INVESTIGATION ON SURFACE ROUGHNESS EFFECT FOR TURBULENT FLOW IN A RECTANGULAR DUCT

Abstract

The effect of surface roughness on turbulence intensity, friction factor and velocity distribution in a rectangular duct with bottom wall having ribbed-grooved surface has been studied for a Reynolds number range of 6000 to 23000. The duct aspect ratio is kept 8.3 for the pitch ratio (p/e) of 10. Turbulence intensity, friction factor and velocity distribution in the duct are experimentally determined for both the smooth and the rough surface. Hot Wire Anemometer has been used for the measurement of turbulent intensity. Efforts are made to take the readings from ACQUIRE hardware and software system for acquiring the data, the system is not available at MIED, IIT Roorkee, hence it has been borrowed from Civil Engineering department, IIT Roorkee, but that too did not work due to improper functioning of software, therefore the readings have been taken manually with proper care. Experimental results for smooth and rough surface have been compared and it is found that, turbulence intensity increases by 19% whereas friction factor increases by 5 times for the rough surface as compared to the smooth surface. Numerical analysis is also done for the rough surface by taking k-w turbulent model. On comparison of experimental results with numerical results, turbulence intensity and velocity distribution shows good agreement, whereas friction factor gives more deviation for higher Reynolds number for the k-w turbulent model