In gas-turbine engines, a low-pressure turbine (LPT) powers the fan. It typically weighs about one-third of the total engine weight. The design of a lightweight engine calls for curtailing the LPT weight, which implies a reduction in the blade count without compromising on the isentropic efficiency. This gave rise to the philosophy of ultra high-lift blade designs, with increased blade loading. However, such designs suffer from higher performance penalties compared to conventional turbine blades. The ultra-high lift blade profiles suffer from flow losses due to severe adverse pressure gradient-induced flow separation, particularly at low Reynolds numbers encountered during the cruise. Nevertheless, the losses could be reduced by carefully controlling the laminar to turbulent transition over the suction surface of the blades. The existing unsteady mechanisms in the LPT environment such as the free-stream turbulence and periodically shed wakes by upstream blade rows are effective only to a certain extent in reducing the separation bubble-related losses. Passive flow control strategies such as surface roughness eliminate the bubble entirely but increase the turbulent wetted area. The benefit gained due to the suppression of the bubble is eclipsed by an increase in the drag due to the turbulent boundary layer. We intend to reduce this additional drag by employing surface protrusions like Riblets, whose drag-reducing performance in the turbulent regime under zero pressure gradients. In this thesis, the performance of riblets under turbine-type adverse pressure gradients will be explored. In particular, the aim will be to employ surface roughness in the transitional regime to eliminate the separation bubble and utilize riblets in the turbulent regime to reduce the viscous drag and turbulent wetted area. Thus it is expected to propose a new blade design – ‘roughened ultra high-lift blade with grooves’, that could offer superior performance compared to the smooth surface blade designs currently employed by the industry.