Page 150 - 48Fundamentals of Compressible Fluid Mechanics
P. 150

112              CHAPTER 6. NORMAL SHOCK IN VARIABLE DUCT AREAS
                                                                                                              P 01
                                            The efficiency of the diffuser is defined
                                                                                       h                      P 02
                                            as the ratio of the enthalpy change that
                                                                                                              P 2
                                            occurred between the entrance to exit            0 1
                                                                                                   0 2
                                            stagnation pressure to the kinetic en-
                                                                                                   2          P 1
                                            ergy.
                                                                           (6.6)

                                                                                              1







                                                                                                          s,entropy


                                             For perfect gas equation (??) can be




                                            converted to                         Fig. 6.3: Description to clarify the definition of
                                                                                        diffuser efficiency
                                                                           (6.7)





                                             And further expanding equation (6.7) results in




                                                                                                                (6.8)





                                                    %
                                                                     %











                                                                       #
                                                     % #


                                            Example 6.3:  
         
        
          
      "


                                            A wind tunnel combined from
                                            a nozzle and a diffuser (actu-         nozzle           Diffuser
                                            ally two nozzles connected by a        1
                                            constant area see Figure (6.4))            2       3    4
                                            the required condition at point
                                                               and pres-               capacitor
                                                            and tempera-
                                                        . The cross sec-
                                            3 are:


                                            tion in area between the nuzzle           Compressor
                                            ture of

                                                                . What is
                                            area of nozzle’s throat and what                          cooler

                                            sure of 
 )(
                                            and diffuser is
                                            is area of the diffuser’s throat to

                                            maintain chocked diffuser with
                                            subsonic flow in the expansion                                heat

                                            section.       can be as-                                out
                                            sumed. Assume that a shock
                                            occors in the test section.
                                                                          Fig. 6.4: Schematic of a supersonic tunnel in a contin-
                                                                                 uous region (and also for example (6.3)
                                              SOLUTION
                                            The condition at 
  
 is summarized in following table  
   % 
 3'
 3






















                                                     
 
 

 
 
 
(  
 
!(/3 
   
 3 (
   145   146   147   148   149   150   151   152   153   154   155