问答题 (清华大学2006—2007学年春季学期期中考试试题)Giyen the steady，incompressible velocity distribution V=x+y)i+C(x+y)j+0k，where C is a constant，if conservation of mass is satisfied，find the value of C．Write down the strain rate tensor S _ij =0．5(u _ij +u _ji )and the vorticity vector(▽×V)．