The flow dynamics of the garden-hose instability

We present fully resolved simulations of the flow–structure interaction in a flexible pipe conveying incompressible fluid. It is shown that the Reynolds number plays a significant role in the onset of flutter for a fluid-conveying pipe modelled through the classic garden-hose problem. We investigate the complex interaction between structural and internal flow dynamics and obtain a phase diagram of the transition between states as function of three non-dimensional quantities: the fluid-tension parameter, the dimensionless fluid velocity and the Reynolds number. We find that the flow patterns inside the pipe strongly affect the type of induced motion. For unsteady flow, if there is symmetry along a direction, this leads to in-plane motion whereas breaking of the flow symmetry results in both in-plane and out-of-plane motions. Hence, above a critical Reynolds number, complex flow patterns result for the vibrating pipe as there is continuous generation of new vorticity due to the pipe wall acceleration, which is subsequently shed in the confined space of the interior of the pipe.

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Computational Study of Gas Turbine Blade Cooling Channel

2010 14th International Heat Transfer Conference, Volume 5 ◽

10.1115/ihtc14-22920 ◽

2010 ◽

Cited By ~ 3

Author(s):

R. S. Amano ◽

Krishna Guntur ◽

Jose Martinez Lucci

Keyword(s):

Heat Transfer ◽

Reynolds Number ◽

Gas Turbine ◽

Turbulence Models ◽

Flow Patterns ◽

Higher Order ◽

Secondary Flows ◽

Complex Flow ◽

Cooling Performance ◽

Cooling Channels

It has been a common practice to use cooling passages in gas turbine blade in order to keep the blade temperatures within the operating range. Insufficiently cooled blades are subject to oxidation, to cause creep rupture, and even to cause melting of the material. To design better cooling passages, better understanding of the flow patterns within the complicated flow channels is essential. The interactions between secondary flows and separation lead to very complex flow patterns. To accurately simulate these flows and heat transfer, both refined turbulence models and higher-order numerical schemes are indispensable for turbine designers to improve the cooling performance. Power output and the efficiency of turbine are completely related to gas firing temperature from chamber. The increment of gas firing temperature is limited by the blade material properties. Advancements in the cooling technology resulted in high firing temperatures with acceptable material temperatures. To better design the cooling channels and to improve the heat transfer, many researchers are studying the flow patterns inside the cooling channels both experimentally and computationally. In this paper, the authors present the performance of three turbulence models using TEACH software code in comparison with the experimental values. To test the performance, a square duct with rectangular ribs oriented at 90° and 45° degree and placed at regular intervals. The channel also has bleed holes. The normalized Nusselt number obtained from simulation are validated with that of experiment. The Reynolds number is set at 10,000 for both the simulation and experiment. The interactions between secondary flows and separation lead to very complex flow patterns. To accurately simulate these flows and heat transfer, both refined turbulence models and higher-order numerical schemes are indispensable for turbine designers to improve the cooling performance. The three-dimensional turbulent flows and heat transfer are numerically studied by using several different turbulence models, such as non-linear low-Reynolds number k-omega and Reynolds Stress (RSM) models. In k-omega model the cubic terms are included to represent the effects of extra strain-rates such as streamline curvature and three-dimensionality on both turbulence normal and shear stresses. The finite volume difference method incorporated with the higher-order bounded interpolation scheme has been employed in the present study. The outcome of this study will help determine the best suitable turbulence model for future studies.

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Effect of Reynolds Number on Five-Hole Probe Performance: Experimental Study of the Open-Access Oxford Probe

Journal of Turbomachinery ◽

10.1115/1.4050597 ◽

2021 ◽

pp. 1-35

Author(s):

Maximilian Passmann ◽

Stefan aus der Wiesche ◽

Thomas Povey ◽

Detlef Bergmann

Keyword(s):

