It is concluded that the level of modeling embodied in the present approach is sufficient to extract much of the tip region flow field information useful to designers of turbomachinery.
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Farrell, K. J., and M. L. Billet. "A Correlation of Leakage Vortex Cavitation in Axial-Flow Pumps." Journal of Fluids Engineering 116, no. 3 (September 1, 1994): 551–57. http://dx.doi.org/10.1115/1.2910312.
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Tip clearance flow in turbomachinery can lead to losses in efficiency and stall margin. In liquid handling turbomachinery, the vortical flow field, formed from the interaction of the leakage flow with the through-flow, is subject to cavitation. Furthermore, this flow field is complex and not well understood. A correlation of variables which predict the vortex minimum pressure has been formulated. Measurements of the important variables for this correlation have been made on a high Reynolds number (3 × 106) axial-flow test rig. The correlation has been applied to the measured data and other data sets from the literature with good agreement. An optimum tip clearance has been theoretically identified as experiments have shown. Observations of cavitation indicate a second vortex originating along the suction side trailing edge.
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Dawes, W. N. "A Numerical Analysis of the Three-Dimensional Viscous Flow in a Transonic Compressor Rotor and Comparison With Experiment." Journal of Turbomachinery 109, no. 1 (January 1, 1987): 83–90. http://dx.doi.org/10.1115/1.3262074.
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The numerical analysis of highly loaded transonic compressors continues to be of considerable interest. Although much progress has been made with inviscid analyses, viscous effects can be very significant, especially those associated with shock–boundary layer interactions. While inviscid analyses have been enhanced by the interactive inclusion of blade surf ace boundary layer calculations, it may be better in the long term to develop efficient algorithms to solve the full three-dimensional Navier–Stokes equations. Indeed, it seems that many phenomena of key interest, like tip clearance flows, may only be accessible to a Navier–Stokes solver. The present paper describes a computer program developed for solving the three-dimensional viscous compressible flow equations in turbomachine geometries. The code is applied to the study of the flowfield in an axial-flow transonic compressor rotor with an attempt to resolve the tip clearance flow. The predicted flow is compared with laser anemometry measurements and good agreement is found.
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Geng, Linlin, Desheng Zhang, Jian Chen, and Xavier Escaler. "Large-Eddy Simulation of Cavitating Tip Leakage Vortex Structures and Dynamics around a NACA0009 Hydrofoil." Journal of Marine Science and Engineering 9, no. 11 (October 30, 2021): 1198. http://dx.doi.org/10.3390/jmse9111198.
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The tip leakage vortex (TLV) has aroused great concern for turbomachine performance, stability and noise generation as well as cavitation erosion. To better understand structures and dynamics of the TLV, large-eddy simulation (LES) is coupled with a homogeneous cavitation model to simulate the cavitation flow around a NACA0009 hydrofoil with a given clearance. The numerical results are validated by comparisons with experimental measurements. The results demonstrate that the present LES can well predict the mean behavior of the TLV. By visualizing the mean streamlines and mean streamwise vorticity, it shows that the TLV dominates the end-wall vortex structures, and that the generation and evolution of the other vortices are found to be closely related to the development of the TLV. In addition, as the TLV moves downstream, it undergoes an interesting progression, i.e., the vortex core radius keeps increasing and the axial velocity of vortex center experiences a conversion from jet-like profile to wake-like profile.
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Vazquez Gonzalez, Adrián, Andrés Meana-Fernández, and Jesús Manuel Fernández. "Stator–rotor interaction in the tip leakage flow of an inlet vaned low-speed axial fan." International Journal of Numerical Methods for Heat & Fluid Flow 30, no. 10 (January 11, 2020): 4425–52. http://dx.doi.org/10.1108/hff-07-2019-0593.
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Purpose The purpose of the paper is to quantify the impact of the non-uniform flow generated by the upstream stator on the generation and convection of the tip leakage flow (TLF) structures in the passages of the rotor blades in a low-speed axial fan. Design/methodology/approach A full three dimensional (3D)-viscous unsteady Reynolds-averaged Navier-stokes (RANS) (URANS) simulation of the flow within a periodic domain of the axial stage has been performed at three different flow rate coefficients (φ = 0.38, 0.32, 0.27) using ReNormalization Group k-ε turbulence modelling. A typical tip clearance of 2.3 per cent of the blade span has been modelled on a reduced domain comprising a three-vaned stator and a two-bladed rotor with circumferential periodicity. A non-conformal grid with hybrid meshing, locally refined O-meshes on both blades and vanes walls with (100 × 25 × 80) elements, a 15-node meshed tip gap and circumferential interfaces for sliding mesh computations were also implemented. The unsteady motion of the rotor has been covered with 60 time steps per blade event. The simulations were validated with experimental measurements of the static pressure in the shroud of the blade tip region. Findings It has been observed that both TLF and intensities of the tip leakage vortex (TLV) are significantly influenced by upstream stator wakes, especially at nominal and partial load conditions. In particular, the leakage flow, which represents 12.4 per cent and 11.3 per cent of the working flow rate, respectively, has shown a clear periodic fluctuation clocked with the vane passing period in the relative domain. The periodic fluctuation of the TLF is in the range of 2.8-3.4 per cent of the mean value. In addition, the trajectory of the tip vortex is also notably perturbed, with root-mean squared fluctuations reaching up to 18 per cent and 6 per cent in the regions of maximum interaction at 50 per cent and 25 per cent of the blade chord for nominal and partial load conditions, respectively. On the contrary, the massive flow separation observed in the tip region of the blades for near-stall conditions prevents the formation of TLV structures and neglects any further interaction with the upstream vanes. Research limitations/implications Despite the increasing use of large eddy simulation modelling in turbomachinery environments, which requires extremely high computational costs, URANS modelling is still revealed as a useful technique to describe highly complex viscous mechanisms in 3D swirl flows, such as unsteady tip flow structures, with reasonable accuracy. Originality/value The paper presents a validated numerical model that simulates the unsteady response of the TLF to upstream perturbations in an axial fan stage. It also provides levels of instabilities in the TLV derived from the deterministic non-uniformities associated to the vane wakes.
