Predicted Secondary Flows in Triangular Array Rod Bundles

1979 ◽  
Vol 101 (3) ◽  
pp. 354-362 ◽  
Author(s):  
A. C. Trupp ◽  
A. M. M. Aly
Keyword(s):  
Secondary Flow ◽  
Reynolds Numbers ◽  
Flow Cell ◽  
Secondary Flows ◽  
Rod Bundles ◽  
Primary Flow ◽  
Friction Factors ◽  
Fully Developed Turbulent Flow ◽  
Flow Through ◽  
Stress Variations

A one-equation turbulence model was applied to forecast the main features of fully-developed turbulent flow through infinite equilateral triangular arrays of parallel rods having pitch-to-diameter ratios of 1.12 – 1.35 and Reynolds numbers of (2.7 – 25) × 104. For all cases, the secondary flow was found to be a single cell of circulation for each primary flow cell of a subchannel. The strength of the secondary flow increased with Reynolds number but decreased with rod spacing. The numerical results (which included friction factors, wall shear stress variations and axial velocity distributions) are shown to be in reasonable agreement with published experimental data.

Effects of Dimple Depth on Nusselt Numbers and Friction Factors for Internal Cooling in a Channel

2004 ◽  
Author(s):  
N. K. Burgess ◽  
P. M. Ligrani
Keyword(s):  
Reynolds Number ◽  
Nusselt Number ◽  
Local Nusselt Number ◽  
Reynolds Numbers ◽  
Secondary Flows ◽  
Channel Height ◽  
Stagnation Temperature ◽  
Nusselt Numbers ◽  
Number Ratio ◽  
Friction Factors

Experimental results, measured on dimpled test surfaces placed on one wall of different channels, are given for a ratio of air inlet stagnation temperature to surface temperature of approximately 0.94, and Reynolds numbers based on channel height from 9,940 to 74,800. The data presented include friction factors, local Nusselt numbers, spatially-averaged Nusselt numbers, and globally-averaged Nusselt numbers. The ratios of dimple depth to dimple print diameter δ/D are 0.1, 0.2, and 0.3 to provide information on the influences of dimple depth. The ratio of channel height to dimple print diameter is 1.00. At all Reynolds numbers considered, local and spatially-resolved Nusselt number augmentations increase as dimple depth increases (and all other experimental and geometric parameters are held approximately constant). These are attributed to: (i) increases in the strengths and intensity of vortices and associated secondary flows ejected from the dimples, as well as (ii) increases in the magnitudes of three-dimensional turbulence production and turbulence transport. The effects of these phenomena are especially apparent in local Nusselt number ratio distributions measured just inside of the dimples, and just downstream of the downstream edges of the dimples. Data are also presented to illustrate the effects of Reynolds number, and streamwise development for δ/D = 0.1 dimples. Significant local Nusselt number ratio variations are observed at different streamwise locations, whereas variations with Reynolds number are mostly apparent on flat surfaces just downstream of individual dimples.

Visualization Study of Flow in Axial Flow Inducer

1972 ◽  
Vol 94 (4) ◽  
pp. 777-787 ◽  
Author(s):  
B. Lakshminarayana
Keyword(s):  
Radial Velocity ◽  
Secondary Flow ◽  
Three Dimensional ◽  
Axial Flow ◽  
Flow Theory ◽  
Secondary Flows ◽  
Flow Coefficient ◽  
Flow Through

A visualization study of the flow through a three ft dia model of a four bladed inducer, which is operated in air at a flow coefficient of 0.065, is reported in this paper. The flow near the blade surfaces, inside the rotating passages, downstream and upstream of the inducer is visualized by means of smoke, tufts, ammonia filament, and lampblack techniques. Flow is found to be highly three dimensional, with appreciable radial velocity throughout the entire passage. The secondary flows observed near the hub and annulus walls agree with qualitative predictions obtained from the inviscid secondary flow theory. Based on these investigations, methods of modeling the flow are discussed.