Reynolds Number ◽

Open Access ◽

Flow Dynamics ◽

Probe Design ◽

Data Sets ◽

Complex Flow ◽

Wide Range ◽

Oil Flow ◽

Flow Visualizations ◽

Underlying Mechanisms

Abstract There is relatively little literature concerning the effect of Reynolds number on multihole aerodynamic probe performance. In particular, there is almost no discussion in the literature regarding the underlying mechanisms of Reynolds number (Re) sensitivity for such probes. In order to close this gap, detailed investigations of the effect of Re on a five-hole probe have been performed using both PIV techniques and oil flow visualizations. Wind- and water-tunnels were used to cover a wide range of Re. The open-access Oxford Probe was used for these studies because of the readily available data-sets and processing routines, and to allow future comparisons by other authors. Complex flow dynamics including flow separation and re-attachment were identified, which cause Re-sensitivity of the calibration map at low Re even for low yaw or pitch angles. By comparing calibration maps across a wide range of Re, we demonstrate that the Oxford Probe can be employed without much loss of accuracy at lower Re levels than initially (conservatively) suggested, and quantify the errors in the extreme low-Re regime. Overall we demonstrate the robustness of the Oxford Probe concept across a wide range of Re conditions, we more clearly defined the low-Re limit for the probe design and quantify errors below this limit, and we illustrate the fundamental mechanisms for Re-sensitivity of multi-hole probes.

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Time-resolved flow dynamics and Reynolds number effects at a wall–cylinder junction

Journal of Fluid Mechanics ◽

10.1017/jfm.2015.341 ◽

2015 ◽

Vol 776 ◽

pp. 475-511 ◽

Cited By ~ 27

Author(s):

Nikolaos Apsilidis ◽

Panayiotis Diplas ◽

Clinton L. Dancey ◽

Polydefkis Bouratsis

Keyword(s):

Reynolds Number ◽

Turbulent Flows ◽

Large Scale ◽

Adverse Pressure Gradient ◽

Horseshoe Vortex ◽

Flow Patterns ◽

Flow Dynamics ◽

Flow Topology ◽

Time Resolved ◽

Reynolds Number Effects

This study investigated the physics of separated turbulent flows near the vertical intersection of a flat wall with a cylindrical obstacle. The geometry imposes an adverse pressure gradient on the incoming boundary layer. As a result, flow separates from the wall and reorganizes to a system of characteristic flow patterns known as the horseshoe vortex. We studied the time-averaged and instantaneous behaviour of the turbulent horseshoe vortex using planar time-resolved particle image velocimetry (TRPIV). In particular, we focused on the effect of Reynolds number based on the diameter of the obstacle and the bulk approach velocity, $\mathit{Re}_{D}$. Experiments were carried out at $\mathit{Re}_{D}$: $2.9\times 10^{4}$, $4.7\times 10^{4}$ and $12.3\times 10^{4}$. Data analysis emphasized time-averaged and turbulence quantities, time-resolved flow dynamics and the statistics of coherent flow patterns. It is demonstrated that two large-scale vortical structures dominate the junction flow topology in a time-averaged sense. The number of additional vortices with intermittent presence does not vary substantially with $\mathit{Re}_{D}$. In addition, the increase of turbulence kinetic energy (TKE), momentum and vorticity content of the flow at higher $\mathit{Re}_{D}$ is documented. The distinctive behaviour of the primary horseshoe vortex for the $\mathit{Re}_{D}=12.3\times 10^{4}$ case is manifested by episodes of rapid advection of the vortex to the upstream, higher spatio-temporal variability of its trajectory, and violent eruptions of near-wall fluid. Differences between this experimental run and those at lower Reynolds numbers were also identified with respect to the spatial extents of the bimodal behaviour of the horseshoe vortex, which is a well-known characteristic of turbulent junction flows. Our findings suggest a modified mechanism for the aperiodic switching between the dominant flow modes. Without disregarding the limitations of this work, we argue that Reynolds number effects need to be considered in any effort to control the dynamics of junction flows characterized by the same (or reasonably similar) configurations.

