A CFD numerical investigations of air flow and temperature distribution in data centers is presented for different operating and geometric conditions. Numerical experiments were conducted to parametrically study the effects of perforated tiles opening ratio, data center power density and locations of Computer Room Air Conditioning (CRAC) on the data center performance. Temperature distribution especially hot spot points, air flow characteristics particularly air recirculation and bypass and thermal management in data centers are evaluated in terms of the measureable overall performance parameters: supply/return heat indices (SHI/RHI), return temperature indices (RTI) and return cooling indices (RCI). Techniques of using cold aisle containments for enhancing the cooling effectiveness of data centers is investigated and evaluated. The results showed that (i) increasing the perforation ratio of perforated tails decreases the recirculation and bypass of air flow around the rack (ii) increasing data centers power density and supplied air flow rates increases the air bypass and air re-circulation, (iii) changing the spacing between the CRAC units and cold aisle slightly changes of air recirculation and bypass around the racks, and (iv) using appropriate cold aisle containment improves the performance of cooling of data centers, especially at high power density