According to a model of the turbulent boundary layer proposed by the authors,
in the absence of external turbulence the intermediate region between the
viscous sublayer and the external flow consists of two sharply separated
self-similar structures. The velocity distribution in these structures is
described by two different scaling laws. The mean velocity u in the region
adjacent to the viscous sublayer is described by the previously obtained
Reynolds-number-dependent scaling law ϕ=u/u∗=Aηα,
A=31lnReΛ+25, α=2lnReΛ3,
η=u∗y/ν. (Here u∗ is the dynamic or friction velocity, y is the
distance from the wall, ν the kinematic viscosity of the fluid, and the
Reynolds number ReΛ is well defined by the data) In the region
adjacent to the external flow the scaling law is different: ϕ=Bηβ. The power β for zero-pressure-gradient boundary layers
was found by processing various experimental data and is close (with some
scatter) to 0.2. We show here that for non-zero-pressure-gradient boundary
layers, the power β is larger than 0.2 in the case of adverse pressure
gradient and less than 0.2 for favourable pressure gradient. Similarity
analysis suggests that both the coefficient B and the power β depend on
ReΛ and on a new dimensionless parameter P proportional to the
pressure gradient. Recent experimental data of Perry, Maru\v{s}i\'c and Jones
(1)-(4) were analyzed and the results are in agreement with the model we
propose.Comment: 10 pages, 9 figure