Centrifugal fans are machine for moving a gas, such as air, by accelerating it radiallyrnoutward in an impeller to a surrounding casing. They are often used in heating andrnventilation and air condition system (HVAC). But, the efficiency of the fan can still bernimproved by studying their detail performance characteristics and modifying theirrngeometry. rnIn this thesis, at first step, an experimental study is conducted to investigate thernperformance characteristics of forward curved centrifugal fan by varying its volume flowrnrate. From the performance characteristics of a base machine which were plotted basedrnon the test result, the performance of the fan increases as the flow rate of the workingrnfluid increases from zero to design flow rate of the fan. Beyond its design point, thernperformance of the fan starts to drop. Next, a two dimensional (2D), steady state,rnincompressible, turbulent flow field inside fan models have been analyzed numerically. rnDuring numerical simulation, from all types of k-Îµ and k-Ï‰ turbulence models, thernappropriate turbulence model is selected based on their agreement with the experimentalrnresult. Details of CFD analysis are done on the effects of shaft speed and blade numbers.rnFrom the CFD analysis, a best improvement of 4.05% in efficiency has been attained atrn49 blade number. But the analysis done on the shaft speed resulted in the flow rate andrnoutlet total pressure enhancement with direct proportion to input power and shaft speed.