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Dhadwal, H. S., and A. P. Kurkov. "Dual-Laser Probe Measurement of Blade-Tip Clearance." Journal of Turbomachinery 121, no. 3 (July 1, 1999): 481–85. http://dx.doi.org/10.1115/1.2841340.
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This paper describes two dual-laser probe integrated fiber optic systems for measuring blade tip clearance in rotating turbomachinery. The probes are nearly flush with the casing inner lining, resulting in minimal flow disturbance. The two probes are closely spaced in a circumferential plane and are slanted at an angle relative to each other so that the blade tip traverse time of the space between the two laser beams varies with the tip radius, allowing determination of the tip clearance at the rotor operating conditions. The tip clearance can be obtained for all the blades in a rotor with a single system, provided there are no synchronous vibrations present at a particular operating condition. These probes were installed in two holders; one provided an included angle between the probes of 20 deg, and the other provided an included angle of 40 deg. The two configurations were calibrated in a vacuum spin rig facility that is capable of reproducing realistic blade tip speeds.
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Khalid, S. A. "Factors Affecting Measured Axial Compressor Tip Clearance Vortex Circulation." Journal of Turbomachinery 117, no. 3 (July 1, 1995): 487–90. http://dx.doi.org/10.1115/1.2835685.
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The relationship between turbomachinery blade circulation and tip clearance vortex circulation measured experimentally is examined using three-dimensional viscous flow computations. It is shown that the clearance vortex circulation one would measure is dependent on the placement of the fluid contour around which the circulation measurement is taken. Radial transport of vorticity results in the magnitude of the measured clearance vortex circulation generally being less than the blade circulation. For compressors, radial transport of vorticity shed from the blade tip in proximity to the endwall is the principal contributor to the discrepancy between the measured vortex circulation and blade circulation. Further, diffusion of vorticity shed at the blade tip toward the endwall makes it impossible in most practical cases to construct a fluid contour around the vortex that encloses all, and only, the vorticity shed from the blade tip. One should thus not expect agreement between measured tip clearance vortex circulation and circulation around the blade.
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Shao, Ziyi, Wen Li, Yangli Zhu, Xing Wang, Xuehui Zhang, Haisheng Chen, and Wei Qin. "Tip leakage flow analysis of an axial turbine under the effect of separation at low Reynolds number." Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy 234, no. 6 (October 23, 2019): 751–65. http://dx.doi.org/10.1177/0957650919882877.
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The tip clearance flow could lead to work reduction and loss generation in turbomachines. However, the effect of separation at low Reynolds number on leakage flow is seldom studied. The previous method for evaluating tip leakage characteristics should also be further researched. Thus, numerical investigations on the tip clearance flow in an unshrouded axial-inflow turbine are conducted at low Reynolds number (3.5 × 104 of the rotor outlet at the designed condition) in the present study. The flow patterns and leakage mass flow rate of the clearance have been analyzed in detail. It is found that the tip clearance flow is greatly affected by the flow separation caused by low Reynolds number. The scraping ratio adopted in previous references does not accord with the clearance flow characteristics at low Reynolds number, especially in the front part of the clearance. A coefficient by −0.70 power of the Reynolds number is proposed to modify the scraping ratio in the present study. The synergy between the velocity and the pressure gradient is innovatively employed to research the tip clearance flow characteristics, and it gives a reliable criterion of indicating the flow patterns in the tip clearance.
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Sheard, A. G., S. G. O’Donnell, and J. F. Stringfellow. "High Temperature Proximity Measurement in Aero and Industrial Turbomachinery." Journal of Engineering for Gas Turbines and Power 121, no. 1 (January 1, 1999): 167–73. http://dx.doi.org/10.1115/1.2816305.
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The measurement of disc and shaft displacement has been performed for many years as part of the development, commissioning and monitoring of all classes of turbomachinery. This measurement has traditionally been performed using sensors that cannot operate above the curie point of rare earth magnets. In this paper a programme of work is described that was undertaken to develop a measurement system that could make a measurement of target proximity in a high temperature environment. The specific objectives were to make possible the measurement of turbine disc axial movement and shaft motion in the engine core, close to the combustion chamber or turbine; and secondly to make possible the measurement of tip clearance over shrouded turbine rotors.
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Donghyun You, Meng Wang, Rajat Mittal, and P. Moin. "Study of flow in tip-clearance turbomachines using large-eddy simulation." Computing in Science and Engineering 6, no. 6 (November 2004): 38–46. http://dx.doi.org/10.1109/mcse.2004.75.
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Horlock, J. H. "Secondary Flow in Repeating Stages of Axial Turbomachines." Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy 209, no. 2 (May 1995): 101–10. http://dx.doi.org/10.1243/pime_proc_1995_209_020_02.
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In a well-designed multi-stage axial flow compressor, the flow settles down to a repeating condition, in which the axial velocity profile does not deteriorate further; it is more or less unchanged between the entry and the exit of a deeply embedded stage. However, experimental data also show that the flow angles repeat, and it is this flow phenomenon that is discussed in the paper. Secondary flow analysis, coupled with empirical data on clearance flows, is used to give a description of the flow in such a repeating stage. The secondary flow at exit from a row involves both the streamwise vorticity generated in that row and the vorticity that exists at entry—the so-called ‘skew’ vorticity due to a non-uniform velocity from a stator being received by a moving rotor (and a similar effect from the rotor to the stator). However, clearance vorticity—shed from the rotor tip (casing) section and the stator root (hub) section—is also present and can be taken into account. Calculations made using the analyses are compared with some limited experimental data drawn from the published literature. Predicted underturning at rotor tip (casing) sections is confirmed by experiments; similarly, predicted underturning at stator tip (casing) sections accords with observations in one compressor but not in another. However, no universal conclusion (on whether underturning or overturning usually occurs) can be drawn for the flow through the rotor and stator root (hub) sections, as either entry or generated secondary vorticity may dominate.
