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Effect of Porosity and Transverse Magnetic Field on the Wake Separation and Detachment around a Porous Square Cylinder

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Abstract

Porosity plays a significant role in controlling the wake dynamics behind a porous object. A porous object allows fluid to flow through it partially, which causes a reduction in the size of the wake behind the body. The wake dynamics can also be controlled by imposing an external magnetic field on an electrically conducting fluid. Keeping in view the above facts, numerical computations are performed to explore the coupled effect of the porosity and the magnetic field on the wake dynamics around a porous square cylinder. The cylinder is placed in a two-dimensional unconfined domain having a fictitious blockage ratio of 0.025. The Reynolds number is kept in the range 10–40 with Darcy number 10−6–10−2 and Hartmann number 0–8. The flow in the porous medium is modeled using the Darcy–Brinkman–Forchheimer model. The critical magnetic parameter for the complete suppression of the wake behind the cylinder for the given range of Darcy and Reynolds numbers is computed. The results show that the critical Hartmann number increases with the Reynolds number, whereas it decreases with the Darcy number. Another interesting finding is the estimation of the critical Hartmann number for the detachment of the recirculation region from the rear surface of the cylinder. The detachment Hartmann number increases with an increase in the Reynolds number and a decrease in the Darcy number.

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Abbreviations

B :

Blockage ratio \(\left( { = D{/}H} \right)\)

B 0 :

Magnetic field intensity (T)

\(\overrightarrow {B}\) :

Magnetic field vector

C D :

Drag coefficient

\(d_{{\text{p}}}\) :

Characteristics diameter of particle (m)

D :

Cylinder size (m)

Da:

Darcy number \(\left( {{{ = K} \mathord{\left/ {\vphantom {{ = K} {D^{2} }}} \right. \kern-\nulldelimiterspace} {D^{2} }}} \right)\)

F Lorentz :

Lorentz force (N)

H :

Width of computational domain (m)

Ha:

Hartmann number \(\left( { = B_{0} D\sqrt {{\sigma \mathord{\left/ {\vphantom {\sigma {\rho \eta }}} \right. \kern-\nulldelimiterspace} {\rho \eta }}} } \right)\)

J :

Current density (amp/m2)

K :

Permeability (m2)

L :

Length of computational domain (m)

L d :

Downstream length (m)

L r :

Dimensionless bubble length \(\left( {{{ = \overline{{L_{r} }} } \mathord{\left/ {\vphantom {{ = \overline{{L_{r} }} } D}} \right. \kern-\nulldelimiterspace} D}} \right)\)

L u :

Upstream length (m)

N :

Stuart number \(\left( { = {{{\text{Ha}}^{2} } \mathord{\left/ {\vphantom {{{\text{Ha}}^{2} } {\text{Re}}}} \right. \kern-\nulldelimiterspace} {\text{Re}}}} \right)\)

p :

Dimensionless pressure \(\left( { = {{\overline{p} } \mathord{\left/ {\vphantom {{\overline{p} } {\rho \,u_{\infty }^{2} }}} \right. \kern-\nulldelimiterspace} {\rho \,u_{\infty }^{2} }}} \right)\)

Pr:

Prandtl number \(\left( { = {\eta \mathord{\left/ {\vphantom {\eta \alpha }} \right. \kern-\nulldelimiterspace} \alpha }} \right)\)

Re:

Reynolds number \(\left( { = {{u_{\infty } D} \mathord{\left/ {\vphantom {{u_{\infty } D} \eta }} \right. \kern-\nulldelimiterspace} \eta }} \right)\)

\(u_{\infty }\) :

Freestream velocity (m/s)

u :

Dimensionless axial velocity \(\left( { = {{\overline{u} } \mathord{\left/ {\vphantom {{\overline{u} } {u_{\infty } }}} \right. \kern-\nulldelimiterspace} {u_{\infty } }}} \right)\)

\(\overrightarrow {V}\) :

Velocity vector (m/s)

v :

Dimensionless normal velocity \(\left( { = {{\overline{v} } \mathord{\left/ {\vphantom {{\overline{v} } {u_{\infty } }}} \right. \kern-\nulldelimiterspace} {u_{\infty } }}} \right)\)

\(v\) :

Darcy velocity (m/s)

x :

Dimensionless axial coordinate \(\left( { = {{\overline{x} } \mathord{\left/ {\vphantom {{\overline{x} } D}} \right. \kern-\nulldelimiterspace} D}} \right)\)

y :

Dimensionless normal coordinate \(\left( { = {{\overline{y} } \mathord{\left/ {\vphantom {{\overline{y} } D}} \right. \kern-\nulldelimiterspace} D}} \right)\)

\(\alpha\) :

Thermal diffusivity of fluid (m2/s)

ε :

Porosity

\(\Lambda\) :

Viscosity ratio (= \({{\mu_{{\text{e}}} } \mathord{\left/ {\vphantom {{\mu_{{\text{e}}} } \mu }} \right. \kern-\nulldelimiterspace} \mu }\))

\(\eta\) :

Kinematic viscosity of fluid (m2/s)

\(\mu\) :

Dynamic viscosity of fluid (Pa s)

\(\rho\) :

Density of fluid (kg/m3)

\(\sigma\) :

Electrical conductivity of fluid (S/m)

:

Freestream

e:

Effective

–:

Dimensional quantity

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DC contributed to conceptualization and writing—review and editing; CK and BM contributed to methodology, formal analysis and investigation; CK contributed to writing—original draft preparation; DC and BM supervised the study.

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Correspondence to Dipankar Chatterjee.

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Kumar, C., Chatterjee, D. & Mondal, B. Effect of Porosity and Transverse Magnetic Field on the Wake Separation and Detachment around a Porous Square Cylinder. Transp Porous Med 146, 805–825 (2023). https://doi.org/10.1007/s11242-022-01889-y

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  • DOI: https://doi.org/10.1007/s11242-022-01889-y

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