Gobyzov O.A.   Markovich D.M.   Lozhkin Y.A.   Ivanov I.E.   Filippov S.Y.   Krasilnikov A.V.   Kozlovskiy V.A.   Lipnitskiy Y.M.   Ganiev Y.H.  

PIV measurements of nonuniform supersonic flow in continuous-operated wind tunnel

Reporter: Gobyzov O.A.

In the paper an experimental results of planar PIV study of stationary rarified supersonic flow with discontinuities are presented and analyzed. Experiments were carried out in theTsNIIMash «U-4M» continuous operated supersonic wind tunnel [1] at Mach number 3 and 4. PIV and PTV advantages and drawbacks in case of investigation of supersonic flow with complex shockwave structure are considered in the paper. Particular features of the experimental technique, including hardware requirements, flow seeding and image quality for that case, as well as the image and data processing methods are considered. Experimental data is supplemented by numerical simulation.
  PIV-measurements of a free supersonic flow in the test section of a wind tunnel at Mach number M=3 provided a spatial distribution of streamwise and transversal components of the flow velocity, allowed to estimate flow skewness and nonuniformity, and to reveal flow disturbances propagating from the upstream area. 
  An experimental study of a converging oblique shock wave interaction, supplemented by numerical simulation data was performed in the same wind tunnel at M=4.A converging oblique shock wave configuration was generated by axisymmetric conical «mock nozzles» of 5° and 10° cone angle, introduced into the flow.
  Velocity distributions for both cone angles were retrieved from particle images. As it was expected, no evidences of irregular shock wave interaction were observed in case of 5°nozzle, while in case of 10° nozzle a downstream contact discontinuity, specific for the Mach interaction [2], was detected (Fig. 2), although a Mach stem was not clearly visible. The PIV data acquired in experiments were compared with the conventional schlieren visualization results and numerical simulation data.
  Results obtained in the experiments have confirmed that particle-based velocity measurements are capable of delivering quantitative velocity distribution for complex supersonic flows with discontinuities and can faithfully represent the large-scale structure of the flow. At the same time, small-scale features of the flow can be strongly distorted or even missed due to the lack of spatial resolution of the method or, especially for rarified flows – to the dynamic characteristics of seeding particles [3, 4].

1. Czajkowski E. Russian aeronautical test facilities // Anser Center for International Aerospace Cooperation, 1994
2. Kutler, P. and Sakell, L., Two-Dimensional, Shock-on-Shock Interaction
Problem // AIMA Journal, Vol. 13, No. 3, p. 361-367, 1975
3. Ragni D.,• Schrijer F., van Oudheusden• B. W.,  • Scarano F. Particle tracer response across shocks measured by PIV// Exp. Fluids,  vol. 50,  p. 53–64, 2011
4. Tedeschi G., Gouin H., Elena M. Motion of tracer particles in supersonic flows //Exp. Fluids vol. 26, p. 288-296, 1999

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