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You, Donghyun, Meng Wang, Parviz Moin, and Rajat Mittal. "Vortex Dynamics and Low-Pressure Fluctuations in the Tip-Clearance Flow." Journal of Fluids Engineering 129, no. 8 (January 24, 2007): 1002–14. http://dx.doi.org/10.1115/1.2746911.
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The tip-clearance flow in axial turbomachines is studied using large-eddy simulation with particular emphasis on understanding the unsteady characteristics of the tip-leakage vortical structures and the underlying mechanisms for cavitation-inducing low-pressure fluctuations. A systematic and detailed analysis of the velocity and pressure fields has been made in a linear cascade with a moving end-wall. The generation and evolution of the tip-leakage vortical structures have been investigated throughout the cascade using mean streamlines and λ2 contours. An analysis of the energy spectra and space-time correlations of the velocity fluctuations suggests that the tip-leakage vortex is subject to a pitchwise low frequency wandering motion. Detailed statistics of the pressure fields has been analyzed to draw inferences on cavitation. The regions of low pressure relative to the mean values coincide with regions of strong pressure fluctuations, and the regions are found to be highly correlated with the vortical structures in the tip-leakage flow, particularly in the tip-leakage and tip-separation vortices.
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Sheard, A. G., G. C. Westerman, B. Killeen, and M. Fitzpatrick. "A High-Speed Capacitance-Based System for Gaging Turbomachinery Blading Radius During the Tip Grind Process." Journal of Engineering for Gas Turbines and Power 116, no. 1 (January 1, 1994): 243–49. http://dx.doi.org/10.1115/1.2906800.
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During the manufacture and overhaul of gas turbines, it is necessary to ensure that all blades in a stage are of an equal and known length to minimize the loss in performance that arises as a consequence of the clearance between rotor tip and engine casing. Modern compressor and turbine blades are generally loose fitting in their root fixings and only adopt their true working position when running. In this paper, a new technique for measuring the rotor radius over individual blades is described. The measurement technique utilizes a capacitance-based clearance measurement system, which enables rotor radius to be measured over each blade while spinning fast enough to ensure that the blades are centrifugally loaded into their true working position. The measurement technique is described, as is the system utilized to calibrate and reduce output into engineering units. The mechanical design of the “measurement head” is presented and the CNC lathe to which it interfaces described. Finally, the results of an experimental program, utilizing a fully bladed compressor disk undertaken to ascertain system performance, are presented.
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Senoo, Y. "Mechanics on the Tip Clearance Loss of Impeller Blades." Journal of Turbomachinery 113, no. 4 (October 1, 1991): 680–85. http://dx.doi.org/10.1115/1.2929134.
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For predicting the tip clearance loss of turbomachines, different equations are published in the literature based on different principles. In 1986 the present author postulated a new theory where the pressure loss consisted of two parts: the pressure loss induced by the drag force of the leaked flow, and the pressure loss to support the axial pressure difference without blades in the tip clearance zone. It has been suggested that the two losses were the same loss looked from two different viewpoints, or at least apart of the former was included in the latter or vice versa. In this paper the pressure loss due to the tip clearance is examined based on a macroscopic balance of forces, and the two kinds of loss are derived. Furthermore, it is shown that the former comes from the induced drag, which is parallel to the blade, while the latter comes from the missing blade force normal to the blade in the clearance zone. Because these two forces are mutally perpendicular, the two losses are entirely different in nature and they do not even partially overlap. It is also made clear quantitatively how the loss of the kinetic energy of leaked flow is related to the induced drag of the clearance flow.
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Parrish, C. J. "Fast Response Tip Clearance Measurements in Axial Flow Compressors—Techniques and Results." Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering 204, no. 1 (January 1990): 51–55. http://dx.doi.org/10.1243/pime_proc_1990_204_209_02.
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As part of an investigation of the effects of tip clearance performance of development axial flow compressors, a system for detecting rotor blade tip rubs has been developed and a tip clearance measuring system modified to detect clearance changes at a bandwidth of 500 Hz. Mean clearance changes have been measured as well as changes during surge. Rotor orbit has also been investigated and the system has become an important means of monitoring rotordynamic behaviour. Subharmonic components of rotor orbit have been discovered.
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Howard, M. A., P. C. Ivey, J. P. Barton, and K. F. Young. "Endwall Effects at Two Tip Clearances in a Multistage Axial Flow Compressor With Controlled Diffusion Blading." Journal of Turbomachinery 116, no. 4 (October 1, 1994): 635–45. http://dx.doi.org/10.1115/1.2929454.
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Effects of tip clearance, secondary flow, skew, and corner stall on the performance of a multistage compressor with controlled diffusion blading have been studied experimentally. Measurements between 1 and 99 percent annulus height were carried out in both the first and the third stages of a four-stage low-speed compressor with repeating-stage blading. Measurements were obtained at a datum rotor tip clearance and at a more aerodynamically desirable lower clearance. The consequences of the modified rotor tip clearance on both rotor and stator performance are examined in terms of loss coefficient and gas exit angle. Stator losses close to the casing are found to increase significantly when the clearance of an upstream rotor is increased. These increased stator losses cause 30 percent of the stage efficiency reduction that arises with increased rotor tip clearance. The deviation angles due to tip clearance from the multistage measurements are found to be similar to data from single-stage machines with conventional blading, which suggests that the unsteady flow phenomena associated with the multistage environment do not dominate the physics of the flow.
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Storer, J. A., and N. A. Cumpsty. "Tip Leakage Flow in Axial Compressors." Journal of Turbomachinery 113, no. 2 (April 1, 1991): 252–59. http://dx.doi.org/10.1115/1.2929095.
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Experimental measurements in a linear cascade with tip clearance are complemented by numerical solutions of the three-dimensional Navier–Stokes equations in an investigation of tip leakage flow. Measurements reveal that the clearance flow, which separates near the entry of the tip gap, remains unattached for the majority of the blade chord when the tip clearance is similar to that typical of a machine. The numerical predictions of leakage flow rate agree very well with measurements, and detailed comparisons show that the mechanism of tip leakage is primarily inviscid. It is demonstrated by simple calculation that it is the static pressure field near the end of the blade that controls chordwise distribution of the flow across the tip. Although the presence of a vortex caused by the roll-up of the leakage flow may affect the local pressure field, the overall magnitude of the tip leakage flow remains strongly related to the aerodynamic loading of the blades.
