Tham khảo tài liệu 'wind tunnels and experimental fluid dynamics research part 7', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 228 Wind Tunnelsand Experimental Fluid Dynamics Research Following some of the ideas exposed by Tang et al 2007 we selected two upstream points one on the upper surface and the other on the lower surface see Experimental procedure to analyze the pressure time history. Our pressure taps were located at the x position being the flap location at . Such pressure taps were designated Up for upper surface and Low for lower surface . The main difference regarding the procedure followed by Tang et al 20 was our election of the pressure taps location upstream the perturbation device flap location. Figures 37a and 37b show the Cp time history for 5 angle of attack AOA and 22Hz and 38Hz oscillating frequencies respectively. Figures 37c and 37d are for those two frequencies but for 11 of angle of attack. Figure 37a shows some irregularities in the pressure fluctuations than Figure 37b. It seems that as frequency grow the pressure fluctuations become similar in amplitude both in the upper and lower surfaces. The difference between those times histories could be associated with the changes in the near wake as the frequency grows see Figure 33 . Although velocities spectra showed in Figure 12 corresponds to 0 of angle of attack we could made a comparison between such results and the pressure time histories for 5 angle of attack bearing in mind the similar qualitative behavior of the airfoil for 0 and 5 angles of attack. Moreover such times history behavior is also associated with the pair of vortex structures in the near wake described above regarding Figures 34 and 35 . Cpvs. Time-Gurney-22 Hz. - DA . . Up Lo w WlMIIHffl 1111 1 Lil WT LII 1 LLU 11 11II I LimJiIII J I l Illi III Illi L I fl II lit w rif 1IIITI1 1 ryi 1 r tHt Time sec. Cpvs. Time-Gurney-38 Hz - WA Up Low Time sec. Fig. 37. Cp vs. time Low Speed Turbulent Boundary Layer Wind Tunnels 229 If we observe carefully for the same angle of attack and far away from the stall as frequency grow the upper Cp becomes
