Comment on “Unsteady stagnation-point flow over a plate moving along the direction of flow impingement” by Y. Zhong and T. Fang, Int. J. Heat Mass Transfer, 54 (2011) 3103–3108

It is shown that the title problem discussed recently by Zhong and Fang is equivalent to the classical unsteady stagnation flow problem with a “hyperbolic time variation” of the free stream velocity considered more than 50 years ago by K.T. Yang. The (formal) difference between the two approaches lies in the fact that in Yang’s paper the governing equations have been written in the body-centered coordinate system, while in Zhong and Fang’s paper the laboratory frame has been used. Consequently, the pertinent boundary-value problem of Zhong and Fang can be mapped onto that of Yang by simple translations of the similarity dependent and independent variables image and image.