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Zierke, W. C., K. J. Farrell, and W. A. Straka. "Measurements of the Tip Clearance Flow for a High-Reynolds-Number Axial-Flow Rotor." Journal of Turbomachinery 117, no. 4 (October 1, 1995): 522–32. http://dx.doi.org/10.1115/1.2836564.
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A high-Reynolds-number pump (HIREP) facility has been used to acquire flow measurements in the rotor blade tip clearance region, with blade chord Reynolds numbers of 3,900,000 and 5,500,000. The initial experiment involved rotor blades with varying tip clearances, while a second experiment involved a more detailed investigation of a rotor blade row with a single tip clearance. The flow visualization on the blade surface and within the flow field indicate the existence of a trailing-edge separation vortex, a vortex that migrates radially upward along the trailing edge and then turns in the circumferential direction near the casing, moving in the opposite direction of blade rotation. Flow visualization also helps in establishing the trajectory of the tip leakage vortex core and shows the unsteadiness of the vortex. Detailed measurements show the effects of tip clearance size and downstream distance on the structure of the rotor tip leakage vortex. The character of the velocity profile along the vortex core changes from a jetlike profile to a wakelike profile as the tip clearance becomes smaller. Also, for small clearances, the presence and proximity of the casing endwall affects the roll-up, shape, dissipation, and unsteadiness of the tip leakage vortex. Measurements also show how much circulation is retained by the blade tip and how much is shed into the vortex, a vortex associated with high losses.
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Neuhaus, L., J. Schulz, W. Neise, and M. Möser. "Active control of the aerodynamic performance and tonal noise of axial turbomachines." Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy 217, no. 4 (January 1, 2003): 375–83. http://dx.doi.org/10.1243/095765003322315432.
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Two projects on axial fans are presented in this paper. The first aims at improving the aerodynamic performance and reducing the tip clearance noise caused by the rotating instability. This is achieved by injecting air into the radial gap between the impeller blade tips and the fan casing. Steady air injection with small mass flows results in remarkable reductions in the noise level along with improved aerodynamic performance. Larger injected mass flows give significant improvements in the aerodynamic performance at the expense of an increased overall noise level. The second project uses flow control actively to reduce the blade passage frequency (BPF) level. Experimental results are presented for steady jets injected into the main flow and cylindrical rods at axial positions downstream of the impeller blades. The method is successful for higher-order mode sound fields where the BPF level is reduced by up to 20.5 dB.
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Berdanier, Reid A., and Nicole L. Key. "Experimental Investigation of Factors Influencing Operating Rotor Tip Clearance in Multistage Compressors." International Journal of Rotating Machinery 2015 (2015): 1–13. http://dx.doi.org/10.1155/2015/146272.
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An analysis of compressor rotor tip clearance measurements using capacitance probe instrumentation is discussed for a three-stage axial compressor. Thermal variations and centrifugal effects related to rotational speed changes affect clearance heights relative to the assembled configuration. These two primary contributions to measured changes are discussed both independently and in combination. Emphasis is given to tip clearance changes due to changing loading condition and at several compressor operating speeds. Measurements show a tip clearance change approaching 0.1 mm (0.2% rotor span) when comparing a near-choke operating condition to a near-stall operating condition for the third stage. Additional consideration is given to environmental contributions such as ambient temperature, for which changes in tip clearance height on the order of 0.05 mm (0.1% rotor span) were noted for temperature variations of 15°C. Experimental compressor operating clearances are presented for several temperatures, operating speeds, and loading conditions, and comparisons are drawn between these measured variations and predicted changes under the same conditions.
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van de Wall, Allan G., Jaikrishnan R. Kadambi, and John J. Adamczyk. "A Transport Model for the Deterministic Stresses Associated With Turbomachinery Blade Row Interactions." Journal of Turbomachinery 122, no. 4 (February 1, 2000): 593–603. http://dx.doi.org/10.1115/1.1312802.
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The unsteady process resulting from the interaction of upstream vortical structures with a downstream blade row in turbomachines can have a significant impact on the machine efficiency. The upstream vortical structures or disturbances are transported by the mean flow of the downstream blade row, redistributing the time-average unsteady kinetic energy (K) associated with the incoming disturbance. A transport model was developed to take this process into account in the computation of time-averaged multistage turbomachinery flows. The model was applied to compressor and turbine geometry. For compressors, the K associated with upstream two-dimensional wakes and three-dimensional tip clearance flows is reduced as a result of their interaction with a downstream blade row. This reduction results from inviscid effects as well as viscous effects and reduces the loss associated with the upstream disturbance. Any disturbance passing through a compressor blade row results in a smaller loss than if the disturbance was mixed-out prior to entering the blade row. For turbines, the K associated with upstream two-dimensional wakes and three-dimensional tip clearance flows are significantly amplified by inviscid effects as a result of the interaction with a downstream turbine blade row. Viscous effects act to reduce the amplification of the K by inviscid effects but result in a substantial loss. Two-dimensional wakes and three-dimensional tip clearance flows passing through a turbine blade row result in a larger loss than if these disturbances were mixed-out prior to entering the blade row. [S0889-504X(00)01804-3]
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McNulty, G. Scott, John J. Decker, Brent F. Beacher, and S. Arif Khalid. "The Impact of Forward Swept Rotors on Tip Clearance Flows in Subsonic Axial Compressors." Journal of Turbomachinery 126, no. 4 (October 1, 2004): 445–54. http://dx.doi.org/10.1115/1.1773852.
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This paper presents an experimental and analytical study of the impact of forward swept rotors on tip-limited, low-speed, multistage axial compressors. Two different configurations were examined, one with strong tip-clearance flows and the other with more moderate levels. Evaluations were done at multiple rotor tip clearances to assess differences in clearance sensitivity. Compared to conventionally stacked radial rotors, the forward swept blades demonstrated improvements in stall margin, efficiency and clearance sensitivity. The benefits were more pronounced for the configuration with stronger tip-clearance flows. Detailed flow measurements and three-dimensional viscous CFD analyses were used to investigate the responsible flow mechanisms. Forward sweep causes a spanwise redistribution of flow toward the blade tip and reduces the tip loading in terms of static pressure coefficient. This results in reduced tip-clearance flow blockage, a shallower (more axial) vortex trajectory and a smaller region of reversed flow in the clearance gap.
