To see the other types of publications on this topic, follow the link: Leakage flows.
Journal articles on the topic 'Leakage flows'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 journal articles for your research on the topic 'Leakage flows.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse journal articles on a wide variety of disciplines and organise your bibliography correctly.
1
Lin, Feng, and Jingyi Chen. "Oscillatory Tip Leakage Flows and Stability Enhancement in Axial Compressors." International Journal of Rotating Machinery 2018 (June 6, 2018): 1–14. http://dx.doi.org/10.1155/2018/9076472.
Full textAbstract:
Rotating stall axial compressor is a difficult research field full of controversy. Over the recent decades, the unsteady tip leakage flows had been discovered and confirmed by several research groups independently. This paper summarizes the research experience on unsteady tip leakage flows and stability enhancement in axial flow compressors. The goal is to provide theoretical bases to design casing treatments and tip air injection for stall margin extension of axial compressor. The research efforts cover (1) the tip flow structure at near stall that can explain why the tip leakage flows go unsteady and (2) the computational and experimental evidences that demonstrate the axial momentum playing an important role in unsteady tip leakage flow. It was found that one of the necessary conditions for tip leakage flow to become unsteady is that a portion of the leakage flow impinges onto the pressure side of the neighboring blade near the leading edge. The impediment of the tip leakage flow against the main incoming flow can be measured by the axial momentum balance within the tip range. With the help of the theoretical progress, the applications are extended to various casing treatments and tip air recirculation.
2
Moore, J., and K. M. Elward. "Shock Formation in Overexpanded Tip Leakage Flow." Journal of Turbomachinery 115, no. 3 (July 1, 1993): 392–99. http://dx.doi.org/10.1115/1.2929266.
Full textAbstract:
Shock formation due to overexpansion of supersonic flow at the inlet to the tip clearance gap of a turbomachine has been studied. The flow was modeled on a water table using a sharp-edged rectangular channel. The flow exhibited an oblique hydraulic jump starting on the channel sidewall near the channel entrance. This flow was analyzed using hydraulic theory. The results suggest a model for the formation of the jump. The hydraulic analogy between free surface water flows and compressible gas flows is used to predict the location and strength of oblique shocks in analogous tip leakage flows. Features of the flow development are found to be similar to those of compressible flow in sharp-edged orifices. Possible implications of the results for high-temperature gas turbine design are considered.
3
Basson, A., and B. Lakshminarayana. "Numerical Simulation of Tip Clearance Effects in Turbomachinery." Journal of Turbomachinery 117, no. 3 (July 1, 1995): 348–59. http://dx.doi.org/10.1115/1.2835668.
Full textAbstract:
The numerical formulation developed here includes an efficient grid generation scheme, particularly suited to computational grids for the analysis of turbulent turbo-machinery flows and tip clearance flows, and a semi-implicit, pressure-based computational fluid dynamics scheme that directly includes artificial dissipation, and is applicable to both viscous and inviscid flows. The value of this artificial dissipation is optimized to achieve accuracy and convergency in the solution. The numerical model is used to investigate the structure of tip clearance flows in a turbine nozzle. The structure of leakage flow is captured accurately, including blade-to-blade variation of all three velocity components, pitch and yaw angles, losses and blade static pressures in the tip clearance region. The simulation also includes evaluation of such quantities as leakage mass flow, vortex strength, losses, dominant leakage flow regions, and the spanwise extent affected by the leakage flow. It is demonstrated, through optimization of grid size and artificial dissipation, that the tip clearance flow field can be captured accurately.
4
Gao, J., Q. Zheng, G. Yue, and L. Sun. "Control of shroud leakage flows to reduce mixing losses in a shrouded axial turbine." Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 226, no. 5 (October 3, 2011): 1263–77. http://dx.doi.org/10.1177/0954406211423324.
Full textAbstract:
The losses caused by the leakage flows through the rotor tip clearance, and the mixing losses by the re-entering leakage into the main flow are considerable parts of the total losses in turbines. The main reason for the mixing losses is the different velocity components of main and leakage flows. This leads to shear stresses which cause increased turbulence and losses. This article presents a numerical investigation on three different configurations to control the leakage flows: (a) turning vanes are fixed onto the casing between the fins to turn the shroud leakage flow into the main flow direction in order to reduce the circumferential mixing losses; (b) honeycomb bands are inserted into the casing to weaken the leakage flow in the circumferential direction and reduce the circumferential mixing losses due to the special hexagon structure; and (c) downstream edge of the cavity is chamfered to reduce the radial velocity component of the leakage jet and the separation at the downstream edge, and also to reduce the streamwise mixing losses. A 1.5-stage axial turbine with high-aspect ratio blading was used in this study to investigate the sealing designs as mentioned. The flow simulation results of the three configurations were analysed and compared in this article.
5
Ranson, W. W., K. A. Thole, and F. J. Cunha. "Adiabatic Effectiveness Measurements and Predictions of Leakage Flows Along a Blade Endwall." Journal of Turbomachinery 127, no. 3 (January 18, 2005): 609–18. http://dx.doi.org/10.1115/1.1929809.
Full textAbstract:
Traditional cooling schemes have been developed to cool turbine blades using high-pressure compressor air that bypasses the combustor. This high-pressure forces cooling air into the hot main gas path through seal slots. While parasitic leakages can provide a cooling benefit, they also represent aerodynamic losses. The results from the combined experimental and computational studies reported in this paper address the cooling benefit from leakage flows that occur along the platform of a first stage turbine blade. A scaled-up, blade geometry with an upstream slot, a mid-passage slot, and a downstream slot was tested in a linear cascade placed in a low-speed wind tunnel. Results show that the leakage flow through the mid-passage gap provides only a small cooling benefit to the platform. There is little to no benefit to the blade platform that results by increasing the coolant flow through the mid-passage gap. Unlike the mid-passage gap, leakage flow from the upstream slot provides good cooling to the platform surface, particularly in certain regions of the platform. Relatively good agreement was observed between the computational and experimental results, although computations overpredicted the cooling.
6
Tallman, J., and B. Lakshminarayana. "Numerical Simulation of Tip Leakage Flows in Axial Flow Turbines, With Emphasis on Flow Physics: Part I—Effect of Tip Clearance Height." Journal of Turbomachinery 123, no. 2 (February 1, 2000): 314–23. http://dx.doi.org/10.1115/1.1368881.
Full textAbstract:
A pressure-correction based, 3D Navier-Stokes CFD code was used to simulate the effects of turbine parameters on the tip leakage flow and vortex in a linear turbine cascade to understand the detailed flow physics. A baseline case simulation of a cascade was first conducted in order to validate the numerical procedure with experimental measurements. The effects of realistic tip clearance spacing, inlet conditions, and relative endwall motion were then sequentially simulated, while maintaining previously modified parameters. With each additional simulation, a detailed comparison of the leakage flow’s direction, pressure gradient, and mass flow, as well as the leakage vortex and its roll-up, size, losses, location, and interaction with other flow features, was conducted. Part I of this two-part paper focuses on the effect of reduced tip clearance height on the leakage flow and vortex. Reduced tip clearance results in less mass flow through the gap, a smaller leakage vortex, and less aerothermal losses in both the gap and the vortex. The shearing of the leakage jet and passage flow to which leakage vortex roll-up is usually attributed to is not observed in any of the simulations. Alternative explanations of the leakage vortex’s roll-up are presented. Additional secondary flows that are seen near the casing are also discussed.