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Numerical Evaluation of 2D and 3D Steady and Unsteady Flows of a Pair of Opposing Confined Impinging Air Jets

Volume 2: Theory and Fundamental Research; Aerospace Heat Transfer; Gas Turbine Heat Transfer; Computational Heat Transfer ◽

10.1115/ht2009-88303 ◽

2009 ◽

Author(s):

Victor Chiriac ◽

Jorge L. Rosales

Keyword(s):

Heat Transfer ◽

Reynolds Number ◽

Unsteady Flow ◽

Flow Patterns ◽

Temperature Fields ◽

Transfer Coefficients ◽

Complex Flow ◽

Air Jets ◽

2D And 3D ◽

The Impact

The steady and unsteady laminar flow and heat transfer characteristics for a pair of opposing confined impinging slot jets in 2D and 3D were evaluated numerically at two Reynolds numbers. The present study continues the authors’ earlier work [1] and identifies the main similarities and differences arising from the expansion to the third dimension. At lower Reynolds number jet (Re = 300), the flow interaction produces a symmetric, steady flow hydrodynamic pattern with the jets being deflected laterally for the 2D flow. At Re = 300, the 3D slot jet produces almost the same values as the 2D case, yet the flow is slightly asymmetrical and unsteady. However, by further increasing the Reynolds number to 750, a complex and highly unsteady flow develops for both 2D and 3D simulations. The symmetry of both the 2D and 3D flows is disrupted and the resulting complex flow patterns reveal the vortex pairing effects, leading to the jet “buckling and sweeping” motion, enabling the enhanced local heat transfer. The convective heat transfer coefficients and the unsteady flow development between the jets are thoroughly investigated, with the flow unsteadiness also characterized by analyzing the stagnation point displacement on the channel walls. The comparison between the 2D and 3D flow patterns indicate that the 3D opposite jets enhance the unsteady effects compared to the 2D unsteady opposite jets. The complex vortex patterns resulting from the unsteady jets interaction, as well as the velocity, vorticity and temperature fields for both 2D and 3D cases are thoroughly evaluated. The comparison between the 2D and 3D impinging air jets is documented and the impact on chip/microelectronics cooling is highlighted.

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Effect of Reynolds Number on Five-Hole Probe Performance: Experimental Study of the Open-Access Oxford Probe

Volume 5: Controls, Diagnostics, and Instrumentation; Cycle Innovations; Cycle Innovations: Energy Storage ◽

10.1115/gt2020-16074 ◽

2020 ◽

Author(s):

Maximilian Passmann ◽

Stefan aus der Wiesche ◽

Thomas Povey ◽

Detlef Bergmann

Keyword(s):

Reynolds Number ◽

Open Access ◽

Flow Dynamics ◽

Probe Design ◽

Data Sets ◽

Complex Flow ◽

Wide Range ◽

Oil Flow ◽

Flow Visualizations ◽

Underlying Mechanisms

Abstract There is relatively little literature concerning the effect of Reynolds number on multi-hole aerodynamic probe performance. In particular, there is almost no discussion in the literature of the underlying mechanisms of Reynolds number (Re) sensitivity for such probes. In order to close this gap, detailed investigations of the effect of Re on a five-hole probe have been performed using both PIV techniques and oil flow visualizations. Wind- and water-tunnels were used to cover a wide range of Re. The open-access Oxford Probe was used for these studies because of the readily available data-sets and processing routines, and to allow future comparisons by other authors. Complex flow dynamics including flow separation and re-attachment were identified, which cause Re-sensitivity of the calibration map at low Re even for low yaw or pitch angles. By comparing calibration maps across a wide range of Re, we demonstrate that the Oxford Probe can be employed without much loss of accuracy at lower Re levels than initially (conservatively) suggested, and quantify the errors in the extreme low-Re regime. Overall we demonstrate the robustness of the Oxford Probe concept across a wide range of Re conditions, we more clearly defined the low-Re limit for the probe design and quantify errors below this limit, and we illustrate the fundamental mechanisms for Re-sensitivity of multi-hole probes.