Vane Suction Surface Heat Transfer in Regions of Secondary Flows: The Influence of Turbulence Level, Reynolds Number and the Endwall Boundary Condition

2017 ◽  
Author(s):  
J. Varty ◽  
L. W. Soma ◽  
F. E. Ames ◽  
S. Acharya
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Boundary Condition ◽  
Secondary Flow ◽  
Reynolds Numbers ◽  
High Heat ◽  
Surface Heat ◽  
Secondary Flows ◽  
Suction Surface ◽  
High Heat Transfer

Secondary flows in vane passages sweep off the endwall and onto the suction surface at a location typically close to the throat. These endwall/vane junction flows often have an immediate impact on heat transfer in this region and also move any film cooling off the affected region of the vane. The present paper documents the impact of secondary flows on suction surface heat transfer acquired over a range of turbulence levels (0.7% through 17.4%) and a range of exit chord Reynolds numbers (500,000 through 2,000,000). Heat transfer data are acquired with both an unheated endwall boundary condition and a heated endwall boundary condition. The vane design includes an aft loaded suction surface and a large leading edge diameter. The unheated endwall boundary condition produces initially very high heat transfer levels due to the thin thermal boundary layer starting at the edge of heating. This unheated starting length effect quickly falls off with the thermal boundary layer growth as the secondary flow sweeps up onto the vane suction surface. The heat transfer visualization for the heated endwall condition shows no initial high heat transfer level near the edge of heating on the vane. The heat transfer level in the region affected by the secondary flows is largely uniform, except for a notable depression in the affected region. This heat transfer depression is believed due to an upwash region generated above the separation line of the passage vortex, likely in conjunction with the counter rotating suction leg of the horseshoe vortex. The extent and definition of the secondary flow affected region on the suction surface is clearly evident at lower Reynolds numbers and lower turbulence levels when the suction surface flow is largely laminar. The heat transfer in the plateau region has a magnitude similar to a turbulent boundary layer. However, the location and extent of this secondary flow affected region is less perceptible at higher turbulence levels where transitional or turbulent flow is present. Also, aggressive mixing at higher turbulence levels serves to smooth out discernable differences in the heat transfer due to the secondary flows.

scholarly journals Numerical Study of Turbulent Secondary Flows in Curved Ducts

1990 ◽  
Vol 112 (2) ◽  
pp. 205-211 ◽  
Author(s):  
N. Hur ◽  
S. Thangam ◽  
C. G. Speziale
Keyword(s):  
Experimental Data ◽  
Turbulent Flow ◽  
Secondary Flow ◽  
Cross Section ◽  
Numerical Study ◽  
Secondary Flows ◽  
Fully Developed Turbulent Flow ◽  
Volume Method ◽  
Curved Ducts ◽  
Good Agreement

The pressure driven, fully developed turbulent flow of an incompressible viscous fluid in curved ducts of square cross-section is studied numerically by making use of a finite volume method. A nonlinear K -1 model is used to represent the turbulence. The results for both straight and curved ducts are presented. For the case of fully developed turbulent flow in straight ducts, the secondary flow is characterized by an eight-vortex structure for which the computed flowfield is shown to be in good agreement with available experimental data. The introduction of moderate curvature is shown to cause a substantial increase in the strength of the secondary flow and to change the secondary flow pattern to either a double-vortex or a four-vortex configuration.

Module Friction Factors and Intramodular Pressure Distributions for Periodic Fully Developed Turbulent Flow in Rectangular Interrupted-Plate Ducts

1988 ◽  
Vol 110 (2) ◽  
pp. 147-154 ◽  
Author(s):  
R. K. McBrien ◽  
B. R. Baliga
Keyword(s):  
Turbulent Flows ◽  
Static Pressure ◽  
Rectangular Cross Section ◽  
Reynolds Numbers ◽  
Plate Spacing ◽  
Pressure Distributions ◽  
Geometric Configurations ◽  
Friction Factors ◽  
Mean Pressure ◽  
Fully Developed Turbulent Flow

This paper presents detailed time-mean pressure measurements for periodic fully developed turbulent flows in straight interrupted-plate ducts of rectangular cross section. Several combinations of plate spacing and duct aspect ratio are investigated for Reynolds numbers, based on a module hydraulic diameter, in the range 5000 to 45000. The experiments undertaken in this work establish the existence of steady, time-mean, periodic fully developed flows for all flow rates and geometric configurations investigated. The results include graphical and tabular presentations of module friction factor versus Reynolds number data, and intramodular time-mean wall static pressure distributions. The physical implications of these results are also discussed.

