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Blade and Cascade Nomenclature

 Blade and Cascade Nomenclature

  • Since airfoils are employed in accelerating and diffusing the air in a compressor, much of the theory and research concerning the flow in axial compressors are based on studies of isolated airfoils.
  •  The nomenclature and methods of describing compressor blade shapes are almost identical to that of aircraft wings. Research in axial compressors involves the intereffect of one blade on the other, thus several blades are placed in a row to simulate a compressor rotor or stator. Such a row is called a cascade.
  •  When discussing blades, all angles that describe the blade and its orientation are measured with respect to the shaft (z axis) of the compressor.
  • The airfoils are curved, convex on one side and concave on the other, with the rotor rotating toward the concave side. The concave side is called the pressure side of the blade, and the convex side is called the suction side of the blade.
  • The chordline of an airfoil is a straight line drawn from the leading edge to the trailing edge of the airfoil, and the chord is the length of the chordline .
  •  The camber line is a line drawn halfway between the two surfaces, and the distance between the camberline and the chordline is the camber of the blade. The camber angle θ is the turning angle of the camberline.
  •  The blade shape is described by specifying the ratio of the chord to the camber at some particular
  • length on the chordline, measured from the leading edge. The aspect ratio AR
  • is the ratio of the blade length to the chord length.
  • The term “hub-to-tip ratio” is used frequently instead of aspect ratio. The aspect ratio becomes important when three-dimensional flow characteristics are discussed.
  • The aspect ratio is established when the mass flow characteristics are discussed. The aspect ratio is established when the mass flow and axial velocity have been determined.

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