Using the oblique shock calculator is straightforward, but understanding the inputs and interpreting the results requires knowledge of compressible flow theory. Follow these steps to obtain accurate and meaningful results.
1. Determine the Upstream Mach Number
The upstream Mach number (M₁) is the most critical input. It must be greater than 1 for oblique shocks to form. This value can be obtained from flight data, wind tunnel measurements, or theoretical calculations. For aircraft applications, it's typically the flight Mach number. For wind tunnel tests, it's the test section Mach number. Ensure this value is accurate as it significantly affects all downstream properties.
2. Specify the Deflection Angle
The deflection angle (θ) represents how much the flow must turn to follow the surface geometry. For a wedge, this is simply the wedge angle. For more complex geometries, it's the effective turning angle. This angle must be within the valid range for the given Mach number - too large a deflection angle will result in a detached shock wave, which cannot be analyzed with the oblique shock theory.
3. Choose the Specific Heat Ratio
The specific heat ratio (γ) depends on the gas being analyzed. For air at standard conditions, γ = 1.4. For other gases, use appropriate values: γ = 1.67 for monatomic gases like helium, γ = 1.33 for diatomic gases at high temperatures, and γ = 1.3 for combustion products. This parameter affects how the flow properties change across the shock.
4. Interpret the Results
The calculator provides five key outputs: shock angle, pressure ratio, temperature ratio, density ratio, and downstream Mach number. The shock angle shows the orientation of the shock wave. The ratios indicate how much the flow properties increase across the shock. The downstream Mach number shows whether the flow remains supersonic or becomes subsonic after the shock.