Influence of Crossflow-Induced Swirl and Impingement on Heat Transfer in an Internal Coolant Passage of a Turbine Airfoil

2000 ◽  
Vol 122 (3) ◽  
pp. 587-597 ◽  
Author(s):  
S. V. Ekkad ◽  
G. Pamula ◽  
S. Acharya
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Reynolds Numbers ◽  
Secondary Flows ◽  
Transfer Enhancement ◽  
Feed System ◽  
Nusselt Numbers ◽  
Flow Through ◽  
Transient Liquid Crystal Technique ◽  
Measured Pressure

Detailed heat transfer distributions are presented inside a two-pass coolant channel with crossflow-induced swirl and impingement. The impingement and passage crossflow are generated from one coolant passage to the adjoining coolant passage through a series of straight or angled holes along the dividing wall. The holes provide for the flow turning from one passage to another typically achieved in a conventional design by a 180-deg U-bend. The holes direct the flow laterally from one passage to another and generate different secondary flow patterns in the second pass. These secondary flows produce impingement and swirl and lead to higher heat transfer enhancement. Three different lateral hole configurations are tested for three Reynolds numbers (Re=10,000, 25,000, 50,000). The configurations were varied by angle of delivery and location on the divider wall. A transient liquid crystal technique is used to measure the detailed heat transfer coefficient distributions inside the passages. Results with the new crossflow feed system are compared with the results from the traditional 180-deg turn passage. Results show that the crossflow feed configurations produce significantly higher Nusselt numbers on the second pass walls without affecting the first pass heat transfer levels. The heat transfer enhancement is as high as seven to eight times greater than obtained in the second pass for a channel with a 180-deg turn. The increased measured pressure drop (rise in friction factor) caused by flow through the crossflow holes are compensated by the significant heat transfer enhancement obtained by the new configuration. [S0022-1481(00)03103-0]

Development of Cavity Shapes of Labyrinth Seals Through CFD Analysis

2013 ◽  
Author(s):  
Mohana Rao Ramanadham ◽  
Balakrishna Gaja ◽  
Sravan Kumar Kanchanapally
Keyword(s):  
Secondary Flow ◽  
Gas Turbines ◽  
Axial Flow ◽  
Labyrinth Seal ◽  
Geometric Shape ◽  
Working Fluid ◽  
Leakage Flow ◽  
Labyrinth Seals ◽  
Primary Flow ◽  
Flow Through

Axial flow compressors of Gas turbines use labyrinth seals to prevent the backflow of the working fluid. However some fluid will leak through the seals due to the clearance provided between the stationery and rotating components and due to the pressure difference across the seals, which affects the efficiency. The geometric shape of the seal plays an important role in influencing the fluid flow through the seals and the leakage rate. The flow through the seals consists of the primary flow and the secondary flow. The secondary flow is the flow through the cavity which is associated with vortex currents and tends to obstruct the primary flow. The geometric shape of the cavity is varied to study its effect on the vortex and resultant leakage flow through the seals. The curvatures of the seal and the distance of the seal tip to the end of the seal are the main parameters considered to arrive at the desired cavity which helps to create the required whirling action and to reduce the velocity of the leakage flow. Gambit software is used for modeling the geometry and Fluent software is used for the analysis. Axi-symmetric pressure based analysis is carried out using the standard κ-ε turbulence. The results of the standard cavity are compared with different variants. The flow velocity and mass flow is studied at different locations of the seal. The results indicate that by optimizing the shape of the seal cavity, the leakage through the labyrinth seal can be reduced.

Effects Of Dimple Depth on Channel Nusselt Numbers and Friction Factors

2004 ◽  
Vol 127 (8) ◽  
pp. 839-847 ◽  
Author(s):  
N. K. Burgess ◽  
P. M. Ligrani
Keyword(s):  
Reynolds Number ◽  
Nusselt Number ◽  
Local Nusselt Number ◽  
Reynolds Numbers ◽  
Secondary Flows ◽  
Channel Height ◽  
Stagnation Temperature ◽  
Nusselt Numbers ◽  
Number Ratio ◽  
Friction Factors