7
Du, Hui, Xianjun Yu, and Baojie Liu. "Modeling of the double leakage and leakage spillage flows in axial flow compressors." Journal of Thermal Science 23, no. 2 (March 11, 2014): 103–13. http://dx.doi.org/10.1007/s11630-014-0683-9.
Full text
8
Sivo, J. M., A. J. Acosta, C. E. Brennen, and T. K. Caughey. "The Influence of Swirl Brakes on the Rotordynamic Forces Generated by Discharge-to-Suction Leakage Flows in Centrifugal Pumps." Journal of Fluids Engineering 117, no. 1 (March 1, 1995): 104–8. http://dx.doi.org/10.1115/1.2816797.
Full textAbstract:
Increasing interest has been given to swirl brakes as a means of reducing destabilizing rotordynamic forces due to leakage flows in new high speed rocket turbo-pumps. Although swirl brakes have been used successfully in practice (such as with the Space Shuttle HPOTP), no experimental tests until now have been performed to demonstrate their beneficial effect over a range of leakage flow rates. The present study investigates the effect of swirl brakes on rotordynamic forces generated by discharge-to-suction leakage flows in the annulus of shrouded centrifugal pumps over a range of subsynchronous whirl ratios and various leakage flow rates. In addition, the effectiveness of swirl brakes in the presence of leakage inlet (pump discharge) swirl is also demonstrated. The experimental data demonstrates that with the addition of swirl brakes a significant reduction in the destabilizing tangential force for lower flow rates is achieved. At higher flow rates, the brakes are detrimental. In the presence of leakage inlet swirl, brakes were effective over all leakage flow rates tested in reducing the range of whirl frequency ratio for which the tangential force is destabilizing.
9
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.
Full textAbstract:
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.
10
Tallman, J., and B. Lakshminarayana. "Numerical Simulation of Tip Leakage Flows in Axial Flow Turbines, With Emphasis on Flow Physics: Part II—Effect of Outer Casing Relative Motion." Journal of Turbomachinery 123, no. 2 (February 1, 2000): 324–33. http://dx.doi.org/10.1115/1.1369113.
Full textAbstract:
A pressure-correction based, 3D Navier-Stokes CFD code was used to simulate the effects of turbine parameters on the tip leakage flow and vortex in a linear turbine cascade to understand the detailed flow physics. A baseline case simulation of a cascade was first conducted in order to validate the numerical procedure with experimental measurements. The effects of realistic tip clearance spacing, inlet conditions, and relative endwall motion were then sequentially simulated, while maintaining previously modified parameters. With each additional simulation, a detailed comparison of the leakage flow’s direction, pressure gradient, and mass flow, as well as the leakage vortex and its roll-up, size, losses, location, and interaction with other flow features, was conducted. Part II of this two-part paper series focuses on the effect of relative motion of the outer casing on the leakage flow and vortex development. Casing relative motion results in less mass flow through the gap and a smaller leakage vortex. The structure of the aerothermal losses in the passage change dramatically when the outer casing motion was incorporated, but the total losses in the passage remained very similar. Additional secondary flows that are seen near the casing are also discussed.
11
Guinzburg, A., C. E. Brennen, A. J. Acosta, and T. K. Caughey. "The Effect of Inlet Swirl on the Rotordynamic Shroud Forces in a Centrifugal Pump." Journal of Engineering for Gas Turbines and Power 115, no. 2 (April 1, 1993): 287–93. http://dx.doi.org/10.1115/1.2906707.
Full textAbstract:
The role played by fluid forces in determining the rotordynamic stability of a centrifugal pump is gaining increasing attention. The present research investigates the contributions to the rotordynamic forces from the discharge-to-suction leakage flows between the front shroud of the rotating impeller and the stationary pump casing. In particular, the dependency of the rotordynamic characteristics of leakage flows on the swirl at the inlet to the leakage path was examined. An inlet guide vane was designed for the experiment so that swirl could be introduced at the leakage flow inlet. The data demonstrate substantial rotordynamic effects and a destabilizing tangential force for small positive whirl ratios; this force decreased with increasing flow rate. The effect of swirl on the rotordynamic forces was found to be destabilizing.
12
Wellborn, S. R., and T. H. Okiishi. "The Influence of Shrouded Stator Cavity Flows on Multistage Compressor Performance." Journal of Turbomachinery 121, no. 3 (July 1, 1999): 486–97. http://dx.doi.org/10.1115/1.2841341.
Full textAbstract:
Experiments were performed on a low-speed multistage axial-flow compressor to assess the effects of shrouded stator cavity flows on aerodynamic performance. Five configurations, which involved systematic changes in seal-tooth leakage rates and/or elimination of the shrouded stator cavities, were tested. Rig data indicate increasing seal-tooth leakage substantially degraded compressor performance. For every 1 percent increase in seal-tooth clearance-to-span ratio, the decrease in pressure rise was 3 percent and the reduction in efficiency was 1 point. These observed performance penalties are comparable to those commonly reported for rotor and cantilevered stator tip clearance variations. The performance degradation observed with increased leakage was brought about in two distinct ways. First, increasing seal-tooth leakage directly spoiled the near-hub performance of the stator row in which leakage occurred. Second, the altered stator exit flow conditions, caused by increased leakage, impaired the performance of the next downstream stage by decreasing the work input of the rotor and increasing total pressure loss of the stator. These trends caused the performance of downstream stages to deteriorate progressively. Numerical simulations of the test rig stator flow field were also conducted to help resolve important fluid mechanic details associated with the interaction between the primary and cavity flows. Simulation results show that fluid originating in the upstream cavity collected on the stator suction surface when the cavity tangential momentum was low and on the pressure side when it was high. The convection of cavity fluid to the suction surface was a mechanism that reduced stator performance when leakage increased.
13
Lee, Y. L. "Effects of body leakage on ventilation and wind noise around a sunroof." Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering 216, no. 5 (May 1, 2002): 363–71. http://dx.doi.org/10.1243/0954407021529174.
Full textAbstract:
Some passenger cars with sunroofs open at tilted positions experience reverse flows into cabin rooms and wind noises much louder than in other cars. In this study, flows around an open tilted sunroof are numerically studied with varying body leakage. The effects of body leakage on ventilation and wind noise of a sunroof are examined, in particular. Furthermore, flow visualization, pressure and wind noise measured from the wind tunnel and road tests are presented. The results show that too small a body leakage results in poor ventilation performance and generates high wind noises around a sunroof. It is therefore very important to secure an adequate body leakage from the early design stage to achieve better performance of a sunroof as well as passengers' thermal comfort.
14
Koh, Frank C., Arthur T. Johnson, and Timothy E. Rehak. "Inward Leakage in Tight-Fitting PAPRs." Journal of Environmental and Public Health 2011 (2011): 1–8. http://dx.doi.org/10.1155/2011/473143.