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Prasad, Anil, and Joel H. Wagner. "Unsteady Effects in Turbine Tip Clearance Flows." Journal of Turbomachinery 122, no. 4 (February 1, 2000): 621–27. http://dx.doi.org/10.1115/1.1314608.
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The present study is concerned with the unsteady flow field on the blade outer air seal segments of high-work turbines; these segments are installed between the blade tip and outer casing and are usually subjected to extreme heat loads. Time-resolved measurements of the unsteady pressure on the blade outer air seal are made in a low-speed turbine rig. The present measurements indicate the existence of a separation zone on the blade tip, which causes a vena contracta to form at the entrance of the tip gap. In addition, a careful comparison between the ensemble-averaged pressure measurement and the corresponding result from steady computation suggests that the pressure on the blade outer air seal can largely be described as being due to a steady flow (in the rotating frame) sweeping past a stationary probe. The ensemble deviation measurement indicates that unsteadiness (from one revolution to the next) is confined to the tip gap. [S0889-504X(00)02304-7]
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Steiner, Alexander. "Techniques for blade tip clearance measurements with capacitive probes." Measurement Science and Technology 11, no. 7 (June 16, 2000): 865–69. http://dx.doi.org/10.1088/0957-0233/11/7/303.
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Heyes, F. J. G., and H. P. Hodson. "Erratum: “Measurement and Prediction of Tip Clearance Flow in Linear Turbine Cascades” (Journal of Turbomachinery, 1993, 115, p. 376–382)." Journal of Turbomachinery 115, no. 4 (October 1, 1993): 698. http://dx.doi.org/10.1115/1.2929304.
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Teng, Shuye, Je-Chin Han, and G. M. S. Azad. "Detailed Heat Transfer Coefficient Distributions on a Large-Scale Gas Turbine Blade Tip." Journal of Heat Transfer 123, no. 4 (December 5, 2000): 803–9. http://dx.doi.org/10.1115/1.1373655.
Full textAbstract:
Measurements of detailed heat transfer coefficient distributions on a turbine blade tip were performed in a large-scale, low-speed wind tunnel facility. Tests were made on a five-blade linear cascade. The low-speed wind tunnel is designed to accommodate the 107.49 deg turn of the blade cascade. The mainstream Reynolds number based on cascade exit velocity was 5.3×105. Upstream unsteady wakes were simulated using a spoke-wheel type wake generator. The wake Strouhal number was kept at 0 or 0.1. The central blade had a variable tip gap clearance. Measurements were made at three different tip gap clearances of about 1.1 percent, 2.1 percent, and 3 percent of the blade span. Static pressure distributions were measured in the blade mid-span and on the shroud surface. Detailed heat transfer coefficient distributions were measured on the blade tip surface using a transient liquid crystal technique. Results show that reduced tip clearance leads to reduced heat transfer coefficient over the blade tip surface. Results also show that reduced tip clearance tends to weaken the unsteady wake effect on blade tip heat transfer.
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Jin, P., and R. J. Goldstein. "Local Mass/Heat Transfer on Turbine Blade Near-Tip Surfaces." Journal of Turbomachinery 125, no. 3 (July 1, 2003): 521–28. http://dx.doi.org/10.1115/1.1554410.
Full textAbstract:
Local mass transfer measurements on a simulated high-pressure turbine blade are conducted in a linear cascade with tip clearance, using a naphthalene sublimation technique. The effects of tip clearance (0.86–6.90% of chord) are investigated at an exit Reynolds number of 5.8×105 and a low turbulence intensity of 0.2%. The effects of the exit Reynolds number 4−7×105 and the turbulence intensity (0.2 and 12.0%) are also measured for the smallest tip clearance. The effect of tip clearance on the mass transfer on the pressure surface is limited to 10% of the blade height from the tip at smaller tip clearances. At the largest tip clearance high mass transfer rates are induced at 15% of curvilinear distance Sp/C by the strong acceleration of the fluid on the pressure side into the clearance. The effect of tip clearance on the mass transfer is not very evident on the suction surface for curvilinear distance of Ss/C<0.21. However, much higher mass transfer rates are caused downstream of Ss/C≈0.50 by the tip leakage vortex at the smallest tip clearance, while at the largest tip clearance, the average mass transfer is lower than that with zero tip clearance, probably because the strong leakage vortex pushes the passage vortex away from the suction surface. High mainstream turbulence level (12.0%) increases the local mass transfer rates on the pressure surface, while a higher mainstream Reynolds number generates higher local mass transfer rates on both near-tip surfaces.
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Storace, A. F., D. C. Wisler, H. W. Shin, B. F. Beacher, F. F. Ehrich, Z. S. Spakovszky, M. Martinez-Sanchez, and S. J. Song. "Unsteady Flow and Whirl-Inducing Forces in Axial-Flow Compressors: Part I—Experiment." Journal of Turbomachinery 123, no. 3 (February 1, 2000): 433–45. http://dx.doi.org/10.1115/1.1378299.
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An experimental and theoretical investigation has been conducted to evaluate the effects seen in axial-flow compressors when the centerline of the rotor is displaced from the centerline of the static structure of the engine. This creates circumferentially nonuniform rotor-tip clearances, unsteady flow, and potentially increased clearances if the rotating and stationary parts come in contact. The result not only adversely affects compressor stall margin, pressure rise capability, and efficiency, but also generates an unsteady, destabilizing, aerodynamic force, called the Thomas/Alford force, which contributes significantly to rotor whirl instabilities in turbomachinery. Determining both the direction and magnitude of this force in compressors, relative to those in turbines, is especially important for the design of mechanically stable turbomachinery components. Part I of this two-part paper addresses these issues experimentally and Part II presents analyses from relevant computational models. Our results clearly show that the Thomas/Alford force can promote significant backward rotor whirl over much of the operating range of modern compressors, although some regions of zero and forward whirl were found near the design point. This is the first time that definitive measurements, coupled with compelling analyses, have been reported in the literature to resolve the long-standing disparity in findings concerning the direction and magnitude of whirl-inducing forces important in the design of modern axial-flow compressors.
