Abstract
Steady oblique shock waves are observed for the first time in non-ideal supersonic flows of single-phase organic vapors. A diamond-shaped airfoil with semi-aperture 7.5^{circ } at the leading edge and 10^{circ } at the trailing edge is placed within a uniform supersonic stream (Mach number M = 1.5) of siloxane fluid MDM (octamethyltrisiloxane, hbox {C}_8hbox {H}_{24}hbox {O}_2hbox {Si}_3). Oblique shock waves are observed at varying stagnation conditions in the pre-shock state, for a set of flow deviation angles obtained by changing the attitude of the model with respect to the wind tunnel axis. Stagnation temperatures and pressures reduced by critical values range from 0.928 to 0.979 and from 0.200 to 0.615, respectively. Oblique shock waves are characterized through independent measurements of pressure, temperature and Mach number. Stagnation pressure and temperature are measured in the wind-tunnel settling chamber, while the pre-shock, post-shock and post-expansion static pressures are measured at selected locations close to the airfoil. Direct measurement of the flow Mach number is provided by schlieren visualizations. Experimental results agree with the shock wave theory for two-dimensional steady flows, complemented with state-of-the-art thermodynamic models, and deviate from their well-known, dilute-gas predictions. In particular, measurements show the non-ideal dependence of the pressure ratio across the shock on stagnation conditions in addition to the well-known dependence on the pre-shock Mach number, specific heat ratio and flow deviation angle typical of dilute gas conditions.Graphical abstract
Highlights
ObjectivesThe experimental investigation presented in this work aims at characterizing oblique shock waves in the non-ideal classical regime through independent measurements of pressure, temperature and Mach number, and to prove that, in this particular regime, the postshock state depends on both the total and local pre-shock conditions
The knowledge of the flow behavior in aerodynamic devices operating in dilute-gas conditions is well established and satisfactory
Active pressure taps are marked with a dot in a and b steady-state flow arrangement obtained at increasing value of the pre-shock, for which pre-shock, post-shock and post-expansion states can be determined following the procedure described in the previous paragraph
Summary
The experimental investigation presented in this work aims at characterizing oblique shock waves in the non-ideal classical regime through independent measurements of pressure, temperature and Mach number, and to prove that, in this particular regime, the postshock state depends on both the total and local pre-shock conditions
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