This survey covers recent developments and applications of four skin-friction measurement techniques (oil-film interferometry, wall hot wire, surface fence and wall pulsed wire). Comparisons of the techniques with each other and with other methods are presented. Applications in attached and separated fully turbulent boundary layers and in highly accelerated laminar-like flows will be shown to demonstrate the application range and the limits of the various techniques.
This is an experimental investigation of two turbulent boundary
layers (cases 2 and
4) where the streamwise negative pressure gradient changes mean properties
of the
flow, e.g. mean velocity profiles and skin friction, so that they display
laminar-like
behaviour. The maximum acceleration parameter K[les ]4×10−6
and the starting value of the Reynolds number is 862 or 2564. Relaminarization
occurs
in both boundary layers as a gradual change of the turbulence properties
and is not
catastrophic. Retransition, however, is a fast process due to the remaining
turbulence
structure and may be compared with bypass transition. Together with an
extensive investigation
of the turbulence structure as in the companion paper, Part 1, which describes
two cases
(1 and 3) of boundary layers which remain turbulent, spectra and integral
length
scales for all four boundary layers are discussed.
The effects of a favourable pressure gradient
(K[les ]4×10−6) and of the Reynolds number
(862[les ]Reδ2[les ]5800) on the mean
and fluctuating quantities of four turbulent
boundary layers were studied experimentally and are presented in this paper
and a
companion paper (Part 2). The measurements consist of extensive hot-wire
and skin-friction
data. The former comprise mean and fluctuating velocities, their correlations
and spectra, the latter wall-shear stress measurements obtained by four
different
techniques which allow testing of calibrations in both laminar-like and
turbulent
flows for the first time. The measurements provide complete data sets,
obtained in
an axisymmetric test section, which can serve as test cases as specified
by the 1981
Stanford conference.Two different types of accelerated boundary layers were investigated
and are
described: in this paper (Part 1) the fully turbulent, accelerated boundary
layer
(sometimes denoted laminarescent) with approximately local equilibrium
between
the production and dissipation of the turbulent energy and with relaxation
to a zero
pressure gradient flow (cases 1 and 3); and in Part 2 the strongly accelerated
boundary
layer with ‘inactive’ turbulence, laminar-like mean flow behaviour
(relaminarized),
and reversion to the turbulent state (cases 2 and 4). In all four cases
the standard
logarithmic law fails but there is no single parametric criterion which
denotes the
beginning or the end of this breakdown. However, it can be demonstrated
that the
departure of the mean-velocity profile is accompanied by characteristic
changes of
turbulent quantities, such as the maxima of the Reynolds stresses or the
fluctuating
value of the skin friction.The boundary layers described here are maintained in the laminarescent
state just
up to the beginning of relaminarization and then relaxed to the turbulent
state in a
zero pressure gradient. The relaxation of the turbulence structure occurs
much faster
than in an adverse pressure gradient. In the accelerating boundary layer
absolute
values of the Reynolds stresses remain more or less constant in the outer
region of
the boundary layer in accordance with the results of Blackwelder &
Kovasznay (1972),
and rise both in the vincinity of the wall in conjunction with the rising
wall shear
stress and in the centre region of the boundary layer with the increase
of production.
In its Gas Turbine Development and Manufacturing Center in Berlin Siemens runs a test bed for gas turbine prototypes. Since the end of 1998, the new model V84.3A gas turbine has been undergoing tests at this facility. One focus of last year’s tests was on flow field measurements with pneumatic probes in the exit flow duct of the turbine at various load levels to characterize the flow in the diffuser and provide a data base. Another item was the further investigation of the compressor surge margin and the validation of a newly-developed on-line surge prediction system.
In order to get information on how pressure fluctuations in the combustion chamber of a gas turbine act on the gas piping system and adapters for measurement of pressure fluctuations, a one-dimensional, compressible, unsteady, anisentropic code is applied. This is done to obtain more detailed information about particular flow phenomena like wave propagation, superposition and the influence of heat transfer and damping. The model used was formed by using the one-dimensional equation laws of mass, momentum and energy to a hyperbolic differential equation system. This system was solved numerically by using the well proven PROMO code originating from the automotive industry as described in detail by Go¨rg [1]. The existing model was extended and adapted to be applicable to the problems described above.
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