An Experimental Study of Natural Convection in a Toroidal Loop

1988 ◽  
Vol 110 (4a) ◽  
pp. 877-884 ◽  
Author(s):  
C. H. Stern ◽  
R. Greif ◽  
J. A. C. Humphrey
Keyword(s):  
Experimental Study ◽  
Three Dimensional ◽  
Secondary Flows ◽  
Laser Doppler Velocimeter ◽  
Temperature Profiles ◽  
Flow Conditions ◽  
Velocity Measurements ◽  
Heating Section ◽  
Thermocouple Probe ◽  
Flow Reversals

Velocity and temperature profiles were measured at the entrance and exit to the heating section of a toroidal thermosyphon loop operating under steady flow conditions for a range of heat inputs. Velocity measurements were made with a laser-Doppler velocimeter and temperature measurements with a small thermocouple probe. Detailed results are presented for the longitudinal and circumferential components of the velocity for four heat inputs. The data for cross-stream secondary flows and streamwise flow reversals emphasize the importance of including three-dimensional effects in analyses of these systems.

The Effect of Stator-Rotor Hub Sealing Flow on the Mainstream Aerodynamics of a Turbine

2006 ◽  
Author(s):  
Kevin Reid ◽  
John Denton ◽  
Graham Pullan ◽  
Eric Curtis ◽  
John Longley
Keyword(s):  
Steady State ◽  
Entropy Generation ◽  
Flow Rate ◽  
Three Dimensional ◽  
Secondary Flows ◽  
Flow Conditions ◽  
Turbine Efficiency ◽  
Turbine Performance ◽  
Mainstream Flow ◽  
Flow Interactions

An investigation into the effect of stator-rotor hub gap sealing flow on turbine performance is presented. Efficiency measurements and rotor exit area traverse data from a low speed research turbine are reported. Tests carried out over a range of sealing flow conditions show that the turbine efficiency decreases with increasing sealant flow rate but that this penalty is reduced by swirling the sealant flow. Results from time-accurate and steady-state simulations using a three-dimensional multi-block RANS solver are presented with particular emphasis paid to the mechanisms of loss production. The contributions toward entropy generation of the mixing of the sealant fluid with the mainstream flow and of the perturbed rotor secondary flows are assessed. The importance of unsteady stator wake/sealant flow interactions is also highlighted.

Numerical Simulation of the Flow in a Toroidal Thermosiphon

2011 ◽  
Author(s):  
Elia Merzari ◽  
Paul Fischer ◽  
Hisashi Ninokata
Keyword(s):  
Three Dimensional ◽  
Heat Removal ◽  
Spectral Element ◽  
Velocity Measurements ◽  
Dimensional Effects ◽  
Buoyancy Driven Flows ◽  
Rans Modeling ◽  
The Stability ◽  
Flow Reversals ◽  
Residual Heat

Buoyancy-driven flows are widespread in diverse engineering applications. Such flows have been studied in great detail theoretically, experimentally, and numerically. The prototype of passive, residual heat removal systems is the toroidal thermosiphon. The stability properties of such systems were first examined in detail by Creveling et al. in the mid-1970s, who reported flow reversals and instability in this geometry. Traditionally, however, the stability analysis of natural convection loops has been confined to one-dimensional calculations, on the argument that the flow would be monodimensional when the ratio between the radius of the loop and the radius of the pipe is much larger than 1. Nevertheless, accurate velocity measurements of the flow in toroidal loops have shown that the flow presents three-dimensional effects. In the present work we analyze the stability problem in a toroidal loop and then use computational fluid dynamics to evaluate the relative importance of these three-dimensional effects with regard to stability. We performed a series of high-fidelity numerical simulations using the spectral element code Nek5000. We compared the results to the available data and calculations performed with the code STAR-CCM+ 5.06. The results show a much richer dynamics than expected from either previous calculations or stability theory. The results also point to some outstanding issues in the RANS modeling of such flows.

Determination of the Pressure Field Using Three-Dimensional, Volumetric Velocity Measurements

2016 ◽  
Vol 138 (8) ◽  
Author(s):  
Hansheng Pan ◽  
Sheila H. Williams ◽  
Paul S. Krueger
Keyword(s):  
Poisson Equation ◽  
Temporal Resolution ◽  
Pressure Field ◽  
Three Dimensional ◽  
Vortical Flow ◽  
Flow Conditions ◽  
Velocity Measurements ◽  
Pressure Poisson Equation ◽  
Computational Fluid Dynamics Cfd

Methods to determine the pressure field of vortical flow from three-dimensional (3D) volumetric velocity measurements (e.g., from a TSI V3VTM system) are discussed. The boundary pressure was determined where necessary using the unsteady Bernoulli equation for both line integration and pressure Poisson equation methods. Error analysis using computational fluid dynamics (CFD) data was conducted to investigate the effects of spatial resolution, temporal resolution, and velocity error levels. The line integration method was more sensitive to temporal resolution, while the pressure Poisson equation method was more sensitive to boundary flow conditions. The latter was generally more suitable for V3VTM velocity measurements.