Full textAbstract:
A combination of local flow measurement techniques and fog flow visualization was used to determine the inward leakage for two tight-fitting powered air-purifying respirators (PAPRs), the 3M Breathe-Easy PAPR and the SE 400 breathing demand PAPR. The PAPRs were mounted on a breathing machine head form, and flows were measured from the blower and into the breathing machine. Both respirators leaked a little at the beginning of inhalation, probably through their exhalation valves. In both cases, the leakage was not enough for fog to appear at the mouth of the head form.
15
Yamamoto, A. "Endwall Flow/Loss Mechanisms in a Linear Turbine Cascade With Blade Tip Clearance." Journal of Turbomachinery 111, no. 3 (July 1, 1989): 264–75. http://dx.doi.org/10.1115/1.3262265.
Full textAbstract:
This paper discusses the mechanisms of three-dimensional flows and of the associated losses occurring near the tip endwall region of a linear turbine cascade with tip clearance. The clearance gap sizes and the cascade incidences were chosen as the most important variables affecting the mechanisms. Flows close to the endwall and inside the clearance were surveyed in great detail using a micro five-hole pitot tube of 0.6 mm head size. The results gave very detailed information on the mechanisms, such as leakage flow vectors and pressure distributions throughout the clearance. Interaction of leakage flow with the endwall flow and their associated separation lines, effects of gap size and inlet flow angle on loss generation, and skewness of the three-dimensional endwall flows are also discussed.
16
Eryilmaz, Bora, and Bruce H. Wilson. "Combining Leakage and Orifice Flows in a Hydraulic Servovalve Model1." Journal of Dynamic Systems, Measurement, and Control 122, no. 3 (December 17, 1999): 576–79. http://dx.doi.org/10.1115/1.1286335.
Full textAbstract:
Experiments indicate that at small servovalve spool displacements, leakage flow between the valve spool and body dominates the orifice flow through the valve. In precision positioning applications, where the servovalve operates within the null region, this flow, if ignored, may severely degrade the performance of a conventional servohydraulic design. We have developed an improved servovalve model that combines both leakage and orifice flow. The model was developed by reviewing experimental leakage flow data and identifying a simple mathematical form that (1) made physical sense and (2) replicated experimental data. When combined with orifice relations, the model extends the accuracy and region of applicability of existing servovalve models. Furthermore, the combined model is easily parameterized using available manufacturer data. [S0022-0434(00)00403-2]
17
Patel, Hitesh H., and Vikas J. Lakhera. "Experimental Investigations on Leakages in Positive Displacement Machines." International Journal of Rotating Machinery 2021 (August 21, 2021): 1–16. http://dx.doi.org/10.1155/2021/6684329.
Full textAbstract:
The clearance gaps in positive displacement machines such as compressors, pumps, expanders, and turbines are critical for their performance and reliability. The leakage flow through these clearances influences the volumetric and adiabatic efficiencies of the machines. The extent of the leakage flow depends on the size and shape of clearance paths and pressure differences across these paths. Usually, the mass flow through the gaps is estimated using the isentropic nozzle equation with the flow coefficients applied to correct for the real flow conditions. However, the flow coefficients applied generally do not take into account the shape and size of these leakage paths. For that reason, a proper understanding of the relationship between flow coefficients and shape parameters is crucial for an accurate prediction of leakage flows. The present study investigates the influence of the various dimensionless parameters such as Reynolds number, Mach number, and pressure ratio on the flow coefficients for circular and rectangular clearance shapes. The flow coefficients are determined by comparing the experimental values obtained in an experimental test rig and the flow rates obtained from the isentropic nozzle equation. It is observed that in the case of circular clearances, the mean deviation of the experimental leakage results (in comparison to the analytical results using isotropic nozzle equations) is +9.1%, which is significantly lower than the mean deviation (+20.5%) in the case of rectangular clearance leakages. The study indicates that the isentropic nozzle equation method is more suitable for predicting the leakages through the circular clearances and needs modifications for consideration of the rectangular clearances. Using regression analysis, empirical correlations are developed to predict the flow coefficient in terms of Reynolds number, Mach number, pressure ratio, aspect ratio, and β ratio, which are found to match within ±6.4 percent of the numerical results for the rectangular clearance and within the range of -3.6 percent to +5.1 percent of the numerical result for the circular clearance. The empirical relationships presented in this study can be extended to evaluate the flow coefficients in a positive displacement machine.
18
Passmann, Maximilian, Stefan aus der Wiesche, and Franz Joos. "Focusing Schlieren Visualization of Transonic Turbine Tip-Leakage Flows." International Journal of Turbomachinery, Propulsion and Power 5, no. 1 (January 2, 2020): 1. http://dx.doi.org/10.3390/ijtpp5010001.
Full textAbstract:
This paper presents a focusing schlieren system designed for the investigation of transonic turbine tip-leakage flows. In the first part, the functional principle and the design of the system are presented. Major design considerations and necessary trade-offs are discussed. The key optical properties, e.g., depth of focus, are verified by means of a simple bench test. In the second part, results of an idealized tip-clearance model as well as linear cascade tests at engine representative Reynolds and Mach numbers are presented and discussed. The focusing schlieren system, designed for minimum depth of focus, has been found to be well suited for the investigation of three-dimensional transonic flow fields in turbomachinery applications. The schlieren images show the origin and growth of the tip-leakage vortex on the blade suction side. A complex shock system was observed in the tip region, and the tip-leakage vortex was found to interact with the suction side part of the trailing edge shock system. The results indicate that transonic vortex shedding is suppressed in the tip region at an exit Mach number around M 2 , i s = 0.8.
19
Wellborn, S. R., I. Tolchinsky, and T. H. Okiishi. "Modeling Shrouded Stator Cavity Flows in Axial-Flow Compressors." Journal of Turbomachinery 122, no. 1 (February 1, 1999): 55–61. http://dx.doi.org/10.1115/1.555427.
Full textAbstract:
Experiments and computational analyses were completed to understand the nature of shrouded stator cavity flows. From this understanding, a one-dimensional model of the flow through shrouded stator cavities was developed. This model estimates the leakage mass flow, temperature rise, and angular momentum increase through the cavity, given geometry parameters and the flow conditions at the interface between the cavity and primary flow path. This cavity model consists of two components, one that estimates the flow characteristics through the labyrinth seals and the other that predicts the transfer of momentum due to windage. A description of the one-dimensional model is given. The incorporation and use of the one-dimensional model in a multistage compressor primary flow analysis tool is described. The combination of this model and the primary flow solver was used to reliably simulate the significant impact on performance of the increase of hub seal leakage in a twelve-stage axial-flow compressor. Observed higher temperatures of the hub region fluid, different stage matching, and lower overall efficiencies and core flow than expected could be correctly linked to increased hub seal clearance with this new technique. The importance of including these leakage flows in compressor simulations is shown. [S0889-504X(00)00501-8]
20
Wallis, A. M., J. D. Denton, and A. A. J. Demargne. "The Control of Shroud Leakage Flows to Reduce Aerodynamic Losses in a Low Aspect Ratio, Shrouded Axial Flow Turbine." Journal of Turbomachinery 123, no. 2 (February 1, 2000): 334–41. http://dx.doi.org/10.1115/1.1354143.
