Modern aircraft adopt swept wings to reduce wave drag associated with shock waves. Three-dimensional boundary layer on the swept wing makes crossflow instability dominant near the leading edge. Therefore, small disturbances can easily promote the instability and eventually trigger turbulent transition. Disturbances are classified into stationary waves, which exhibit no temporal variation, and traveling waves, which vary in time. Under conditions with high turbulence intensity in the freestream, such as in high-disturbance wind tunnels, traveling waves become dominant in the flow transition [1]. Harmonic waves are known to be excited when stationary and traveling waves coexist [2]. However, the influence of freestream turbulence on wind-tunnel experiments remains insufficiently understood. Accordingly, we aim to elucidate the effects of stationary and traveling waves induced by surface roughness and freestream turbulence on the flow transition over a natural laminar flow wing. We consider the NLF(2)-0415 airfoil under a low-Reynolds-number condition (O(106)) representative of a wind-tunnel environment, with an infinite swept-wing approximation applied. We employ stability analyses based on linear parabolized stability equations to determine the N-factor and the most unstable wavelengths. In addition, direct numerical simulation (DNS) and nonlinear parabolized stability equations (NPSE) are combined to examine the development of disturbances with the most unstable wavelengths, as shown in Fig. 1. Specifically, DNS is performed to mimic the receptivity of the disturbance from roughness or freestream turbulence near the leading edge, and the resulting amplitudes were used as initial amplitudes for NPSE transition-point analysis. Our analysis revealed that the unstable frequencies of traveling waves are lower than those of stationary waves, and that for the NLF(2)-0415 airfoil, crossflow vortices may decay before reaching saturation and breakdown. We will discuss transition points for stationary and traveling waves and their mutual interaction.