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El-Batsh, Hesham M., and Magdy Bassily Hanna. "An Investigation on the Effect of Endwall Movement on the Tip Clearance Loss Using Annular Turbine Cascade." International Journal of Rotating Machinery 2011 (2011): 1–11. http://dx.doi.org/10.1155/2011/489150.
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The aerodynamic losses in gas turbines are mainly caused by profile loss secondary flow, and tip leakage loss. This study focuses on tip leakage flow of high-pressure turbine stages. An annular turbine cascade was constructed with fixed blades on the casing, and the distance between blade tip and the hub was considered as tip clearance gap. The effect of endwall movement on loss mechanism was investigated by using experimental and numerical techniques. The measurements were obtained while the hub was fixed but the numerical calculations were carried out for both stationary and moving cascades. Upstream and downstream flows were measured by using a calibrated five-hole pressure probe. The steady incompressible turbulent flow was obtained by solving Reynolds averaged Navier-Stokes equations and by employing shear stress transport (SST)k-ωturbulence model. The total pressure loss coefficient obtained from the numerical technique was compared with the experimental measurements, and the comparison showed good agreement. Tip clearance vortices were observed in the tip clearance gap. It was found through this study that end-wall movement reduces tip leakage loss through the cascade.
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Sheard, A. G. "Blade by Blade Tip Clearance Measurement." International Journal of Rotating Machinery 2011 (2011): 1–13. http://dx.doi.org/10.1155/2011/516128.
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This paper describes a capacitance-based tip clearance measurement system which engineers have used in the most demanding turbine test applications. The capacitance probe has survived extended use in a major European gas turbine manufacturer's high-temperature demonstrator unit, where it functioned reliably at a turbine entry temperature in excess of 1800 degrees Kelvin. This paper explores blade by blade tip clearance measurement techniques and examines probe performance under laboratory conditions in support of high-temperature installations. The paper outlines the blade by blade tip clearance measurement technique and describes the experimental facility used to study tip clearance measurement. The paper also fully describes the method used to calibrate the measurement system in order to ascertain measurement accuracy. The paper clarifies how the practical problems were overcome associated with making blade by blade tip clearance measurements in both compressor and turbine environments. Since its initial development, gas turbine development programmes have routinely used the clearance measurement system. The inherent robustness of the system has resulted in reliable in-service measurement of clearance in real world applications.
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Lakshminarayana, B., M. Zaccaria, and B. Marathe. "The Structure of Tip Clearance Flow in Axial Flow Compressors." Journal of Turbomachinery 117, no. 3 (July 1, 1995): 336–47. http://dx.doi.org/10.1115/1.2835667.
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Detailed measurements of the flow field in the tip region of an axial flow compressor rotor were carried out using a rotating five-hole probe. The axial, tangential, and radial components of relative velocity, as well as the static and stagnation pressures, were obtained at two axial locations, one at the rotor trailing edge, the other downstream of the rotor. The measurements were taken up to about 26 percent of the blade span from the blade tip. The data are interpreted to understand the complex nature of the flow in the tip region, which involves the interaction of the tip leakage flow, the annulus wall boundary layer and the blade wake. The experimental data show that the leakage jet does not roll up into a vortex. The leakage jet exiting from the tip gap is of high velocity and mixes quickly with the mainstream, producing intense shearing and flow separation. There are substantial differences in the structure of tip clearance observed in cascades and rotors.
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Srinivasan, V., and R. J. Goldstein. "Effect of Endwall Motion on Blade Tip Heat Transfer." Journal of Turbomachinery 125, no. 2 (April 1, 2003): 267–73. http://dx.doi.org/10.1115/1.1554411.
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Local mass transfer measurements were conducted on the tip of a turbine blade in a five-blade linear cascade with a blade-centered configuration. The tip clearance levels ranged from 0.6 to 6.9% of blade chord. The effect of relative motion between the casing and the blade tip was simulated using a moving endwall made of neoprene mounted on the top of the wind tunnel. Data were obtained for a single Reynolds number of 2.7×105 based on cascade exit velocity and blade chord. Pressure measurements indicate that the effect of endwall motion on blade loading at a clearance of 0.6% of blade chord is to reduce the pressure gradients driving the tip leakage flow. With the introduction of endwall motion, there is a reduction of about 9% in mass transfer levels at a clearance of 0.6% of chord. This is presumably due to the tip leakage vortex coming closer to the suction side of the blade and ‘blocking the flow,’ leading to reduced tip gap velocities and hence lower mass transfer.
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Jin, P., and R. J. Goldstein. "Local Mass and Heat Transfer on a Turbine Blade Tip." International Journal of Rotating Machinery 9, no. 2 (2003): 81–95. http://dx.doi.org/10.1155/s1023621x03000083.
Full textAbstract:
Local mass and heat transfer measurements on a simulated high-pressure turbine blade-tip surface are conducted in a linear cascade with a nonmoving tip endwall, using a naphthalene sublimation technique. The effects of tip clearance (0.86–6.90% of chord) are investigated at various exit Reynolds numbers (4–7 ×105) and turbulence intensities (0.2 and 12.0%).The mass transfer on the tip surface is significant along its pressure edge at the smallest tip clearance. At the two largest tip clearances, the separation bubble on the tip surface can cover the whole width of the tip on the second half of the tip surface. The average mass-transfer rate is highest at a tip clearance of 1.72% of chord. The average mass-transfer rate on the tip surface is four and six times as high as on the suction and the pressure surface, respectively. A high mainstream turbulence level of 12.0% reduces average mass-transfer rates on the tip surface, while the higher mainstream Reynolds number generates higher local and average mass-transfer rates on the tip surface.