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Study of Flow Through a Stationary Ribbed Channel for Blade Cooling

Volume 4: Heat Transfer, Parts A and B ◽

10.1115/gt2010-23031 ◽

2010 ◽

Cited By ~ 4

Author(s):

R. S. Amano ◽

Krishna Guntur ◽

Jose Martinez Lucci ◽

Yu Ashitaka

Keyword(s):

Heat Transfer ◽

Reynolds Number ◽

Firing Temperature ◽

Turbulence Models ◽

Flow Patterns ◽

Higher Order ◽

Secondary Flows ◽

Complex Flow ◽

Cooling Channels ◽

Blade Cooling

The firing temperature in gas turbine relates itself directly to the power output and the efficiency of the turbine. The higher the firing (operating) temperatures, higher the wall temperature of blades. However, an increase in the firing temperature is limited by the first stage blade material properties. This is because the higher firing temperature may cause a creep rupture, oxidizing, melting and ultimately failing of blades. Prior to blade cooling, the firing temperature was the same as the blade material temperature. Advancements in cooling technology have resulted in high firing temperatures with acceptable material temperatures. To better design the cooling channels and to improve heat transfer, many researchers are studying the flow patterns inside the cooling channels both experimentally and computationally. In this paper, the authors present the performance of three turbulence models using a Computational Fluid Dynamics code in comparison with the experimental values. To test the performance, a square duct was used with rectangular ribs oriented at 90° and 45° degree and placed at regular intervals. The channel also has bleed holes. The wall Nusselt numbers are compared in both the experimental and the computational results after suitable normalization. The Reynolds number is set to 10,000. The interactions between secondary flows and separation lead to very complex flow patterns. To accurately simulate these flows and heat transfer, both refined turbulence models and higher-order numerical schemes are indispensable for turbine designers to improve the cooling performance. The three-dimensional turbulent flows and heat transfer are numerically studied by using several different turbulence models, such as a non-linear low-Reynolds number k-ω and Reynolds Stress (RSM) models. In the k-ω model the cubic terms are included to represent the effects of extra strain-rates such as streamline curvature and three-dimensionality on both normal and shear turbulence stresses. The finite volume difference method incorporated with the higher-order bounded interpolation scheme has been employed in the present study. The outcome of this study helps to determine the best suitable turbulence model for future studies.

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Flow dynamics and wall-pressure signatures in a high-Reynolds-number overexpanded nozzle with free shock separation

Journal of Fluid Mechanics ◽

10.1017/jfm.2020.280 ◽

2020 ◽

Vol 895 ◽

Cited By ~ 1

Author(s):

E. Martelli ◽

L. Saccoccio ◽

P. P. Ciottoli ◽

C. E. Tinney ◽

W. J. Baars ◽

...

Keyword(s):

Reynolds Number ◽

High Reynolds Number ◽

Wall Pressure ◽

Flow Dynamics ◽

Free Shock Separation ◽

High Reynolds ◽

Image Position ◽

Free Shock

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Stability Analysis of Hydropower Stations With Complex Flow Patterns in the Tailrace Tunnel

Volume 2, Fora: Cavitation and Multiphase Flow; Fluid Measurements and Instrumentation; Microfluidics; Multiphase Flows: Work in Progress ◽

10.1115/fedsm2013-16617 ◽

2013 ◽

Cited By ~ 1

Author(s):

Jianxu Zhou ◽

Fulin Cai ◽

Ming Hu

Keyword(s):

Free Surface ◽

Stability Analysis ◽

Flow Patterns ◽

Normal Operation ◽

Complex Flow ◽

Diversion Tunnel ◽

Implicit Model ◽

Special Cases ◽

Tailrace Tunnel ◽

Hydropower Stations

For some special tailrace tunnels in the hydropower stations, including the changing top-altitude tailrace tunnel and the tailrace tunnel with downstream reused flat-ceiling diversion tunnel, during normal operation and hydraulic transients, the flow patterns inside are relatively complex mainly including the free-surface pressurized flow and partial free flow if the tail water level is lower than the top elevation of tunnel’s outlet. These complex flow patterns have obvious effect on system’s stability, and can not be simulated accurately by the traditional models. Therefore, a characteristic implicit model is introduced to simulate these complex flow patterns for further stability analysis. In some special cases, the characteristic implicit model also fails to completely simulate the mixed free-surface pressurized flow in the flat-ceiling tailrace tunnel. A new method is presented based on both experimental research and numerical simulation, and then, system’s stability is analyzed by compared with traditional ordinary boundary condition. The results indicate that, with different simulation models for the complex water flow in the tailrace tunnel, system’s dynamic characteristic can be actually revealed with the consideration of the effect of complex flow patterns in the tailrace tunnel on system’s stability and regulation performance.

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