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244  5. Some worked examples arising from physical problems



          finite plate.) By virtue of the existence of a stream function, we see that we must also
          scale      we  write




          and then we must choose       to give








          This  set  is to be solved,  subject to  the boundary  conditions (5.110c,d), written in
          boundary-layer variables, and  matching  conditions for   The  leading-order
          problem (zero subscripts) satisfies





          with

          and the matching conditions





            To solve equations (5.111), we note, first, that   and then the matching
          condition requires   throughout this region. Next we use (5.111c) to allow the
          introduction of a stream function              and then (5.111a) can be
          written


          with

          and


          The relevant solution (Blasius,  1908)  takes a similarity form:
                           direct substitution then yields the ordinary differential equation
          for


          with

          This  equation must be  solved numerically;  the properties  of the solution  agree well
          with experimental data for laminar flows. It is left as an exercise to show that there are
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