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CFD investigation on the offset ratio effect on thermal characteristics of a combined wall and offset jets flow

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Abstract

The present paper deals with CFD simulation of a two-dimensional, steady, incompressible and turbulent flow combining a wall jet and an offset jet (this combination will be denoted wall offset jet) in order to study the heat transfer phenomenon in this type of flow. Several turbulence models were tested including standard k–ω, SST k–ω, standard k–ε, RNG k–ε and realizable k–ε models. A parametric study was also presented to investigate the offset ratio H and the Reynolds number Re effect on the local (Nu) and average \( \left( {\overline{{\text{Nu}}} } \right) \) Nusselt number evolution along the wall. Constant wall heat flux boundary condition is considered. The Reynolds number and the offset ratio have been varied respectively from 10,000 to 40,000 and from 5 to 20 and Pr = 0.7 is adopted for all computation. Correlations that predict the average Nusselt number as a function of both the offset ratio H and the Reynolds number Re are also provided. This study has allowed us to conclude that the heat transfer exchanged between the flow and the wall is intensified when decreasing the offset ratio H and increasing the Reynolds number Re.

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Abbreviations

d:

Nozzle width (m)

e:

Grid expansion ratio

h:

Offset ratio (m)

H:

Dimensionless offset ratio H = h/d

I:

Turbulence intensity (%)

k:

Turbulent kinetic energy (m2/s2)

K:

Dimensionless turbulent kinetic energy K = k/u 20

l:

Nozzle length (m)

L:

Horizontal wall length (m)

Nu:

Local Nusselt number \( \text{Nu} = \frac{{{\tilde{\text{h}}} \times \text{d}}}{\uplambda} \)

\( \overline{{\text{Nu}}} \) :

Average Nusselt number

p:

Static pressure (Pa)

P:

Dimensionless static pressure \( {\text{P}} = \frac{{{\text{p}} - {\text{p}}_{\text{a}} }}{{\uprho{\text{u}}_{0}^{2} }} \)

Re:

Reynolds number \( \text{Re} = \frac{{\text{u}_{0} \times \text{d}}}{\upupsilon} \)

s:

Grid spacing

u:

Longitudinal velocity (m/s)

U:

Dimensionless longitudinal velocity U = u/u0

x:

Longitudinal coordinates (along x axis) (m)

X:

Dimensionless longitudinal coordinates X = x/d

y:

Transverse coordinates (along y axis) (m)

Y:

Dimensionless transverse coordinates Y = y/d

\( \tilde{\text{h}} \) :

Heat transfer coefficient (w/m2 k) \( {\tilde{\text{h}}} = \frac{{\text{q}_{\text{w}} }}{{\text{T}_{\text{w}} - \text{T}_{\text{a}} }} \)

v:

Transverse velocity (m/s)

V:

Dimensionless transverse velocity V = v/u0

\( \upmu \) :

Dynamic viscosity (kg/m s)

\( \upupsilon \) :

Kinematic viscosity (m2/s)

\( \uprho \) :

Fluid density (kg/m3)

\( \uplambda \) :

Thermal conductivity (w/m k)

ω:

Specific dissipation rate of k (1/s)

0:

Initial value (at the nozzle exit)

a:

Ambient value

max:

Maximum value

t:

Turbulent value

w:

Wall value

WOJ:

Combined wall and offset jet flow

FPJ:

Free parallel jets

LWJ:

Lower wall jet

UOJ:

Upper offset jet

SOJ:

Single offset jet flow

UVC:

Upper vortex center

LVC:

Lower vortex center

MP:

Merge point

CP:

Combined point

\( \text{conv} \) :

Converging zone

\( \text{merg} \) :

Merging zone

\( \text{comb} \) :

Combined zone

\( {\text{all.zone}} \) :

Along the whole WOJ zone

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Authors and Affiliations

  1. Unit of Metrology and Energy Systems, National Engineering School of Monastir, Avenue Ibn El Jazzar, 5019, Monastir, Tunisia

    Nidhal Hnaien, Salwa Marzouk & Habib Ben Aissia

  2. Thermal Center of Lyon (CETHIL - UMR CNRS 5008), INSA, Lyon, France

    Jacques Jay

Authors
  1. Nidhal Hnaien
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  2. Salwa Marzouk
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  3. Habib Ben Aissia
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  4. Jacques Jay
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Correspondence to Nidhal Hnaien.

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Hnaien, N., Marzouk, S., Ben Aissia, H. et al. CFD investigation on the offset ratio effect on thermal characteristics of a combined wall and offset jets flow. Heat Mass Transfer 53, 2531–2549 (2017). https://doi.org/10.1007/s00231-017-2000-0

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  • DOI: https://doi.org/10.1007/s00231-017-2000-0

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