Full textAbstract:
The losses generated by fluid leaking across the shrouds of turbine blade rows are known to form a significant proportion of the overall loss generated in low aspect ratio turbines. The use of shrouds to encase the tips of turbine blades has encouraged the development of many innovative sealing arrangements, all of which are intended to reduce the quantity of fluid (the leakage fraction) leaking across the shroud. Modern sealing arrangements have reduced leakage fractions considerably, meaning that further improvements can only be obtained by controlling the leakage flow in such a way so as to minimize the aerodynamic losses incurred by the extraction and re-injection of the leakage flow into the mainstream. There are few published experimental investigations on the interaction between mainstream and leakage flows to provide guidance on the best means of managing the leakage flows to do this. This paper describes the development and testing of a strategy to turn the fluid leaking over shrouded turbine rotor blade rows with the aim of reducing the aerodynamic losses associated with its re-injection into the mainstream flow. The intent was to extract work from the leakage flow in the process. A four stage research turbine was used to test in detail the sealing design resulting from this strategy. A reduction in brake efficiency of 3.5 percent was measured. Further investigation suggested that much of the increase in loss could be attributed to the presence of axial gaps upstream and downstream of the shroud cavity which facilitated the periodic ingress and egress of mainstream fluid into the shroud cavity under the influence of the rotor potential field. This process was exacerbated by reductions in the leakage fraction.
21
Rehder, Hans-Jürgen, and Axel Dannhauer. "Experimental Investigation of Turbine Leakage Flows on the Three-Dimensional Flow Field and Endwall Heat Transfer." Journal of Turbomachinery 129, no. 3 (July 20, 2006): 608–18. http://dx.doi.org/10.1115/1.2720484.
Full textAbstract:
Within a European research project, the tip endwall region of low pressure turbine guide vanes with leakage ejection was investigated at DLR in Göttingen. For this purpose a new cascade wind tunnel with three large profiles in the test section and a contoured endwall was designed and built, representing 50% height of a real low pressure turbine stator and simulating the casing flow field of shrouded vanes. The effect of tip leakage flow was simulated by blowing air through a small leakage gap in the endwall just upstream of the vane leading edges. Engine relevant turbulence intensities were adjusted by an active turbulence generator mounted in the test section inlet plane. The experiments were performed with tangential and perpendicular leakage ejection and varying leakage mass flow rates up to 2%. Aerodynamic and thermodynamic measurement techniques were employed. Pressure distribution measurements provided information about the endwall and vane surface pressure field and its variation with leakage flow. Additionally streamline patterns (local shear stress directions) on the walls were detected by oil flow visualization. Downstream traverses with five-hole pyramid type probes allow a survey of the secondary flow behavior in the cascade exit plane. The flow field in the near endwall area downstream of the leakage gap and around the vane leading edges was investigated using a 2D particle image velocimetry system. In order to determine endwall heat transfer distributions, the wall temperatures were measured by an infrared camera system, while heat fluxes at the surfaces were generated with electric operating heating foils. It turned out from the experiments that distinct changes in the secondary flow behavior and endwall heat transfer occur mainly when the leakage mass flow rate is increased from 1% to 2%. Leakage ejection perpendicular to the main flow direction amplifies the secondary flow, in particular the horseshoe vortex, whereas tangential leakage ejection causes a significant reduction of this vortex system. For high leakage mass flow rates the boundary layer flow at the endwall is strongly affected and seems to be highly turbulent, resulting in entirely different heat transfer distributions.
22
Sun, Shuaihui, Gursharanjit Singh, Ahmed Kovacevic, and Christoph Bruecker. "Experimental and Numerical Investigation of Tip Leakage Flows in a Roots Blower." Designs 4, no. 1 (February 6, 2020): 3. http://dx.doi.org/10.3390/designs4010003.
Full textAbstract:
Computational fluid dynamics (CFD) can help in understanding the nature of leakage flow phenomena inside the rotary positive displacement machines (PDMs). However, due to the lack of experimental results, the analysis of leakage flows in rotary PDMs by CFD has not yet been fully validated. Particle image velocimetry (PIV) tests with a microscopic lens and phase-lock were conducted to obtain the velocity field around the tip gap in an optical Roots blower. The three-dimensional unsteady CFD model of the Roots blower with the dynamic grids generated by Screw Compressor Rotor Grid Generation (SCORG) was established to predict the gap flow under the same operating conditions. The images obtained by the PIV tests were analyzed and some factors which compromise the quality of test results in the gap flow were identified, such as reflections and transparency of the window. The flow fields obtained by CFD have the same flow pattern and velocity magnitude as the experimental results in the majority of observed regions but overestimate the leakage flow velocity. The CFD results show a vortex induced by the leakage flow in the downstream region of the gap. The flow losses in the tip gap mainly happen at the entrance upstream of the gap. Finally, some suggestions for future work are discussed.
23
Saleh, Zainab, Eldad J. Avital, and Theodosios Korakianitis. "Effect of in-service burnout on the transonic tip leakage flows over flat tip model." Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy 234, no. 5 (September 30, 2019): 655–69. http://dx.doi.org/10.1177/0957650919877057.
Full textAbstract:
Un-shrouded turbine blades are more common than shrouded ones in gas turbine aero-engines since they reduce the weight and avoid the centrifugal loading caused by the blades’ shrouds. Despite these important advantages, the absence of the shroud leads to leakage flows across the tip gap and exposes the blade tip to high thermal load and thermal damages. In addition, the leakage flows can contribute up to 30% of the aerodynamic loss in a turbine stage. In this study, the effect of in-service burnout is explored using a fundamental flat tip model of a high-pressure gas turbine blade. This investigation is carried out both experimentally in a transonic wind tunnel and computationally using the Reynolds Averaged Navier-stokes approach at high-speed conditions. It is found that exposing the tip to the in-service burnout effect changes the leakage flow behaviour significantly when compared with the tip with sharp edges (i.e. the tip at the start of its operational life). Different flow acceleration, flow structure and shockwave pattern and interactions are captured for the round-edge flat tip (i.e. the tip exposed to in-service burnout). The effective tip gap is found to be much larger for the round-edge flat tip allowing more leakage flow into the tip gap which results into higher tip leakage losses in comparison to the sharp-edge tip. Experimental and computational flow visualisations, surface pressure distributions and discharge coefficient are given and analysed for several pressure ratios over the tip gap.
24
Shen, Simin, Zhongdong Qian, Bin Ji, and Ramesh K. Agarwal. "Numerical investigation of tip flow dynamics and main flow characteristics with varying tip clearance widths for an axial-flow pump." Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy 233, no. 4 (November 20, 2018): 476–88. http://dx.doi.org/10.1177/0957650918812541.
