Developing Turbulent Boundary Layers Research Articles

A Waveguide Model of the Developed Turbulent Boundary Layer

A Waveguide Model of the Developed Turbulent Boundary Layer

A Waveguide Model of the Developed Turbulent Boundary Layer

A study of the developed turbulent boundary layer that emerges when incompressible viscous fluid flows around a plate at a zero angle of attack and with zero longitudinal pressure gradient is presented. The waveguide approach is used for describing the turbulent boundary layer; in this approach, turbulent fluctuations are related with Tollmien–Schlichting waves that are in three-wave resonance. To study the original nonlinear system of equations, an estimate of hydrodynamic quantities is proposed that does not violate the generally accepted approach in the boundary layer but leads to the appearance of a new small parameter—the ratio of the thickness of the boundary layer momentum loss to the damping length of the least damped mode of the Tollmien–Schlichting waves. Equations for the coherent and stochastic parts of fluctuations are obtained on the basis of the method of multiple scales. The dispersion characteristics of waves of the least damped mode on the profile of the average longitudinal velocity of the developed turbulent boundary layer are determined, and the conditions for the multiple three-wave resonance of this mode of the Tollmien–Schlichting waves are analyzed. For the coherent part of the fluctuations, the fluctuation characteristics are compared with the known numerical results.

Statistics of Particle Accumulation in Spatially Developing Turbulent Boundary Layers

We present the results of a Direct Numerical Simulation of a particle-laden spatially developing turbulent boundary layer up to Re θ = 2500. Two main features differentiate the behavior of inertial particles in a zero-pressure-gradient turbulent boundary layer from the more commonly studied case of a parallel channel flow. The first is the variation along the streamwise direction of the local dimensionless parameters defining the fluid-particle interactions. The second is the coexistence of an irrotational free-stream and a near-wall rotational turbulent flow. As concerns the first issue, an inner and an outer Stokes number can be defined using inner and outer flow units. The inner Stokes number governs the near-wall behavior similarly to the case of channel flow. To understand the effect of a laminar-turbulent interface, we examine the behavior of particles initially released in the free stream and show that they present a distinct behavior with respect to those directly injected inside the boundary layer. A region of minimum concentration occurs inside the turbulent boundary layer at about one displacement thickness from the wall. Its formation is due to the competition between two transport mechanisms: a relatively slow turbulent diffusion towards the buffer layer and a fast turbophoretic drift towards the wall.

Modeling the freestream parameter effect on unsteady boundary layers with positive pressure gradients

The dynamic and thermal parameters of steady and unsteady wall boundary layers are studied on the basis of a two-equation turbulence model under high freestream turbulence intensity and the action of a longitudinal pressure gradient. The freestream parameter effect on the development of dynamic and thermal processes in a steady developed turbulent boundary layer in the flow deceleration zone with a positive pressure gradient is investigated using the modified K-ɛ model. The boundary layer structure is studied and the calculated profiles of the velocity and the kinetic energy of turbulence are compared with the experimental data for the preseparation region. The possibility of the theoretical description of developed turbulent regimes by a quasi-steady turbulence model in the case of periodic temporal dependence of the freestream velocity is shown. An analysis of the calculated parameters of the dynamic and thermal unsteady turbulent boundary layers makes it possible to determine their properties at different oscillation parameters for regions with both zero and positive pressure gradients. The numerical results are compared with experimental data.

Response of Taut Strip Models to Turbulent Wind

An experimental investigation was conducted to clarify the fundamental behaviour of the proposed taut strip wind tunnel model of long span bridge deck systems. The study shows that this method is relatively simple and convenient and yet effective method of investigating the aerodynamic behaviour of long span bridges with the simulation of natural wind turbulence in laboratory scale. Experimental results are compared with the simple theoretical calculation and some aerodynamic characteristics of bridge response in highly developed turbulent boundary layer flow were observed. Effect of scale of turbulence in particular is found to be significant.

Closure to “Discussion of ‘The Response of a Developed Turbulent Boundary Layer to Local Transverse Surface Motion’” (1976, ASME J. Fluids Eng., 98, p. 363)

Closure to “Discussion of ‘The Response of a Developed Turbulent Boundary Layer to Local Transverse Surface Motion’” (1976, ASME J. Fluids Eng., 98, p. 363)

The Response of a Developed Turbulent Boundary Layer to Local Transverse Surface Motion

Measurements were obtained of the mean velocity, Reynolds stress tensor components and spectral distribution of turbulent energy in a boundary layer that was adjusting spatially from a collateral to a three-dimensional state because of transverse motion of the bounding wall. The results indicate that changes to the turbulent structure lead to a strong coupling between the axial and transverse components of mean velocity. The influence of the imposed motion was found to be confined to a discrete region near the wall over the first ten initial boundary layer thicknesses, after which it became more global in nature.