Pressure and Three-Component Velocity Measurements on a Diffuser That Generates Longitudinal Vortices

1990 ◽  
Vol 112 (3) ◽  
pp. 281-288
Author(s):  
L. N. Goenka ◽  
R. L. Panton ◽  
D. G. Bogard
Keyword(s):  
Static Pressure ◽  
Three Dimensional ◽  
Quantitative Information ◽  
Pressure Recovery ◽  
Laser Doppler Velocimeter ◽  
Velocity Measurements ◽  
Longitudinal Vortices ◽  
Transverse Pressure ◽  
Component Velocity ◽  
Flow Oscillations

This paper presents flowfield measurements on a wide-angle, three-dimensional diffuser that has a vastly improved static-pressure recovery over the corresponding plane-wall diffuser when discharging into a plenum. The diffuser geometry consists of a pyramid-shaped insert attached to the diffuser expansion wall. The upsweep on the upper surface of the pyramid generates a transverse pressure gradient that causes the incoming flow to roll up into two symmetric, longitudinal vortices. Earlier flow-visualization studies have shown that these vortices replace the closed separated regions along the diffuser expansion wall, eliminating flow oscillations and hysteresis. This paper presents quantitative information, in the form of static pressure, total pressure, and three-component Laser Doppler Velocimeter (LDV) measurements, on the diffuser flowfield for two variations in the pyramid geometry. Information from these studies is useful in developing configurations with enhanced pressure recoveries. The greatly improved static-pressure recovery of this diffuser, combined with its superior flowfield features, make it particularly suitable for exhaust diffuser applications.

Computational Fluid Dynamics Simulation of a Single-Phase Rectangular Thermosiphon

2020 ◽  
Author(s):  
Tri Nguyen ◽  
Elia Merzari
Keyword(s):  
Single Phase ◽  
Fluid Dynamic ◽  
Three Dimensional ◽  
Heat Removal ◽  
Spectral Element ◽  
Dynamics Simulation ◽  
Velocity Measurements ◽  
Buoyancy Driven Flows ◽  
The Stability ◽  
Flow Reversals

Abstract Buoyancy-driven flows are widespread in diverse engineering applications. Such flows have been studied in great detail theoretically, experimentally, and numerically. However, the fluid-dynamic instabilities and flow reversals of thermosiphon are still actively investigated. The presence of such instabilities limits the effectiveness of such devices for decay heat removal. Traditionally the stability analysis of natural convection loops has been confined to one-dimensional calculations, on the argument that the flow would be mono-dimensional when the ratio between the radius of the loop and the radius of the pipe is much larger than 1. Nevertheless, accurate velocity measurements of the flow in toroidal loops have shown that the flow presents three-dimensional effects. Previous works of the authors have shown that these structures can be seen in thermosiphons. In this paper, we aim to use modern CFD methods to investigate the three-dimensional flow in thermosiphons. This paper focuses on rectangular thermosiphons. In particular, we perform a series of high-fidelity simulations using the spectral element code Nek5000 to investigate the stability behavior of the flow in a rectangular thermosiphon. We compare the results with available existing experimental data from the L2 facility in Genoa. We examine in detail the flow structures generated. Moreover, in the past various authors have demonstrated that the overall behavior of the thermosiphon depends strongly on the boundary conditions (BCs). The simulation campaign was carried out with different BCs to investigate and confirm this effect. In particular, simulations with Dirichlet, Neumann and Robin BCs for heater and sink were performed.

Operational Model and its Validation with Drift Tests in Water Areas Around the Baltic Sea

1994 ◽  
Vol 29 (2-3) ◽  
pp. 293-308
Author(s):  
J. Koponen ◽  
M. Virtanen ◽  
H. Vepsä ◽  
E. Alasaarela
Keyword(s):  
Three Dimensional ◽  
Fast Response ◽  
Velocity Measurements ◽  
Short Term ◽  
Large Lakes ◽  
Operational Model ◽  
Water Currents ◽  
Emergency Situations ◽  
Sensitivity Tests ◽  
The Baltic

Abstract Three-dimensional (3-D) mathematical models of water currents, transport, mixing, reaction kinetic, and interactions with bottom and air have been used in Finland regularly since 1982 and applied to about 40 cases in large lakes, inland seas and their coastal waters. In each case, model validity has been carefully tested with available flow velocity measurements, tracer studies and water quality observations. For operational use, i.e., for spill combatting and sea rescue, the models need fast response, proven validity and illustrative visualization. In 1987-90, validated models were implemented for operational use at five sea areas along the Finnish coast. Further validation was obtained in model applications from nine documented or arranged cases and from seven emergency situations. Sensitivity tests supplement short-term validation. In the Bothnian Sea, it was nescessary to start the calculation of water currents three days prior to the start of the experiment to reduce initial inaccuracies and to make the coastal transport estimates meaningful.

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