Full textAbstract:
The effects of varying tip clearance widths on tip flows dynamics and main flows characteristics for an axial-flow pump are studied employing computational fluid dynamics method. An analysis is presented for the distributions of turbulent kinetic energy, mean axial velocity, and mean vorticity magnitude at the specific flow rate of 0.7 Q BEP , focusing on flow patterns in the tip region with different tip clearance widths and associated flows. From the simulation results we find that the flow structure of tip vortex and its transportation strongly depend on the tip clearance width, especially for the extension of tip leakage vortex, appearance of induced vortex and the area of tip separation vortex. For a small clearance of 0.15 mm at 0.7 Q BEP, there is no tip separation vortex at the tip. When tip clearance width becomes larger, a tip separation vortex attaches more on the surface of blade tip as well as vortex intensity of tip flows increases. For tip clearances of 0.9 and 1.2 mm, there is a small part of induced vortex near the blade leading edge. Meanwhile, no induced vortex can be captured for tip clearances of 0.15 and 0.45 mm. The relative angle between the blade chord and tip leakage vortex trajectory reduces gradually when tip clearance width increases from 0.45 to 1.2 mm. Additionally, the radial position of tip leakage vortex core moves inwards as tip clearance width increases. Furthermore, a larger tip clearance width has greater effects on the main-stream characteristics especially near the shroud, which is due to more energy being exchanged between tip flows and main flows. At the flow rate 0.7 Q BEP, both the efficiency and head of the pump reduce with an increasing tip clearance because of greater energy loss.
25
Marschik, Christian, Wolfgang Roland, Marius Dörner, Georg Steinbichler, and Volker Schöppner. "Leakage-Flow Models for Screw Extruders." Polymers 13, no. 12 (June 9, 2021): 1919. http://dx.doi.org/10.3390/polym13121919.
Full textAbstract:
Many theoretical analyses of extrusion ignore the effect of the flight clearance when predicting the pumping capability of a screw. This might be reasonable for conventional extruder screws with “normal” clearances but leads to errors when more advanced screw designs are considered. We present new leakage-flow models that allow the effect of the flight clearance to be included in the analysis of melt-conveying zones. Rather than directly correcting the drag and pressure flows, we derived regression models to predict locally the shear-thinning flow through the flight clearance. Using a hybrid modeling approach that includes analytical, numerical, and data-based modeling techniques enabled us to construct fast and accurate regressions for calculating flow rate and dissipation rate in the leakage gap. Using the novel regression models in combination with network theory, the new approximations consider the effect of the flight clearance in the predictions of pumping capability, power consumption and temperature development without modifying the equations for the down-channel flow. Unlike other approaches, our method is not limited to any specific screw designs or processing conditions.
26
Piggush, J. D., and T. W. Simon. "Heat Transfer Measurements in a First-Stage Nozzle Cascade Having Endwall Contouring: Misalignment and Leakage Studies." Journal of Turbomachinery 129, no. 4 (August 11, 2006): 782–90. http://dx.doi.org/10.1115/1.2720506.
Full textAbstract:
This work supports new gas turbine designs for improved performance by evaluating endwall heat transfer rates in a cascade that is representative of a first-stage stator passage and incorporates endwall assembly features and leakage. Assembly features, such as gaps in the endwall and misalignment of those gaps, disrupt the endwall boundary layer, typically leading to enhanced heat transfer rates. Leakage flows through such gaps within the passage can also affect endwall boundary layers and may induce additional secondary flows and vortex structures in the passage near the endwall. The present paper documents leakage flow and misalignment effects on the endwall heat transfer coefficients within a passage which has one axially contoured and one straight endwall. In particular, features associated with the combustor-to-turbine transition piece and the assembly joint on the vane platform are addressed.
27
Hsu, Y., and C. E. Brennen. "Fluid Flow Equations for Rotordynamic Flows in Seals and Leakage Paths." Journal of Fluids Engineering 124, no. 1 (October 15, 2001): 176–81. http://dx.doi.org/10.1115/1.1436093.
Full textAbstract:
Fluid-induced rotordynamic forces produced by the fluid in an annular seal or in the leakage passage surrounding the shroud of a pump or turbine, are known to contribute substantially to the potential excitation forces acting on the rotor. The present research explores some of the important features of the equations governing bulk-flow models of these flows. This in turn suggests methods which might be used to solve these bulk-flow equations in circumstances where the linearized solutions may not be accurate. This paper presents a numerical method for these equations and discusses comparison of the computed results with experimental measurements for annular seals and pump leakage paths.
28
Joshi, Ashish M., David I. Blekhman, James D. Felske, John A. Lordi, and Joseph C. Mollendorf. "Clearance Analysis and Leakage Flow CFD Model of a Two-Lobe Multi-Recompression Heater." International Journal of Rotating Machinery 2006 (2006): 1–10. http://dx.doi.org/10.1155/ijrm/2006/79084.
Full textAbstract:
This paper reports the results of a study on multi-recompression heating. This process employs a Roots-type mechanism to heat gases to very high temperatures by compressive gas heating. A CFD model predicting the leakage flows in the machine was developed, and an excellent comparison with experimental data taken on a two-lobe Roots blower was obtained. A “clearance analysis” was performed to show that the clearance between the impellers remains constant for 96% of the angles of rotation. Assuming a quasi-steady state, the CFD simulation was performed for a single angle of rotation. A three-dimensional analysis showed that the flow field is identical along the rotor length, except for the leakage through the end plates. Hence, the model was further simplified to a two-dimensional analysis. This research may provide guidance in predicting the leakage flows in other blowers of the same kind with a different geometry.
29
Pegler, Samuel S., Herbert E. Huppert, and Jerome A. Neufeld. "Fluid migration between confined aquifers." Journal of Fluid Mechanics 757 (September 19, 2014): 330–53. http://dx.doi.org/10.1017/jfm.2014.469.
Full textAbstract:
AbstractWe study the two-dimensional flow and leakage of buoyant fluid injected at a constant volumetric rate into a fluid-saturated porous medium confined vertically by horizontal boundaries. The upper boundary contains a localized vertical fracture that allows fluid to leak into an open or partially confined porous layer above. The rate of leakage is modelled as proportional to the combined action of the gravitational hydrostatic head of the current below the fracture and the background pressure introduced by the injection. After the injected current reaches the fracture, leakage is initially controlled kinematically by the rate at which injected fluid flows towards the fracture. Once the rate at which buoyant fluid flows towards the fracture exceeds a critical value, the current overshoots the fracture and leakage switches to being controlled dynamically by the pressure drop across the fracture. Two long-term regimes of flow can emerge. In one, the current approaches a steady height above the lower boundary and essentially all fluid injected into the medium leaks at long times. In the other, the current accumulates to fill the entire depth of the medium below the fracture. Only a fraction of the injected fluid then leaks at long times, implying significantly greater long-term storage than has been proposed from studies of leakage from unconfined media. An understanding of the flow regimes is obtained using numerical solutions and analysis of long-term similarity solutions. The implications of our results to the geological storage of carbon dioxide is discussed.
30
Guinzburg, A., C. E. Brennen, A. J. Acosta, and T. K. Caughey. "Experimental Results for the Rotordynamic Characteristics of Leakage Flows in Centrifugal Pumps." Journal of Fluids Engineering 116, no. 1 (March 1, 1994): 110–15. http://dx.doi.org/10.1115/1.2910217.
Full textAbstract:
In recent years, increasing attention has been given to fluid-structure interaction problems in turbomachines. The present research focuses on just one such fluid-structure interaction problem, namely, the role played by fluid forces in determining the rotordynamic stability and characteristics of a centrifugal pump. The emphasis of this study is to investigate the contributions to the rotordynamic forces from the discharge-to-suction leakage flows between the front shroud of the rotating impeller and the stationary pump casing. An experiment was designed to measure the rotordynamic shroud forces due to simulated leakage flows for different parameters such as flow rate, shroud clearance, face-seal clearance and eccentricity. The data demonstrate substantial rotordynamic effects and a destabilizing tangential force for small positive whirl frequency ratios; this force decreased with increasing flow rate. The rotordynamic forces appear to be inversely proportional to the clearance and change significantly with the flow rate. Two sets of data taken at different eccentricities yielded quite similar nondimensional rotordynamic forces indicating that the experiments lie within the linear regime of eccentricity.
