Modeling of Turbulent Flows Through the Annular Channel with Eccentricity and Rotating Inner Cilinder

2012 ◽  
Vol 7 (4) ◽  
pp. 79-86
Author(s):  
Evgeny Podryabinkin ◽  
Valeriy Rudyak
Keyword(s):  
Pressure Drop ◽  
Turbulent Flows ◽  
Transport Model ◽  
Reverse Flow ◽  
Axial Flow ◽  
Annular Channel ◽  
Rotational Flow ◽  
Concentric Annulus ◽  
Cylindrical Annulus ◽  
Wide Range

In this paper fully developed turbulent flows of Newtonian fluid in cylindrical annulus with eccentricity and rotating inner cylinder has been systematically studied. Modeling has been performed on the base of Menter Shear Transport model of turbulence in a wide range of Reynolds numbers, eccentricity, and radii ratio. As the result dependencies of flow field and pressure drop along the channel on geometrical and flow parameters have been found. It was shown that flow characteristics and dependence of the pressure drop are determined by which flow axial or rotational dominates and caused generation of turbulence. When rotational flow dominates the dependence of the pressure drop is almost linear. When axial flow dominates rotation practically has no impact on the pressure drop in concentric annulus. Appearance of the reverse flow in eccentric channel has a major impact on the pressure drop. In case when rotational flow dominates, appearance of the reverse flow is accompanied by threshold flow restructuring at some critical value of eccentricity. A correlation for determination of the pressure drop in various regimes has been developed for the case of concentric annulus

Modeling of Turbulent Flows Through the Annular Channel with Eccentricity and Rotating Inner Cilinder

2012 ◽  
Vol 7 (4) ◽  
pp. 79-86
Author(s):  
Evgeny Podryabinkin ◽  
Valeriy Rudyak
Keyword(s):  
Pressure Drop ◽  
Turbulent Flows ◽  
Transport Model ◽  
Reverse Flow ◽  
Axial Flow ◽  
Annular Channel ◽  
Rotational Flow ◽  
Concentric Annulus ◽  
Cylindrical Annulus ◽  
Wide Range

In this paper fully developed turbulent flows of Newtonian fluid in cylindrical annulus with eccentricity and rotating inner cylinder has been systematically studied. Modeling has been performed on the base of Menter Shear Transport model of turbulence in a wide range of Reynolds numbers, eccentricity, and radii ratio. As the result dependencies of flow field and pressure drop along the channel on geometrical and flow parameters have been found. It was shown that flow characteristics and dependence of the pressure drop are determined by which flow axial or rotational dominates and caused generation of turbulence. When rotational flow dominates the dependence of the pressure drop is almost linear. When axial flow dominates rotation practically has no impact on the pressure drop in concentric annulus. Appearance of the reverse flow in eccentric channel has a major impact on the pressure drop. In case when rotational flow dominates, appearance of the reverse flow is accompanied by threshold flow restructuring at some critical value of eccentricity. A correlation for determination of the pressure drop in various regimes has been developed for the case of concentric annulus

Sensitization of the SST Turbulence Model to Rotation and Curvature by Applying the Spalart–Shur Correction Term

2009 ◽  
Vol 131 (4) ◽  
Author(s):  
Pavel E. Smirnov ◽  
Florian R. Menter
Keyword(s):  
Turbulent Flows ◽  
Turbulence Model ◽  
Transport Model ◽  
Correction Term ◽  
Computational Cost ◽  
Turbulence Models ◽  
Reynolds Stress Transport Model ◽  
Wide Range ◽  
Sst Model ◽  
The One

A rotation-curvature correction suggested earlier by Spalart and Shur (1997, “On the Sensitization of Turbulence Models to Rotation and Curvature,” Aerosp. Sci. Technol., 1(5), pp. 297–302) for the one-equation Spalart–Allmaras turbulence model is adapted to the shear stress transport model. This new version of the model (SST-CC) has been extensively tested on a wide range of both wall-bounded and free shear turbulent flows with system rotation and/or streamline curvature. Predictions of the SST-CC model are compared with available experimental and direct numerical simulations (DNS) data, on the one hand, and with the corresponding results of the original SST model and advanced Reynolds stress transport model (RSM), on the other hand. It is found that in terms of accuracy the proposed model significantly improves the original SST model and is quite competitive with the RSM, whereas its computational cost is significantly less than that of the RSM.

