Flow control with plasma discharge is one of the promising techniques for the futuristic aerodynamic control methods. In the present work, a hypersonic flow control method which utilizes a direct-current (DC) arc plasma discharge is investigated as a fundamental study on such a new device. Hypersonic wind tunnel experiments were conducted to measure the effect of the discharge on Mach-7 flow over a compression and a expansion corner. The experimental results showed that, in the case of the expansion corner, a large pressure fall induced by the plasma discharge was observed. However, the change in the entire flow field such as shock wave formation was not clear. In the case of the compression corner, the boundary separation at the corner is enhanced and enlarged by the discharge, causing the pressure to change near the plasma area. Numerical analyses were conducted on both of these cases to understand the mechanisms of the observed phenomena. Park's two temperature model and Gupta's 11-species model were employed to describe the plasma flow. In order to simulate the effects of the plasma, a simple energy addition model is proposed, where the discharge effect is replaced by an energy addition to both the translational-rotational and the vibrational-electron-excitation energy modes. The numerical results based on the proposed model successfully showed a good qualitative agreement with the experimental results for the nitrogen molecular light emission. It was revealed that the present idea of utilizing the DC arc discharge as a flow control method is more effective in manipulating the flow when it is applied to a compression corner.