Experimental technique for the investigation of artificially generated disturbances in planar laminar hypersonic boundary layers

A new experimental method to introduce artificially disturbances into flat plate boundary layers was studied in the Ludwieg-tube wind tunnel of the DLR in Göttingen at a free-stream Mach number of M₁ = 5. For the investigations, a 500 mm long and 20 mm thick flat plate model was used which spanned the test section 400 mm in width. As disturbance source a spark device flush mounted to the model surface close to its leading edge was utilized. The hot wire measurements of natural and forced disturbances in the boundary layer of the flat plate were conducted at different streamwise positions. The charge conditions of the wind tunnel used were almost constant at p_charge ≈ 5 bar and T_charge ≈ 393 K. This resulted in a unit Reynolds number of $\text{Re}{}_1\text{/l ≈ 6.74 1 10}{}^6\text{m}{}^{\mathrm{?1}}$ and a mass flow of ρ₁u₁ = 30.34 kg/m²s. To check the flow quality of the tunnel and the laminar characteristic of the boundary layer optically, Schlieren pictures were taken prior to each measurement campaign. The artificially inserted wave packets were successfully measured at different streamwise and spanwise locations downstream of the spark source. The main wave parameters, e.g. wave numbers and wave inclination angle were deduced from the measurements.