Flying-Hot-wire Study of Flow Past an NACA 4412 Airfoil at Maximum Lift

Coles, Donald; Wadcock, Alan J.

doi:10.2514/3.61127

Cited by 218 publications

(81 citation statements)

References 3 publications

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“…Substitution of a linear ramp signal for the oscillating surface pressure reduced the assignment of phase to a simple calculation using binary t In an experiment involving measurements with the same flying-hot-wire apparatus in the wake of a stalled airfoil, a different and unexpected kind of rotor interference was encountered. This problem is described and discussed by Coles & Wadcock (1979).…”

Section: Data Processingmentioning

confidence: 99%

An experimental study of entrainment and transport in the turbulent near wake of a circular cylinder

1983

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This paper describes an experimental investigation of transport processes in the near wake of a circular cylinder a t a Reynolds number of 140000. The flow in the first eight diameters of the wake was measured using X-array hot-wire probes mounted on a pair of whirling arms. This flying-hot-wire technique increases the relative velocity component along the probe axis and thus decreases the relative flow angle to usable values in regions where fluctuations in flow velocity and direction are large. One valuable fringe benefit of the technique is that rotation of the arms in a uniform flow applies a wide range of relative flow angles to the X-arrays, making them inherently self-calibrating in pitch. An analog circuit was used to generate an intermittency signal, and a fast surface-pressure sensor was used to generate a phase signal synchronized with the vortex-shedding process. The phase signal allowed sorting of the velocity data into 16 populations, each having essentially constant phase. An ensemble average for each population yielded a sequence of pictures of the instantaneous mean flow field, with the vortices frozen as they would be in a photograph. I n addition to globally averaged data for velocity and stress, the measurements yield non-steady mean data (in the sense of an average a t constant phase) for velocity, intermittency, vorticity, stress and turbulent-energy production as a function of phase for the first eight diameters of the near wake. The stresses were resolved into a contribution from the periodic motion and a contribution from the random motion at constant phase. The two contributions are found to have comparable amplitudes but quite different geometries, and the time average of their sum (the conventional global Reynolds stress) therefore has a quite-complex structure. The non-steady mean-vorticity field is obtained with good resolution as the curl of the non-steady mean-velocity field. Less than half of the shed circulation appears in the vortices, and there is a slow decay of this circulation for each shed vortex as it moves downstream. In the discussion, considerable emphasis is put on the topology of the non-steady mean flow, which emerges as a pattern of centres and saddles in a frame of reference moving with the eddies. The kinematics of the vortex-formation process are described in terms of the formation and evolution of saddle points between vortices in the first few diameters of the near wake. One important conclusion is that a substantial part of the turbulence production is concentrated near the saddles and that the mechanism of turbulence production is probably vortex stretching a t 322 intermediate scales. Entrainment is also found to be closely associated with saddles and to be concentrated near the upstream-facing interface of each vortex.

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Section: Data Processingmentioning

confidence: 99%

An experimental study of entrainment and transport in the turbulent near wake of a circular cylinder

1983

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“…The time-advancement algorithm is based on the linearized backward Euler time-differencing scheme, which yields a linear system of equations for the solution at each time step: (15) where is the vector of steady-state residuals, represents the change in the dependent variables, and (16) The solution of this system of equations is obtained with either a fully vectorizable point implicit Gauss-Seidel procedure 1,3 or a preconditioned GMRES procedure. 37 When using the Gauss-Seidel procedure, the solution of the linear system is obtained by a relaxation scheme in which is obtained through a sequence of iterates that converge to .…”

Section: Time-advancement Schemementioning

confidence: 99%

“…37 When using the Gauss-Seidel procedure, the solution of the linear system is obtained by a relaxation scheme in which is obtained through a sequence of iterates that converge to . To clarify the scheme, is first written as a linear combination of two matrices that represent the diagonal and off-diagonal terms: (17) The simplest iterative scheme for obtaining a solution to the linear system of equations is a Jacobi type of method in which all off-diagonal terms (i.e., ) are taken to the right-hand side of equation (15) and are evaluated with the values of from the previous subiteration level . This scheme can be represented as (18) The convergence rate of this process can be slow but can be accelerated somewhat by using the latest values of as soon as they are available.…”

Section: Time-advancement Schemementioning

confidence: 99%

Implicit/Multigrid Algorithms for Incompressible Turbulent Flows on Unstructured Grids