31
Zeinali, Marhamat, Sarallah Abbasi, and Abolfazl Hajizadeh Aghdam. "Commencement and Development Processes of Flow Unsteadiness at Tip Clearance Region of a Low Speed Axial Compressor Rotor Blade Row." Periodica Polytechnica Mechanical Engineering 61, no. 4 (September 19, 2017): 288. http://dx.doi.org/10.3311/ppme.11113.
Full textAbstract:
Commencement and development processes of unsteadiness, caused by blade row tip leakage flow in a low speed axial compressor, are investigated and results are presented in this paper. Analyses are based on results obtained through numerical simulation of unsteady three dimensional viscous flows. Discretization of the Navier-Stokes’s equations has been carried out based on upwind second-order scheme and k-ω-SST turbulence modeling was used for estimation of eddy viscosity.Three different circumstances, including design point and two near stall conditions are considered for investigation and discussion. Tip leakage flow frequency spectrums were examined through surveying instantaneous static pressure signals imposed on the blades surfaces. Focusing on time dependent flow structure results signified existence of some pressure peaks at near stall conditions. These regions, which are created as a result of interaction between main inflow and tip leakage flow, lead to occurrence of self-induced unsteadiness. However, at design condition, flow is more affected by the main inflow instead of the tip leakage flow. By occurrence of self-induced unsteadiness, which occurs at near stall condition, tip leakage vortex flow starts to fluctuate at a frequency about the blade passing frequency. Further decrease in the flow rate up to a specified value showed no significant variations in the leakage flow frequency, but, on the other hand, magnified amplitudes of this unsteadiness.
32
Fürst, Jiří. "Numerical Simulation of Flows through Labyrinth Seals." Applied Mechanics and Materials 821 (January 2016): 16–22. http://dx.doi.org/10.4028/www.scientific.net/amm.821.16.
Full textAbstract:
A numerical code for calculation of leakage flowand rotordynamic coefficients of labyrinth seals has beendeveloped. The code is based on the solution of Reynolds-averagedNavier-Stokes equations combined with a two-equation turbulencemodel. The numerical solution is achieved with finite volume methodand the rotordynamic coefficients are evaluated from severalsimulations with different rotor precessions. The solution iscompared to single control volume based bulk flow method[Williams, 1998] and to the experimental results for look-throughlabyrinth seal [Schettel, 2004].
33
De Pontieu, Bart, Robert Erdélyi, and Stewart P. James. "Solar chromospheric spicules from the leakage of photospheric oscillations and flows." Nature 430, no. 6999 (July 2004): 536–39. http://dx.doi.org/10.1038/nature02749.
Full text
34
Adams, Nathan G., and H. Kent Hepworth. "Flow visualization study of tip leakage flows across cantilevered stator blades." Journal of Propulsion and Power 4, no. 2 (March 1988): 144–51. http://dx.doi.org/10.2514/3.23042.
Full text
35
Zhao, Yu, Yutong Jiang, Xiaolong Cao, and Guoyu Wang. "Study on tip leakage vortex cavitating flows using a visualization method." Modern Physics Letters B 32, no. 01 (January 10, 2018): 1850003. http://dx.doi.org/10.1142/s0217984918500033.
Full textAbstract:
Experimental investigations of unsteady cavitating flows in a hydrofoil tip leakage region with different gap sizes are conducted to highlight the development of gap cavitation. The experiments were taken in a closed cavitation tunnel, during which high-speed camera had been used to capture the cavitation patterns. A new visualization method based on image processing was developed to capture time-dependent cavitation patterns. The results show that the visualization method can effectively capture the cavitation patterns in the tip region, including both the attached cavity in the gap and the tip leakage vortex (TLV) cavity near the trailing edge. Moreover, with the decrease of cavitation number, the TLV cavity develops from a rapid onset-growth-collapse process to a continuous process, and extends both upstream and downstream. The attached cavity in the gap develops gradually stretching beyond the gap and combines with the vortex cavity to form the triangle cavitating region. Furthermore, the influences of gap size on the cavitation are also discussed. The gap size has a great influence on the loss across the gap, and hence the locations of the inception attached cavity. Besides, inception locations and extending direction of the TLV cavity with different gap sizes also differ. The TLV in the case with [Formula: see text] = 0.061 is more likely to be jet-like compared with that in the case with [Formula: see text] = 0.024, and the gap size has a great influence on the TLV strength.
36
KABURAKI, Hideo, and Takakazu TAKIZUKA. "Leakage Flows in High-Temperature Gas-Cooled Reactor Graphite Fuel Elements." Journal of Nuclear Science and Technology 22, no. 5 (May 1985): 387–97. http://dx.doi.org/10.1080/18811248.1985.9735672.
Full text
37
Cao, Zhiyuan, Cheng Song, Xiang Zhang, Xi Gao, and Bo Liu. "Blade Lean and Tip Leakage Flows in Highly Loaded Compressor Cascades." Journal of Thermal Science 30, no. 4 (July 2021): 1388–405. http://dx.doi.org/10.1007/s11630-021-1486-4.
Full text
38
Feng, Pengbin, Jianfeng Ma, and Cong Sun. "Selecting Critical Data Flows in Android Applications for Abnormal Behavior Detection." Mobile Information Systems 2017 (2017): 1–16. http://dx.doi.org/10.1155/2017/7397812.
Full textAbstract:
Nowadays, mobile devices are widely used to store and process user privacy and confidential data. With the popularity of Android platform, the cases of attacks against users’ privacy-sensitive data within Android applications are on the rise. Researchers have developed sophisticated static and dynamic analysis tools to detect information leakage. These methods cannot distinguish legitimate usage of sensitive data in benign apps from the intentional sensitive data leakages in malicious apps. Recently, malicious apps have been found to treat sensitive data differently from benign apps. These differences can be used to flag malicious apps based on their abnormal data flows. In this paper, we further find that some sensitive data flows show great difference between benign apps and malware. We can use these differences to select critical data flows. These critical flows can guide the identification of malware based on the abnormal usage of sensitive data. We present SCDFLOW, a tool that automatically selects critical data flows within Android applications and takes these critical flows as feature for abnormal behavior detection. Compared with MUDFLOW, SCDFLOW increases the true positive rate of malware detection by 5.73%~9.07% on different datasets and causes an ignorable effect on memory consumption.
39
Yang, Xu, Zong Chang Qu, and Yu Yuan Wu. "Leakage Analysis of a Synchronal Rotary Multiphase Pump." Advanced Materials Research 562-564 (August 2012): 635–38. http://dx.doi.org/10.4028/www.scientific.net/amr.562-564.635.
