# Fluid flow and heat transfer characteristics for a square prism (blockage ratio = 0.1) placed inside a wind tunnel

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## Abstract

Experimental investigations in fluid flow and heat transfer have been carried out to study the effect of wall proximity due to flow separation around a square prism at Reynolds number 2.6 × 10^{4}, blockage ratio 0.1, different height-ratios and various angles of attack. The static pressure distribution has been measured on all faces of the square prism. The results have been presented in the form of pressure coefficient, drag coefficient for various height-ratios. The pressure distribution shows positive values on the front face whereas on the rear face negative values of the pressure coefficient have been observed. The positive pressure coefficient for different height-ratios does not vary too much but the negative values of pressure coefficient are higher for all points on the surface as the bluff body approaches towards the upper wall of the wind tunnel. The drag coefficient decreases with the increase in angle of attack as the height-ratio decreases. The maximum value of drag coefficient has been observed at an angle of attack nearly 50° for the square prism at all height-ratios. The heat transfer experiments have been carried out under constant heat flux condition. Heat transfer coefficient are determined from the measured wall temperature and ambient temperature and presented in the form of Nusselt number. Both local and average Nusselt numbers have been presented for various height-ratios. The variation of local Nusselt number has been shown with non-dimensional distance for different angles of attack. The variation of average Nusselt number has also been shown with different angles of attack. The local as well as average Nusselt number decreases as the height-ratio decreases for all non-dimensional distance and angle of attack, respectively, for the square prism. The average Nusselt number for the square prism varies with the angle of attack. But there is no definite angle of attack at which the value of average Nusselt number is either maximum or minimum.

## Keywords

Nusselt Number Wind Tunnel Drag Coefficient Pressure Coefficient Local Nusselt Number## List of symbols

*a*side length of the square prism, mm

*a*/*H*blockage ratio of the square prism, a non-dimensional number

*A*surface area of the bluff body, m

^{2}*A*_{h}heating foil surface area, m

^{2}*C*_{D}drag coefficient =

*F*_{D}/(0.5*ρ*_{ a }*u*^{2}*A*)*C*_{p}pressure coefficient = (

*p*−*p*_{ a })/(0.5*ρ*_{ a }*u*^{2})*F*_{D}drag force, N

*h*_{x}local heat transfer coefficient, W/m

^{2}K*h*_{a}average heat transfer coefficient, W/m

^{2}K*H*height of the wind tunnel, mm

*I*current, A

*k*thermal conductivity, W/m K

*Nu*_{x}local Nusselt number, (

*h*_{x}*a*/*k*)*Nu*_{a}average Nusselt number (

*h*_{a}*a*/*k*)*p*static pressure, mm of water

*p*_{a}ambient pressure, mm of water

*Pr*Prandtl number

*q*heat flux, W/m

^{2}*Re*Reynolds number based on the velocity of air and the characteristics length of the bluff body = (

*u**a*/*ν*_{a})*T*_{a}ambient temperature, K

*T*_{x}local wall temperature, K

- Δ
*T* difference between local wall temperature and ambient temperature, K

*u*velocity of air, m/s

*V*voltage, V

*w*uncertainty

*x*distance from the edge of the prism, mm

*x*/*a*non-dimensional distance for the square prism

*y*distance of the centroid of the bluff body from the upper wall of the wind tunnel

*y*/*H*height-ratio, a non-dimensional number

*α*angle of attack, degrees

*β*coefficient of thermal expansion, K

^{−1}*ρ*_{a}density of air, kg/m

^{3}*ρ*_{w}density of water, kg/m

^{3}*μ*_{a}dynamic viscosity of air, N s/m

^{2}*ν*_{a}kinematic viscosity of air, m

^{2}/s

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