Heat Transfer and Pressure Drop Correlations for Twisted-Tape Inserts in Isothermal Tubes: Part II—Transition and Turbulent Flows

1993 ◽  
Vol 115 (4) ◽  
pp. 890-896 ◽  
Author(s):  
R. M. Manglik ◽  
A. E. Bergles
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Turbulent Flows ◽  
Published Data ◽  
Twisted Tape ◽  
Heating And Cooling ◽  
Twisted Tapes ◽  
Family Of Curves ◽  
Wide Range ◽  
Limiting Case

Thermal-hydraulic design correlations are developed to predict isothermal f and Nu for in-tube, turbulent flows with twisted-tape inserts. Experimental data taken for water and ethylene glycol, with y = 3.0, 4.5, and 6.0, are analyzed, and various mechanisms attributed to twisted tapes are identified. Tube blockage and tape-induced vortex mixing are the dominant phenomena that result in increased heat transfer and pressure drop; for loose- to snug-fitting tapes, the fin effects are insignificant. The limiting case of a straight tape insert correlates with the hydraulic-diameter-based smooth tube equation. Tape twist effects are thus isolated by normalizing the data with the asymptotic predictions for y = ∞, and the swirl effects are found to correlate with Re and l/y. The validity of the final correlations is verified by comparing the predictions with previously published data, which include both gases and liquids, under heating and cooling conditions and a wide range of tape geometries, thereby establishing a very generalized applicability. Finally, correlations for laminar (presented in the companion Part I paper) and turbulent flows are combined into single, continuous equations. For isothermal f, the correlation describes most of the available data for laminar-transition-turbulent flows within ±10 percent. For Nu, however, a family of curves is needed due to the nonunique nature of laminar-turbulent transition.

Sensitization of the SST Turbulence Model to Rotation and Curvature by Applying the Spalart-Shur Correction Term

2008 ◽  
Author(s):  
Pavel E. Smirnov ◽  
Florian R. Menter
Keyword(s):  
Turbulent Flows ◽  
Turbulence Model ◽  
Transport Model ◽  
Correction Term ◽  
Computational Cost ◽  
Reynolds Stresses ◽  
Wide Range ◽  
Sst Model ◽  
Shear Stress Transport Model ◽  
Sst Turbulence Model

A rotation-curvature correction suggested earlier by Spalart and Shur for the one-equation Spalart-Allmaras turbulence model is adapted to the Shear Stress Transport model. This new version of the model (SST-CC) has been extensively tested on a wide range of both wall-bounded and free shear turbulent flows with system rotation and/or streamline curvature. Predictions of the SST-CC model are compared with available experimental and DNS data, on one hand, and with the corresponding results of the original SST model and advanced Reynolds stresses transport model (RSM), on the other hand. It is found, that in terms of accuracy the proposed model significantly improves the original SST model and is quite competitive with the RSM, whereas its computational cost is significantly less than that of the RSM.

Numerical Characterization of Hot Gas Ingestion Through Turbine Rim Seals

2016 ◽  
Author(s):  
Riccardo Da Soghe ◽  
Cosimo Bianchini ◽  
Carl M. Sangan ◽  
James A. Scobie ◽  
Gary D. Lock
Keyword(s):  
Flow Rate ◽  
Numerical Study ◽  
Axial Flow ◽  
Radial Clearance ◽  
Buffering Effect ◽  
Hot Gas ◽  
Numerical Predictions ◽  
Wide Range ◽  
Thermal Buffering

This paper deals with a numerical study aimed at the characterization of hot gas ingestion through turbine rim seals. The numerical campaign focused on an experimental facility which models ingress through the rim seal into the upstream wheel-space of an axial-turbine stage. Single-clearance arrangements were considered in the form of axial- and radial-seal gap configurations. With the radial-seal clearance configuration, CFD steady-state solutions were able to predict the system sealing effectiveness over a wide range of coolant mass flow rates reasonably well. The greater insight of flow field provided by the computations illustrates the thermal buffering effect when ingress occurs: for a given sealing flow rate, the effectiveness on the rotor was significantly higher than that on the stator due to the axial flow of hot gases from stator to rotor caused by pumping effects. The predicted effectiveness on the rotor was compared with a theoretical model for the thermal buffering effect showing good agreement. When the axial-seal clearance arrangement is considered, the agreement between CFD and experiments worsens; the variation of sealing effectiveness with coolant flow rate calculated by means of the simulations display a distinct kink. It was found that the “kink phenomenon” can be ascribed to an over-estimation of the egress spoiling effects due to turbulence modelling limitations. Despite some weaknesses in the numerical predictions, the paper shows that CFD can be used to characterize the sealing performance of axial- and radial-clearance turbine rim seals.

