Two-dimensional separation on 25°-ramp is studied experimentally in closed-loop wind tunnel. The analysis of the flow conditions and the separation is based on wall pressure distribution, velocity fields obtained by 2D-2C PIV measurements, and velocity profiles obtained by 2C LDV measurements. The boundary layer upstream and downstream the ramp is characterized. To control the longitudinal pressure gradient, a trailing edge flap is used and the flap angle effects are studied. When the flap angle is equal to +7.5°, the flow around leading edge is symmetric, but the separation is 3D. For the case where the flap is not slanted (0°), the separation is 2D. Proper orthogonal decomposition is used to characterize the separation unsteadiness.