Laminar-turbulent transition in the boundary layer on cones in a hypersonic flow at high Reynolds numbers per meter

Abstract

The laminar-turbulent transition is experimentally studied in boundary-layer flows on cones with a rectangular axisymmetric step in the base part of the cone and without the step. The experiments are performed in an A-1 two-step piston-driven gas-dynamic facility with adiabatic compression of the working gas with Mach numbers at the nozzle exit M ∞ = 12-14 and pressures in the settling chamber P 0 = 60-600 MPa. These values of parameters allow obtaining Reynolds numbers per meter near the cone surface equal to Re 1e = (53-200) · 10 6 m −1 . The transition occurs at Reynolds numbers Re tr = (2.3-5.7) · 10 6 .Introduction. The separation properties of a hypersonic boundary layer passing from the laminar to the turbulent state at junctions of various elements of flying vehicles (in inlets, flaps, etc.) are often responsible for the flow pattern around the body as a whole and its aerodynamic characteristics.Boundary-layer stability and laminar-turbulent transition have been studied in many papers. Because of the restrictions on the paper volume, the state of the art of this problem cannot be discussed in detail (see [1][2][3][4][5][6][7]). Unlike [1-7], the data described below were obtained for stagnation parameters that have not yet been reproduced in a gas-dynamic experiment.The present paper describes the result of investigations of the laminar-turbulent transition in the boundary layer on cones with and without a rectangular step. The study was performed in an A-1 piston-driven twostep gas-dynamic facility with adiabatic compression [8]. Up to now, for free-stream Mach numbers M ∞ > 10, the range of natural (for promising hypersonic vehicles) free-stream Reynolds numbers could not be completely reproduced in experimental facilities (see, e.g., [9]), and the main source of data on the transition were in-flight results. A high pressure in the settling chamber of the A-1 facility (P 0 1000 MPa) and a rather low temperature (T 0 = 1200-2000 K) ensure obtaining record Reynolds numbers per meter (Re 1∞ = ρ ∞ v ∞ /μ ∞ ) at the nozzle exit.Even for comparatively small model sizes, this allows one to obtain, for M ∞ = 8-18, Reynolds numbers close to natural ones (for flight of promising hypersonic vehicles) and to observe (without artificial tripping) the boundarylayer transition from the laminar to the turbulent state at distances of the order of 30-50 mm from the tip of the model tested. The test time (20-200 msec) and the small size of the model allow one to assume the flow on all parts of the examined model to be steady and to obtain measurements at several points during one run.The A-1 layout and its operation principle were described in detail in [8]. The facility has the following limiting parameters: pressure in the settling chamber P 0 = 1000 MPa, maximum stagnation temperature T 0 =