Full textAbstract:
A novel positive-displacement multiphase pump named synchronal rotary multiphase pump (SRMP) was introduced. The two-phase leakage flows through the various leakage clearances in the SRMP were theoretically analyzed and formulated. Calculations on the leakage loss of a SRMP prototype were performed. The results show that the leakage loss is mainly produced by the leakage through the radical clearance between the rotor and cylinder. The SRMP presents a lower volumetric efficiency at a higher pressure difference. The leakage loss increases rapidly with the increase of the gas volume fraction of the two-phase working fluids.
40
Pouagare, M., and R. A. Delaney. "Study of Three-Dimensional Viscous Flows in an Axial Compressor Cascade Including Tip Leakage Effects Using a SIMPLE-Based Algorithm." Journal of Turbomachinery 108, no. 1 (July 1, 1986): 51–58. http://dx.doi.org/10.1115/1.3262024.
Full textAbstract:
A multisweep space-marching solver based on a modified version of the SIMPLE algorithm was employed to study the three-dimensional flow field through a linear cascade. Three cases were tested: one with moderate loading, one with high loading, and one with high loading and tip clearance. The results of the numerical simulation were compared with available experimental measurements, and the agreement between the two was found satisfactory. The numerical simulation provided insight into several important endwall flow phenomena such as the interaction between the leakage and passage vortices, the interaction between the leakage vortex and the wake, the effect of leakage flow and loading on losses and secondary kinetic energy, the suction side corner separation, and the blowing of this separation by the leakage flow.
41
Goto, A. "The Effect of Tip Leakage Flow on Part-Load Performance of a Mixed-Flow Pump Impeller." Journal of Turbomachinery 114, no. 2 (April 1, 1992): 383–91. http://dx.doi.org/10.1115/1.2929155.
Full textAbstract:
The flow phenomena around the positive slope region of the head-flow characteristic were investigated experimentally on a mixed-flow pump impeller at various tip clearances for both shrouded and unshrouded cases. A positively sloped head-flow characteristic (abrupt decrease in pressure head) was caused by the onset of extensive flow separation in the impeller at the casing-suction surface corner. The corner separation in unshrouded cases appeared at a much lower flow rate than the shrouded case due to the favorable effect of the tip leakage flow, which displaced the wake region away from the corner. The interaction between the tip leakage flows and secondary flows and the formation of the wake regions in shrouded and unshrouded cases were explained based on experimental observation and computations by the Dawes three-dimensional Navier–Stokes code. In the shrouded case, the flow rate at which an abrupt decrease in pressure head appeared was lowered substantially by introducing a leakage flow through a slit made between the shroud and the blade tip. Inlet recirculation was triggered by the corner separation and developed more gradually for larger tip clearances. Both the increased loss, due to the extensive flow separation, and the decreased Euler’s head, due to the abrupt change in flow pattern caused by the inlet recirculation, were responsible for the generation of positively sloped head-flow characteristic in the unshrouded case when the tip clearance was small, while the increased loss was the primary factor in the shrouded case.
42
Gier, Jochen, Bertram Stubert, Bernard Brouillet, and Laurent de Vito. "Interaction of Shroud Leakage Flow and Main Flow in a Three-Stage LP Turbine." Journal of Turbomachinery 127, no. 4 (March 1, 2003): 649–58. http://dx.doi.org/10.1115/1.2006667.
Full textAbstract:
Endwall losses significantly contribute to the overall losses in modern turbomachinery, especially when aerodynamic airfoil load and pressure ratios are increased. In turbines with shrouded airfoils a large portion of these losses are generated by the leakage flow across the shroud clearance. Generally the related losses can be grouped into losses of the leakage flow itself and losses caused by the interaction with the main flow in subsequent airfoil rows. In order to reduce the impact of the leakage flow and shroud design related losses a thorough understanding of the leakage losses and especially of the losses connected to enhancing secondary flows and other main flow interactions has to be understood. Therefore, a three stage LP turbine typical for jet engines is being investigated. For the three-stage test turbine 3D Navier-Stokes computations are performed simulating the turbine including the entire shroud cavity geometry in comparison with computations in the ideal flow path. Numerical results compare favorably against measurements carried out at the high altitude test facility at Stuttgart University. The differences of the simulations with and without shroud cavities are analyzed for several points of operation and a very detailed quantitative loss breakdown is presented.
43
Lu, Hanan, Qiushi Li, Tianyu Pan, and Ramesh Agarwal. "Analysis and application of shroud wall optimization to an axial compressor with upstream boundary layer to improve aerodynamic performance." International Journal of Numerical Methods for Heat & Fluid Flow 29, no. 11 (November 4, 2019): 4237–61. http://dx.doi.org/10.1108/hff-01-2019-0071.
Full textAbstract:
PurposeFor an axial-flow compressor rotor, the upstream inflow conditions will vary as the aircraft faces harsh flight conditions (such as taking off, landing or maneuvering) or the whole compressor operates at off-design conditions. With the increase of upstream boundary layer thickness, the rotor blade tip will be loaded and the increased blade load will deteriorate the shock/boundary layer interaction and tip leakage flows, resulting in high aerodynamic losses in the tip region. The purpose of this paper is to achieve a better flow control for tip secondary flows and provide a probable design strategy for high-load compressors to tolerate complex upstream inflow conditions.Design/methodology/approachThis paper presents an analysis and application of shroud wall optimization to a typical transonic axial-flow compressor rotor by considering the inlet boundary layer (IBL). The design variables are selected to shape the shroud wall profile at the tip region with the purpose of controlling the tip leakage loss and the shock/boundary layer interaction loss. The objectives are to improve the compressor efficiency at the inlet-boundary-layer condition while keeping its aerodynamic performance at the uniform condition.FindingsAfter the optimization of shroud wall contour, aerodynamic benefits are achieved mainly on two aspects. On the one hand, the shroud wall optimization has reduced the intensity of the tip leakage flow and the interaction between the leakage and main flows, thereby decreasing the leakage loss. On the other hand, the optimized shroud design changes the shock structure and redistributes the shock intensity in the spanwise direction, especially weakening the shock near the tip. In this situation, the shock/boundary layer interaction and the associated flow separations and wakes are also eliminated. On the whole, at the inlet-boundary-layer condition, the compressor with optimized shroud design has achieved a 0.8 per cent improvement of peak efficiency over that with baseline shroud design without sacrificing the total pressure ratio. Moreover, the re-designed compressor also maintains the aerodynamic performance at the uniform condition. The results indicate that the shroud wall profile has significant influences on the rotor tip losses and could be properly designed to enhance the compressor aerodynamic performance against the negative impacts of the IBL.Originality/valueThe originality of this paper lies in developing a shroud wall contour optimization design strategy to control the tip leakage loss and the shock/boundary layer interaction loss in a transonic compressor rotor. The obtained results could be beneficial for transonic compressors to tolerate the complex upstream inflow conditions.
44
Meng, Fusheng, Qun Zheng, Jie Gao, and Weiliang Fu. "Effect of Tip Clearance on Flow Field and Heat Transfer Characteristics in a Large Meridional Expansion Turbine." Energies 12, no. 1 (January 4, 2019): 162. http://dx.doi.org/10.3390/en12010162.