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Borovik, S. Yu, M. M. Kuteynikova, P. E. Podlipnov, B. K. Raykov, Yu N. Sekisov, and O. P. Skobelev. "Adjacent Blades' Effect on the Tip Clearance Measurements in Turbines." MEHATRONIKA, AVTOMATIZACIA, UPRAVLENIE 16, no. 5 (May 18, 2015): 327–36. http://dx.doi.org/10.17587/mau.16.327-336.
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Yaras, M. I., S. A. Sjolander, and R. J. Kind. "Effects of Simulated Rotation on Tip Leakage in a Planar Cascade of Turbine Blades: Part II—Downstream Flow Field and Blade Loading." Journal of Turbomachinery 114, no. 3 (July 1, 1992): 660–67. http://dx.doi.org/10.1115/1.2929190.
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This paper and its companion paper present experimental results on the effects of simulated rotation on the tip leakage in a linear turbine cascade test. Part II examines the downstream flow field. For clearance sizes of 2.4 and 3.8 percent of the blade chord, measurements were made in two planes downstream of the trailing edge using a seven-hole pressure probe. Significant changes in the tip leakage vortex and passage vortex structures are observed with the introduction of relative motion. The effects of clearance size and rotation on the relationship between bound circulation and tip-vortex circulation are discussed. The validity of a previously developed tip-vortex model for the case of rotation is examined in the light of the measurements. Finally, for clearances of 1.5, 2.4, and 3.8 percent of the blade chord, the effects of rotation on blade loading are studied through static pressure measurements on the blade surfaces. The distortion of the surface pressure field near the tip is found to be reduced with increasing wall speed. This is consistent with the reduced strength of the tip-leakage vortex as wall speed is increased. For all measurements two wall speeds are considered and the results are compared with the case of no rotation.
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Azad, Gm S., Je-Chin Han, Shuye Teng, and Robert J. Boyle. "Heat Transfer and Pressure Distributions on a Gas Turbine Blade Tip." Journal of Turbomachinery 122, no. 4 (February 1, 2000): 717–24. http://dx.doi.org/10.1115/1.1308567.
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Heat transfer coefficient and static pressure distributions are experimentally investigated on a gas turbine blade tip in a five-bladed stationary linear cascade. The blade is a two-dimensional model of a first-stage gas turbine rotor blade with a blade tip profile of a GE-E3 aircraft gas turbine engine rotor blade. The flow condition in the test cascade corresponds to an overall pressure ratio of 1.32 and exit Reynolds number based on axial chord of 1.1×106. The middle 3-blade has a variable tip gap clearance. All measurements are made at three different tip gap clearances of about 1, 1.5, and 2.5 percent of the blade span. Heat transfer measurements are also made at two different turbulence intensity levels of 6.1 and 9.7 percent at the cascade inlet. Static pressure measurements are made in the midspan and the near-tip regions as well as on the shroud surface, opposite the blade tip surface. Detailed heat transfer coefficient distributions on the plane tip surface are measured using a transient liquid crystal technique. Results show various regions of high and low heat transfer coefficient on the tip surface. Tip clearance has a significant influence on local tip heat transfer coefficient distribution. Heat transfer coefficient also increases about 15–20 percent along the leakage flow path at higher turbulence intensity level of 9.7 over 6.1 percent. [S0889-504X(00)00404-9]
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Kang, S., and C. Hirsch. "Experimental Study on the Three-Dimensional Flow Within a Compressor Cascade With Tip Clearance: Part I—Velocity and Pressure Fields." Journal of Turbomachinery 115, no. 3 (July 1, 1993): 435–43. http://dx.doi.org/10.1115/1.2929270.
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Experimental results from a study of the three-dimensional flow in a linear compressor cascade with stationary endwall at design conditions are presented for tip clearance levels of 1.0, 2.0, and 3.3 percent of chord, compared with the no-clearance case. In addition to five-hole probe measurements, extensive surface flow visualizations are conducted. It is observed that for the smaller clearance cases a weak horseshoe vortex forms in the front of the blade leading edge. At all the tip gap cases, a multiple tip vortex structure with three discrete vortices around the midchord is found. The tip leakage vortex core is well defined after the midchord but does not cover a significant area in traverse planes. The presence of the tip leakage vortex results in the passage vortex moving close to the endwall and the suction side.
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Khalid, S. A., A. S. Khalsa, I. A. Waitz, C. S. Tan, E. M. Greitzer, N. A. Cumpsty, J. J. Adamczyk, and F. E. Marble. "Endwall Blockage in Axial Compressors." Journal of Turbomachinery 121, no. 3 (July 1, 1999): 499–509. http://dx.doi.org/10.1115/1.2841344.
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This paper presents a new methodology for quantifying compressor endwall blockage and an approach, using this quantification, for defining the links between design parameters, flow conditions, and the growth of blockage due to tip clearance flow. Numerical simulations, measurements in a low-speed compressor, and measurements in a wind tunnel designed to simulate a compressor clearance flow are used to assess the approach. The analysis thus developed allows predictions of endwall blockage associated with variations in tip clearance, blade stagger angle, inlet boundary layer thickness, loading level, loading profile, solidity, and clearance jet total pressure. The estimates provided by this simplified method capture the trends in blockage with changes in design parameters to within 10 percent. More importantly, however, the method provides physical insight into, and thus guidance for control of, the flow features and phenomena responsible for compressor endwall blockage generation.
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Papa, M., R. J. Goldstein, and F. Gori. "Effects of Tip Geometry and Tip Clearance on the Mass/Heat Transfer From a Large-Scale Gas Turbine Blade." Journal of Turbomachinery 125, no. 1 (January 1, 2003): 90–96. http://dx.doi.org/10.1115/1.1529190.