Anderson

Rausch²,

Bonhaus

1996

Journal of Computational Physics

202

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SummaryAn implicit code for computing inviscid and viscous incompressible flows on unstructured grids is described. The foundation of the code is a backward Euler time discretization for which the linear system is approximately solved at each time step with either a point implicit method or a preconditioned Generalized Minimal Residual (GMRES) technique. For the GMRES calculations, several techniques are investigated for forming the matrix-vector product. Convergence acceleration is achieved through a multigrid scheme that uses non-nested coarse grids that are generated using a technique described in the present paper. Convergence characteristics are investigated and results are compared with an exact solution for the inviscid flow over a four-element airfoil. Viscous results, which are compared with experimental data, include the turbulent flow over a NACA 4412 airfoil, a three-element airfoil for which Mach number effects are investigated, and three-dimensional flow over a wing with a partial-span flap.

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“…The flying hot wire was later used to study 2-D separation 13 and 2-D mean flow 14 on an NACA 4412 airfoil (e.g. Wadcock 13 and Coles and Wadcock 14 ). Their configuration consisted of a streamlined strut extending into the tunnel.…”

Section: B Previous Workmentioning

confidence: 99%

Separation-Bubble Velocity Measurements Using an Oscillating-Hot-Wire System.

Saric¹

1991

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A system is developed to allow measurement of both the mean and disturbance flow velocities in separated regions. An oscillating-arm assembly provides a directional bias to the hot-wire probe, along with a linear-step assembly, which steps the probe through the boundary layer. This system is used to investigate the flow field associated with laminar separation bubbles. A series of velocity profiles are measured on an FX63-137 airfoil in the chord-Reynolds-number range: 150,000 < R, < 300,000, at angles of attack of a = 120 and a = 14'. Data are presented on the size of the separation bubble and on the location of transition to turbulence. Interests in the use of low-Reynolds-number airfoils has established demands for better qualitative and quantitative understanding of the flow associated with these airfoils. In particular, detailed boundary-layer information is needed to aid in both physical understanding and theoretical development. At the lower range of chord Reynolds numbers, Rc, down to Rc = 10,000, the airfoil performance (measured by lift-to-drag ratio) rapidly deteriorates, as shown by Miley 1 . The drop in performance is due to increased skin friction (thus an increase in the drag) and the fact that the airfoil can behave like a flat plate. To account for the increase in drag, airfoils have been designed with strong adverse pressure gradients to increase lift. These strong adverse pressure gradients, however, stimulate laminar boundary layer separation and violent stall. A thorough review of all aspects of work in this area is given by Mueller 2 .Associated with laminar separation is the formation of a free shear layer. Under most conditions, the inherently unstable character of the free shear layer results in transition to turbulence. In the case where the turbulent shear layer reattaches as a turbulent boundary layer, a separation bubble is formed. With the presence of a separation bubble, lift is maintained and the characteristics of stall are avoided. On the other hand, if velocity disturbance amplitudes are sufficiently high, transition will occur first and separation will be avoided.Because of the low Reynolds numbers associated with these airfoils, separation is in a laminar boundary layer or a transitional boundary layer. Individually, separation and transition are phenomena that are very sensitive to environmental conditions such as free-stream turbulence, roughness, and noise. Therefore it is important to study the behavior of these airfoils in low-disturbance environments characteristic of flight. This is clearly a stability problem involving adverse pressure gradients. Although the problem is not new, most earlier work has dealt with a two-dimensional back step geometry (Lochtenberg 3 , Browand 4 , Roshko 5 , Goldstein, Ericksen, Olsen and Eckert 6 ) or the exit of axisymmetric free jets (Freymuth 7 , Moore', Davies and Baxter'). More recently, LeBlanc, Blackwelder, and Liebeck 10 have studied the free shear layer resulting from separation over a low Reynolds number airfoil.In orde...

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Flying-Hot-wire Study of Flow Past an NACA 4412 Airfoil at Maximum Lift

Cited by 218 publications

References 3 publications

An experimental study of entrainment and transport in the turbulent near wake of a circular cylinder

An experimental study of entrainment and transport in the turbulent near wake of a circular cylinder

Implicit/Multigrid Algorithms for Incompressible Turbulent Flows on Unstructured Grids

Separation-Bubble Velocity Measurements Using an Oscillating-Hot-Wire System.

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