Full textAbstract:
The large meridional expansion turbine stator leads to complex secondary flows and heat transfer characteristics in the blade endwall region, while the upstream tip clearance leakage flow of the rotor makes it more complex in flow and heat transfer. The influence of the upstream rotor tip clearance on the large meridian expansion stator is worth studying. The flow and heat transfer characteristics of the downstream large meridional expansion turbine stator were studied by comparing the tip leakage flow of 1.5-stage shrouded and unshrouded turbines using a three-dimensional Reynolds-Averaged Navier-Stokes (RANS) solver for viscous turbulent flows. Validation studies were performed to investigate the aerodynamics and heat transfer prediction ability of the shear stress transport (SST) turbulence model. The influence of different tip clearances of the rotor including unshrouded blade heights of 0%, 1% and 5% and a 1% shrouded blade height were investigated through numerical simulation. The results showed that the upper passage vortex separation was more serious and the separation, and attachment point of horseshoe vortex in the pressure side were significantly more advanced than that of non-expansion turbines. The tip leakage vortex obviously increased the negative incidence angle at the downstream inlet. Furthermore, the strength of the high heat transfer zone on the suction surface of the downstream stator was significantly increased, while that of the shrouded rotor decreased.
45
Lee, Seong Jun. "A Simultaneous Model for Simulating the Propagation of Hydraulic Head in Aquifers with Leakage Pathways." Environment and Natural Resources Research 6, no. 2 (May 4, 2016): 65. http://dx.doi.org/10.5539/enrr.v6n2p65.
Full textAbstract:
A three-dimensional simultaneous solution model was developed for analysis of variable transient flows, specifically leakage associated with arbitrary groundwater aquifers. The model simultaneously calculates leakage rates using the hydraulic gradients between coupled leakage points at two leaky aquifers and evaluates the propagation of hydraulic heads in multiple aquifers resulting from that leakage. Important considerations for leakage simulation are variant leakage rates with time and leakage starting time. Two types of leakage pathways are specified in terms of the generated time, including (1) pre-existing leakage pathways and (2) abruptly-induced leakage pathways at specific times. The governing equation with a leakage term is composed of three finite difference equations, and its form depends on whether leakage pathways pre-exist or are induced at specified times according to known or assumed aquifer histories. The developed numerical code was validated by comparison with the results of the TOUGH2/EOS1 program for a three-dimensional conceptual domain.
46
Gerolymos, G. A., and I. Vallet. "Tip-Clearance and Secondary Flows in a Transonic Compressor Rotor." Journal of Turbomachinery 121, no. 4 (October 1, 1999): 751–62. http://dx.doi.org/10.1115/1.2836729.
Full textAbstract:
The purpose of this paper is to investigate tip-clearance and secondary flows numerically in a transonic compressor rotor. The computational method used is based on the numerical integration of the Favre-Reynolds-averaged three-dimensional compressible Navier–Stokes equations, using the Launder–Sharma near-wall k–ε turbulence closure. In order to describe the flowfield through the tip and its interaction with the main flow accurately, a fine O-grid is used to discretize the tip-clearance gap. A patched O-grid is used to discretize locally the mixing-layer region created between the jetlike flow through the gap and the main flow. An H–O–H grid is used for the computation of the main flow. In order to substantiate the validity of the results, comparisons with experimental measurements are presented for the NASA_37 rotor near peak efficiency using three grids (of 106, 2 X 106, and 3 X 106 points, with 21, 31, and 41 radial stations within the gap, respectively). The Launder–Sharma k–ε model underestimates the hub corner stall present in this configuration. The computational results are then used to analyze the interblade-passage secondary flows, the flow within the tip-clearance gap, and the mixing downstream of the rotor. The computational results indicate the presence of an important leakage-interaction region where the leakage-vortex after crossing the passage shock-wave mixes with the pressure-side secondary flows. A second trailing-edge tip vortex is also clearly visible.
47
Zhu, Jintuo, Xinjian He, Steve Guffey, Liang Wang, Haifeng Wang, and Jianwei Cheng. "Performance Comparison of N95 and P100 Filtering Facepiece Respirators with Presence of Artificial Leakage." Annals of Work Exposures and Health 64, no. 2 (November 30, 2019): 202–16. http://dx.doi.org/10.1093/annweh/wxz086.
Full textAbstract:
Abstract Objectives National Institute for Occupational Safety and Health–approved P100 filtering facepiece respirators (FFRs) have a higher filter efficiency compared to the N95 filters. However, the former typically produce higher flow resistance (Rf). Consequently, when faceseal leakage is present, the proportion of leakage airflow for P100 FFRs may exceed that of N95s, resulting in a higher total inward leakage (TIL) of the P100. Methods In this manikin-based study, the performance of two pairs of N95 and P100 FFRs (N95-A versus P100-A; N95-B versus P100-B) were compared under five sealing conditions (fully sealed and partially sealed with one, two, or three leaks of 0.8-mm, and one 2-mm leak). Sodium chloride particles (CMD ~45 nm) were used as the challenge aerosol. Respirators were tested under three constant flows (15, 50, and 85 L/min) and three cyclic flows (mean inspiratory flow = 15, 50, and 85 L/min). Both filter penetration (Pfilter) and TIL were determined. The Rf under constant flows was recorded. Based on Pfilter, TIL, and Rf, the quality factor (qf) was calculated to compare the overall performance of N95 and P100 FFRs. Results For a fully sealed condition, the Pfilter was much lower for the P100 FFRs than for the N95 FFRs. When small leaks were inserted (0.8-mm and 2 × 0.8-mm), the TIL was higher for the P100 FFRs than for the N95 FFRs under the lowest tested flow (15 L/min), while for greater leaks (3 × 0.8-mm and 2-mm), the TIL of the P100 FFRs was always higher regardless of the flow. The Rf of P100 FFRs was measured twice as high as the N95. The qf values were also found higher for the N95 FFRs than for the P100 FFRs regardless of leak size and breathing flow. Conclusions With the presence of artificial leakage, a P100 FFR with high-flow-resistance may not be as protective as a low-flow-resistance N95 FFR. This finding suggests that future efforts should be directed to reducing the breathing resistance when designing P100 FFRs.
48
Sha, Zhao Jun, Rong Xie, Xiao Fang Wang, Xu Dong Ding, and Yong Feng Sui. "Numerical Investigation on the Flow in Tip Clearance of the Last Three Stages of Industrial Steam Turbine." Applied Mechanics and Materials 721 (December 2014): 78–81. http://dx.doi.org/10.4028/www.scientific.net/amm.721.78.
Full textAbstract:
Numerical investigation was conducted on the full-three-dimensional flow in the last three stages of steam turbine using by the commercial computational flow dynamics software CFX. And the equilibrium condensation model was adopted to describe the wet steam two phase flows. This article analyzes the internal flow of the turbine with tip clearance and the structure of the leakage flow.
49
Janse van Rensburg, J. J., and M. Kleingeld. "Investigating leakage and bypass flows in an HTR using a CFD methodology." Nuclear Engineering and Design 241, no. 12 (December 2011): 4960–71. http://dx.doi.org/10.1016/j.nucengdes.2011.08.073.
Full text
50
van Zyl, J. E., A. O. Lambert, and R. Collins. "Realistic Modeling of Leakage and Intrusion Flows through Leak Openings in Pipes." Journal of Hydraulic Engineering 143, no. 9 (September 2017): 04017030. http://dx.doi.org/10.1061/(asce)hy.1943-7900.0001346.
Full text