Alexander Kuzmin

Sensitivity Analysis of Transonic Flow over J-78 Wings

3D transonic flow over swept and unswept wings with an J-78 airfoil at spanwise sections is studied numerically at negative and vanishing angles of attack. Solutions of the unsteady Reynolds-averaged Navier-Stokes equations are obtained with a finite-volume solver on unstructured meshes. The numerical simulation shows that adverse Mach numbers, at which the lift coefficient is highly sensitive to small perturbations, are larger than those obtained earlier for 2D flow. Due to the larger Mach numbers, there is an onset of self-exciting oscillations of shock waves on the wings. The swept wing exhibits a higher sensitivity to variations of the Mach number than the unswept one.

Structural Instability of Transonic Flow over an Airfoil

Inviscid transonic flow over the DSMA523a and Whitcomb airfoils and an airfoil described by a simple algebraic formula has been investigated numerically. The dependence of the flow structure and the lift coefficient on the freestream Mach number Minfin and the angle of attack α has been studied. The values of Minfin and α at which steady‐state flow becomes unstable have been revealed. The relationship between the flow nonuniqueness occurring in certain ranges of variation of Minfin and α and the instability has been analyzed.

Transonic flow past a Whitcomb airfoil with a deflected aileron

The sensitivity of transonic flow past a Whitcomb airfoil to deflections of an aileron is studied at free-stream Mach numbers from 0.81 to 0.86 and vanishing or negative angles of attack. Solutions of the Reynolds-averaged Navier-Stokes equations are obtained with a finite-volume solver using the k- ω SST turbulence model. The numerical study demonstrates the existence of narrow bands of the Mach number and aileron deflection angles that admit abrupt changes of the lift coefficient at small perturbations. In addition, computations reveal free-stream conditions in which the lift coefficient is independent of aileron deflections of up to 5 degrees. The anomalous behavior of the lift is explained by interplay of local supersonic regions on the airfoil. Both stationary and impulse changes of the aileron position are considered.

Adverse Free-Stream Conditions for Transonic Airfoils with Concave Arcs

Turbulent transonic flow past airfoils with concave arcs is studied using the RANS equations. The study is focused on adverse free-stream conditions, in which the lift coefficient exhibits abrupt changes under slight variations of the free-stream velocity or the angle of attack. For a Drela Apex 16 airfoil, the instability occurs at negative angles of attack α < 0. For a Whitcomb airfoil with a bump on the upper surface, the instability is obtained at 0 < α < 1 deg.

Instability of Shock Waves in Bent Channels of Rectangular Cross Section

The 2D and 3D turbulent airflow in channels with sharply bent walls is studied numerically. The inner surfaces of opposite walls are parallel to each other ahead of the bends and slightly divergent downstream. The inflow Mach number ranges from 1.2 to 1.5. Solutions of the Reynolds-averaged Navier-Stokes equations are obtained with a finite-volume solver on fine computational meshes. The solutions demonstrate flow hysteresis and bifurcations in considerable bands of the Mach number and angle of attack. The instability of shock waves is explained by their interaction with the expansion flow developed over the convex bend of a wall. Though the leading edges of walls are very thin, they produce noticeable effects on the flow.

Sensitivity analysis of transonic flow past a NASA airfoil / wing with spoiler deployments

Transonic flow past a NASA SC(2)-0710 airfoil with deployments of a spoiler up to 6° was studied numerically. We consider angles of attack from -0.6° to 0.6° and free-stream Mach numbers from 0.81 to 0.86. Solutions of the unsteady Reynoldsaveraged Navier-Stokes equations were obtained with a finite-volume solver using several turbulence models. Both stationary and time-dependent deployments of the spoiler were examined. The study revealed the existence of narrow bands of the Mach number, angle of attack, and spoiler deflection angle, in which the flow was extremely sensitive to small perturbations. Simulations of 3D flow past a swept wing confirmed the flow sensitivity to small perturbations of boundary conditions.

Instability of transonic flow past flattened airfoils

Transonic flow past a Whitcomb airfoil and two modifications of it at Reynolds numbers of the order of ten millions is studied. The numerical modeling is based on the system of Reynolds-averaged Navier-Stokes equations. The flow simulations show that variations of the lift coefficient versus the angle of attack become more abrupt with decreasing curvature of the airfoil in the midchord region. This is caused by an instability of closely spaced local supersonic regions on the upper surface of the airfoil.