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Experimental Investigation of Pressure Distribution in the Wind Tunnel Contarection and Preventation of Probable Separation

Mirzaei, Mohsen | 2008

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 39227 (45)
  4. University: Sharif University of Technology
  5. Department: Aerospace Engineering
  6. Advisor(s): Soltani, Mohammad Reza
  7. Abstract:
  8. Contraction sections are an integral part of all wind tunnels, whether designed for basic fluid flow research or model testing. The location of the contraction, just upstream of the test section, makes it very important to achieve a high quality contraction design. The effect of a contraction on unsteady velocity variations is significant to increase the mean velocity. Furthermore, contraction has a suitable role on the turbulence reduction in a wind tunnel. The contraction itself further reduces the turbulence in terms of percentage of the wind speed. This is due to the increase of the wind speed by a factor equal to the contraction ratio. In this research, to investigation flow quality in a subsonic wind tunnel, pressure distribution along the contraction has been studied. It is seen that the pressure distribution along the contraction is not favorable and adverse pressure distribution occur at two positions; at inlet and outlet of the contraction. These adverse pressure gradients which indicate flow instability in the contraction, cab be controlled by gluing trip strip near the adverse positions. In the next stage, subsonic wind tunnel experiments were conducted to study the effect of tripped boundary layer on the pressure distribution in the contraction region of the tunnel. Measurements were performed by installing trip strip at four different positions in the convex portion and one position in the concave portion of the contraction. The results show that installation of the trip strips, have significant effects on the pressure distribution in the contraction and eventually on turbulence intensity in the test section. The reduction in the free stream turbulence and reduction of the wall static pressure distribution deferred signified with the location of the trip strip but for all cases trip strip causes adverse pressure gradient move to the upstream, then flow have more time and distance to be uniform at the test section. The results show that the trip strip at X/L=0.79; 54 cm near the test section, has the best effect on the pressure distribution and turbulence intensity. Of course, trip strip at X/L=0.115, in the concave portion of contraction has significant effect on the pressure distribution and turbulence intensity as well as the X/L=0.79.After finding optimum position for trip strip, the effect of trip height on flow behavior is investigated. For this, trip strips with three different diameters are installed in the optimum position. The results show that the heights of trip strips haven't important effect on the pressure distribution in the inlet of contraction but have significant effect on the outlet pressure distribution. The trip strip with 0.91 mm in diameter has the best effect on the pressure distribution.
  9. Keywords:
  10. Pressure Distribution ; Trip Strip ; Contraction ; Adverse Gradient

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