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An experimental investigation has been performed to measure average and local mass transfer coefficients on the tip of a gas turbine blade using the naphthalene sublimation technique. The heat/mass transfer analogy can be applied to obtain heat transfer coefficients from the measured mass transfer data. Flow visualization on the tip surface is provided using an oil dot technique. Two different tip geometries are considered: a squealer tip and a winglet-squealer tip having a winglet on the pressure side and a squealer on the suction side of the blade. Measurements have been taken at tip clearance levels ranging from 0.6 to 3.6% of actual chord. The exit Reynolds number based on actual chord is approximately 7.2×105 for all measurements. Flow visualization shows impingement and recirculation regions on the blade tip surface, providing an interpretation of the mass transfer distributions and offering insight into the fluid dynamics within the gap. For both tip geometries the tip clearance level has a significant effect on the mass transfer distribution. The squealer tip has a higher average mass transfer that sensibly decreases with gap level, whereas a more limited variation with gap level is observed for the average mass transfer from the winglet-squealer tip.
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Suder, K. L., and M. L. Celestina. "Experimental and Computational Investigation of the Tip Clearance Flow in a Transonic Axial Compressor Rotor." Journal of Turbomachinery 118, no. 2 (April 1, 1996): 218–29. http://dx.doi.org/10.1115/1.2836629.
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Experimental and computational techniques are used to investigate tip clearance flows in a transonic axial compressor rotor at design and part-speed conditions. Laser anemometer data acquired in the endwall region are presented for operating conditions near peak efficiency and near stall at 100 percent design speed and at near peak efficiency at 60 percent design speed. The role of the passage shock/leakage vortex interaction in generating endwall blockage is discussed. As a result of the shock/vortex interaction at design speed, the radial influence of the tip clearance flow extends to 20 times the physical tip clearance height. At part speed, in the absence of the shock, the radial extent is only five times the tip clearance height. Both measurements and analysis indicate that under part-speed operating conditions a second vortex, which does not originate from the tip leakage flow, forms in the end-wall region within the blade passage and exits the passage near midpitch. Mixing of the leakage vortex with the primary flow downstream of the rotor at both design and part-speed conditions is also discussed.
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García, Iker, Joseba Zubia, Josu Beloki, Jon Arrue, Gaizka Durana, and Gotzon Aldabaldetreku. "Optical Tip Clearance Measurements as a Tool for Rotating Disk Characterization." Sensors 17, no. 12 (January 15, 2017): 165. http://dx.doi.org/10.3390/s17010165.
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Graham, J. A. H. "Investigation of a Tip Clearance Cascade in a Water Analogy Rig." Journal of Engineering for Gas Turbines and Power 108, no. 1 (January 1, 1986): 38–46. http://dx.doi.org/10.1115/1.3239883.
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The tip clearance flow region of high-pressure axial turbine blades for small gas turbine engines has been investigated in a water flow cascade. The blade model features variable clearance and variable endwall speeds. The cascade is scaled for Reynolds number and sized to give velocities suitable for visualization. Pressure profiles were measured on one blade, and correlated with the visualization. Unloading is found to be a major feature of the pressure field at both tip and midspan, and is intimately connected with scraping effects and the behavior of the clearance vortex. Some initial hot-film velocity measurements are also presented.
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Yamamoto, A. "Interaction Mechanisms Between Tip Leakage Flow and the Passage Vortex in a Linear Turbine Rotor Cascade." Journal of Turbomachinery 110, no. 3 (July 1, 1988): 329–38. http://dx.doi.org/10.1115/1.3262201.
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In order to study the loss generation mechanisms due to the tip-leakage flow in turbine rotor passages, extensive traverse measurements were made of the three-dimensional flows in a low-speed linear cascade for various tip-clearance sizes and for various cascade inlet flow angles (or incidences). Effects of the leakage flow on the cascade downstream flow fields and interactions between the leakage flow and the passage vortices are discussed in detail based on the traverse measurements and flow-visualization tests in terms of secondary flows and the associated losses. Other traverses were also performed of the tip-casing endwall flows both inside and outside the tip-clearance gap using a micro five-hole pitot tube to reveal the axial development of the interaction throughout the cascade passage. Overall loss characteristics of the present high-turning cascade with blunt leading and trailing edges are obtained and compared with those predicted by the Ainley–Mathieson method.
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Durana, Gaizka, Josu Amorebieta, Ruben Fernandez, Josu Beloki, Eneko Arrospide, Iker Garcia, and Joseba Zubia. "Design, Fabrication and Testing of a High-Sensitive Fibre Sensor for Tip Clearance Measurements." Sensors 18, no. 8 (August 9, 2018): 2610. http://dx.doi.org/10.3390/s18082610.
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A highly sensitive fibre bundle-based reflective optical sensor has been designed and fabricated for Tip Clearance measurements in a turbine rig. The sensor offers high spatial and temporal resolution. The sensor probe consists of a single-mode transmitting fibre and two concentric rings of receiving multimode fibres that collect reflected light in a differential detection gain configuration, yielding a highly linear calibration curve for distance measurements. The clearance measurement range is approximately 2 mm around the central point fixed at 3.2 mm from the probe tip, and the sensitivity of the probe is 61.73 mm−1. The fibre bundle has been designed to ensure that the distance security specifications required for the experimental program of the turbine are met. The optical sensor has operated under demanding conditions set by the blade and casing design. The experimental results obtained so far are promising and lead us to think that the optical sensor has great potential for online clearance measurements with high precision.
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Sjolander, S. A., and K. K. Amrud. "Effects of Tip Clearance on Blade Loading in a Planar Cascade of Turbine Blades." Journal of Turbomachinery 109, no. 2 (April 1, 1987): 237–44. http://dx.doi.org/10.1115/1.3262090.
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The paper examines in detail the structure of the tip leakage flow and its effect on the blade loading in a large-scale planar cascade of turbine blades. The tip clearance was varied from 0.0 to 2.86 percent of the blade chord. One of the blades is instrumented with 14 rows of 73 static taps which allowed a very detailed picture of the loading near the tip to be obtained. In addition to the measurements, extensive flow visualization was conducted using both smoke and surface oil flow. A new feature found in the present experiment was the formation of multiple, discrete tip-leakage vortices as the clearance was increased. Their presence is clearly evident from the surface oil flow and they account for the multiple suction peaks found in the blade pressure distributions. Integration of the pressure distributions showed that for larger values of the clearance the blade loading increases as the tip is approached and only begins to decline very near the tip. The increase was found to occur primarily in the axial component of the force.