Experimental results, measured on dimpled test surfaces placed on one wall of different rectangular channels, are given for a ratio of air inlet stagnation temperature to surface temperature of approximately 0.94, and Reynolds numbers based on channel height from 9940 to 74,800. The data presented include friction factors, local Nusselt numbers, spatially averaged Nusselt numbers, and globally averaged Nusselt numbers. The ratios of dimple depth to dimple print diameter δ∕D are 0.1, 0.2, and 0.3 to provide information on the influences of dimple depth. The ratio of channel height to dimple print diameter is 1.00. At all Reynolds numbers considered, local spatially resolved and spatially averaged Nusselt number augmentations increase as dimple depth increases (and all other experimental and geometric parameters are held approximately constant). These are attributed to (i) increases in the strengths and intensity of vortices and associated secondary flows ejected from the dimples, as well as (ii) increases in the magnitudes of three-dimensional turbulence production and turbulence transport. The effects of these phenomena are especially apparent in local Nusselt number ratio distributions measured just inside of the dimples and just downstream of the downstream edges of the dimples. Data are also presented to illustrate the effects of Reynolds number and streamwise development for δ∕D=0.1 dimples. Significant local Nusselt number ratio variations are observed at different streamwise locations, whereas variations with the Reynolds number are mostly apparent on flat surfaces just downstream of individual dimples.

Global stability of multiple solutions in plane sudden-expansion flow

2012 ◽  
Vol 702 ◽  
pp. 378-402 ◽  
Author(s):  
Daniel Lanzerstorfer ◽  
Hendrik C. Kuhlmann
Keyword(s):  
Secondary Flow ◽  
Mirror Symmetry ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Expansion Ratio ◽  
Secondary Flows ◽  
Sudden Expansion ◽  
Shear Stresses ◽  
Two Dimensional ◽  
Large Expansion

AbstractThe two-dimensional, incompressible flow in a plane sudden expansion is investigated numerically for a systematic variation of the geometry, covering expansion ratios (steps-to-outlet heights) from $0. 25$ to $0. 95$. By means of a three-dimensional linear stability analysis global temporal modes are scrutinized. In a symmetric expansion the primary bifurcation is stationary and two-dimensional, breaking the mirror symmetry with respect to the mid-plane. The secondary asymmetric flow experiences a secondary instability to different three-dimensional modes, depending on the expansion ratio. For a moderately asymmetric expansion only one of the two secondary flows (the connected branch) is realized at low Reynolds numbers. Since the perturbed secondary flow does not deviate much from the symmetric secondary flow, both secondary stability boundaries are very close to each other. For very small and very large expansion ratios an asymptotic behaviour is found for suitably scaled critical Reynolds numbers and wavenumbers. Representative instabilities are analysed in detail using an a posteriori energy transfer analysis to reveal the physical nature of the instabilities. Depending on the geometry, pure centrifugal and elliptical amplification processes are identified. We also find that the basic flow can become unstable due to the effects of flow deceleration, streamline convergence and high shear stresses, respectively.

scholarly journals Secondary Flow and Endwall Optimization of a Transonic Turbine

Energies ◽  
2019 ◽  
Vol 12 (21) ◽  
pp. 4103 ◽  
Author(s):  
Abdul Rehman ◽  
Bo Liu ◽  
Muhammad Afzaal Asghar
Keyword(s):  
Secondary Flow ◽  
Secondary Flows ◽  
Nsga Ii ◽  
Flow Solver ◽  
Design Variables ◽  
Flow Through ◽  
Transonic Turbine ◽  
The Individual ◽  
Automated Optimization ◽  
Isentropic Efficiency

A detailed numerical analysis of secondary flows in a transonic turbine is presented in this paper. The turbine stage is optimized by mitigating secondary flow through the method of non-axisymmetric endwall design. An automated optimization platform of NUMECA/Design3D was coupled with Euranus as a flow solver for the numerical investigation. The contoured endwalls of the stator and the rotor hub were designed based on equidistant Bézier curves along the camber line in the blade channel. The initial design samples were ten times the number of the design variables, and were generated through the LHS method for database generation. The optimization of the endwalls was achieved by using a state-of-the-art multi-objective optimization algorithm, NSGA-II, connected with the BPNN to increase the isentropic efficiency and decrease the secondary kinetic energy, while the mass flow and the degree of reaction were constrained to remain on the datum value as in the original geometry. The individual optimization of the hub endwalls of the stator and the rotor produced an increase in the efficiency of 0.27% and 0.25%, respectively, resulting in a cumulative improvement of 0.46% in the efficiency. The increase in the performance was analyzed at part-load conditions, and it was further confirmed through unsteady simulations.

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