3. Momentum thicknessδ(O)(动量厚度,动量损失厚度) ,= pudy. u y pua △M=0w-v △M=pUO" p8U2=p u(u-uky 0 ="= ou3. Momentum Thickness   ** ( ) （动量厚度，动量损失厚度） y d U u ( )   = −   0 2 M Uu u dy  udy u    0  udy U   0 M U U **  =    U u(U u)dy  = −    0 ** 2 dy U u U u        = = −    0 ** 1 M  real = M  ideal =