# Flow and Heat Transfer Characteristics of Surface-Mounted Cylinder in Presence of Rectangular Winglet Pair

## Abstract

Heat transfer and flow field characteristics past surface-mounted finite height circular cylinder in the presence of vortex generators (VGs) have been investigated numerically. Aspect ratio of circular cylinder such that the ratio of height to diameter of cylinder is kept fixed as 2.0 and Reynolds number based on diameter of cylinder and free stream velocity has been varied in the range from 1000 to 4000. Vortex generators in the form of rectangular winglet pair (RWP) in common flow down configuration with an angle of attack equal to 35° are considered for the present study. Present study aims to investigate the effect of combination of finite height cylinder and RWP on heat transfer enhancement by varying location of RWP relative to center of the cylinder. To illustrate the behavior of flow field, streamlines plots have been used and are compared with heat transfer field by using temperature contours. Pressure loss and heat transfer enhancement are quantified in terms of friction factor and overall surface-averaged Nusselt number, respectively. The concept of secondary flow intensity has been used to estimate the relationship between heat transfer and secondary flow. Effect of RWP location on thermal performance factor has also been reported.

## Keywords

Finite height cylinder Rectangular winglet pair Secondary flow intensity Nusselt number## Nomenclature

*A*Area of the heated surface

*C*_{p}Coefficient of pressure

*D*Cylinder diameter

*f*Friction factor

*H*Cylinder height

*h*Convective heat transfer coefficient

*h*_{VG}Height of vortex generator

- JF
Thermal performance factor

*k*Turbulent kinetic energy

*L*_{1}Length of computational domain

*L*_{2}Width of computational domain

*L*_{3}Height of computationaldomain

*l*_{VG}Length of vortex generator

*Nu*Nusselt number

*P*Non-dimensional pressure

*Re*Reynolds number

- Se
Secondary flow intensity

*T*Temperature

- \(U_{\infty }\)
Free stream velocity

- \(U_{j}\)
Cartesian velocity component in \(X_{j}\)-coordinate direction

- \(X_{j}\)
Non-dimensionalized Cartesian space coordinates in

*X*,*Y*,*Z*direction*X*,*Y*,*Z*Non-dimensionalized Cartesian space coordinates

## Greek symbols

- \(\alpha_{\text{t}}\)
Turbulent dynamic thermal diffusivity

- \(\beta\)
Angle of attack of vortex generator

- \(\Delta X\)
Streamwise center distance between tube and winglet

- \(\Delta Y\)
Spanwise center distance between tube and winglet

- \(\varepsilon\)
Dissipation rate

- \(\lambda\)
Thermal conductivity

- \(\nu\)
Kinematic viscosity of fluid

- \(\nu_{\text{t}}\)
Turbulent kinematic viscosity of fluid

- \(\Omega\)
Volume of the computational domain

- \(\omega^{\text{n}}\)
Vorticity component normal to a cross section

- \(\rho\)
Density of fluid

- \(\sigma_{k}\)
Turbulent Prandtl numbers for

*k*- \(\sigma_{\varepsilon }\)
Turbulent Prandtl numbers for \(\varepsilon\)

- \(\theta\)
Non-dimensional temperature

- \(y^{ + }\)
Wall

*y*-plus

## Subscripts

- b
Bulk-mean value

- \(\infty\)
Inlet

- local
Local value

- n
Normal direction

- o
Absence of vortex generator

- w
Wall

## Abbreviations

- AR
Aspect ratio

- CFD
Common flow down

- CFU
Common flow up

- DWP
Delta winglet pair

- FFR
Friction factor ratio

- HTR
Heat transfer ratio

- RWP
Rectangular winglet pair

- SFIR
Secondary flow intensity ratio

- VG
Vortex generator

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