Compact Modeling of Forced Flow in Longitudinal Fin Heat Sinks With Tip Bypass

2003 ◽  
Vol 125 (3) ◽  
pp. 319-324 ◽  
Author(s):  
C. B. Coetzer ◽  
J. A. Visser
Keyword(s):  
Pressure Drop ◽  
Heat Sink ◽  
Heat Sinks ◽  
Compact Model ◽  
Forced Flow ◽  
Compact Modeling ◽  
Transfer Coefficients ◽  
Wide Range ◽  
Laminar And Turbulent Flow ◽  
Improved Accuracy

This paper introduces a compact model to predict the interfin velocity and the resulting pressure drop across a longitudinal fin heat sink with tip bypass. The compact model is based on results obtained from a comprehensive study into the behavior of both laminar and turbulent flow in longitudinal fin heat sinks with tip bypass using CFD analysis. The new compact flow prediction model is critically compared to existing compact models as well as to the results obtained from the CFD simulations. The results indicate that the new compact model shows at least a 4.5% improvement in accuracy predicting the pressure drop over a wide range of heat sink geometries and Reynolds numbers simulated. The improved accuracy in velocity distribution between the fins also increases the accuracy of the calculated heat transfer coefficients applied to the heat sinks.

Influence of Turbulent Flow Characteristics and Coherent Vortices on the Pressure Recovery of Annular Diffusers: Part A — Experimental Results

2015 ◽  
Author(s):  
Marcus Kuschel ◽  
Bastian Drechsel ◽  
David Kluß ◽  
Joerg R. Seume
Keyword(s):  
Boundary Layer ◽  
High Pressure ◽  
Static Pressure ◽  
Turbulent Transport ◽  
Axial Flow ◽  
Pressure Recovery ◽  
Turbulence Structure ◽  
Reynolds Stresses ◽  
Wide Range ◽  
Operating Points

Exhaust diffusers downstream of turbines are used to transform the kinetic energy of the flow into static pressure. The static pressure at the turbine outlet is thus decreased by the diffuser, which in turn increases the technical work as well as the efficiency of the turbine significantly. Consequently, diffuser designs aim to achieve high pressure recovery at a wide range of operating points. Current diffuser design is based on conservative design charts, developed for laminar, uniform, axial flow. However, several previous investigations have shown that the aerodynamic loading and the pressure recovery of diffusers can be increased significantly if the turbine outflow is taken into consideration. Although it is known that the turbine outflow can reduce boundary layer separations in the diffuser, less information is available regarding the physical mechanisms that are responsible for the stabilization of the diffuser flow. An analysis using the Lumley invariance charts shows that high pressure recovery is only achieved for those operating points in which the near-shroud turbulence structure is axi-symmetric with a major radial turbulent transport component. This turbulent transport originates mainly from the wake and the tip vortices of the upstream rotor. These structures energize the boundary layer and thus suppress separation. A logarithmic function is shown that correlates empirically the pressure recovery vs. the relevant Reynolds stresses. The present results suggest that an improved prediction of diffuser performance requires modeling approaches that account for the anisotropy of turbulence.

Sulfuric acid vapor and sulfur dioxide in the atmosphere of Venus as observed by the Venus Express Radio Science Experiment VeRa

2021 ◽  
Author(s):  
Janusz Oschlisniok ◽  
Bernd Häusler ◽  
Martin Pätzold ◽  
Silvia Tellmann ◽  
Michael Bird
Keyword(s):  
Sulfuric Acid ◽  
Transport Model ◽  
Lower Atmosphere ◽  
Local Times ◽  
Acid Vapor ◽  
Radio Science ◽  
X Band ◽  
Wide Range ◽  
Venus Express ◽  
Atmosphere Of Venus

<p>The main cloud deck within Venus' atmosphere, which covers the entire planet between approx. 50 and 70 km altitude, is believed to consist mostly of liquid sulfuric acid. The temperature below the main clouds is high enough to evaporate the H2SO4 droplets into gaseous sulfuric acid forming a haze layer which extends to altitudes as deep as 35 km. Gaseous sulfuric acid in Venus’ lower atmosphere is responsible for a strong absorption of radio waves as seen in Mariner, Pioneer Venus, Magellan and Venera radio science observations. Radio wave absorption measurements can be used to derive the amount of H2SO4 in Venus’ atmosphere. The radio science experiment VeRa onboard Venus Express probed the atmosphere of Venus between 2006 and 2014 with radio signals at 13 cm (S-band) and 3.6 cm (X-band) wavelengths. The orbit of the Venus Express spacecraft allowed to sound the atmosphere over a wide range of latitudes and local times providing a global picture of the sulfuric acid vapor distribution. We present the global H2SO4(g) distribution derived from the X-band radio signal attenuation for the time of the entire Venus Express mission. The observation is compared with results obtained from a 2-D transport model. The VeRa observations were additionally used to estimate the abundance of SO2 near the cloud bottom. The global distribution of SO2 at these altitudes is presented and compared with results obtained from other experiments. Eight years of VEX observation allow to study the long-term evolution of H2SO4 and SO2. The latter is presented for the northern polar region.</p>

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