In the mixing of a jet with a cross-stream, it is found that in the near field, defined as the region of the flow from the jet exit to a distance of a few diameters downstream of this exit, a considerable amount of dynamical adjustment takes place. This near-field region characterizes the subsequent behaviour and development of the jet, its wake and the cross-stream in the vicinity of this mixing region. The rapid evolution of the flow gives rise to a pair of bound vortices attached to the lee side of the jet boundary, to fast development of the turbulent and mean vorticity, to a vortex-shedding system, and to the largest rates of entrainment of cross-stream flow into the jet. Furthermore, it is found that the geometrical configuration of the boundaries at the jet exit plays an important role in the mixing and development processes.An intrinsic method is proposed for the delineation of the flow boundaries between the jet and the cross-stream. Calculations of mass, momentum and vorticity fluxes have been made. The vorticity flux gives evidence of the rapid stretching and tilting of the vorticity vector field in the near-field region.

Three-dimensional flowfields in a centrifugal impeller with backswept discharge at various operating points have been numerically investigated with a three-dimensional viscous flow code. Numerical results and experimental data were compared for the detailed flowfields and overall performance of the impeller at three operating conditions (optimum efficiency, choke, and near-surge conditions). The comparisons indicate that for engineering applications the numerical solution accurately predicts various complex real flow phenomena. The overall aerodynamic performance of the impeller is also well predicted at design and off-design conditions.

Centrifugal compressor stages with pipe diffusers are considered to perform with high efficiency. Yet very little information on these kinds of diffusers is available to this day. Therefore, experimental investigations have been performed on a centrifugal compressor stage with a pipe diffuser. An extensive measurement series using various steady, unsteady and laser optical measurement techniques has been performed to detect the highly three dimensional diffuser flow and create a benchmark for further development steps. Whereas this paper presents the test rig and the results gathered under nominal conditions, in a follow-up paper the results of the parameter variation studies covering bleed variation, impeller tip clearance and impeller-diffuser misalignment are compared to the nominal baseline and evaluated with respect to the compressor stage performance. For the investigations performed under nominal conditions it was found that the diffuser flow separates on the pressure side in the first half of the pipe. In the last 30% of the pipe hardly any deceleration of the flow takes place. From this, special attention is drawn to the parameter variations regarding a first proposal for a diffuser design change, which consists in shortening the diffuser. Ongoing investigations cover this design proposal. Along with the results of the ongoing investigations, the numerical investigations accompanying the experimental work will also be presented in follow-up papers.

The use of a single inclined hot wire for measurments of mean flow velocity and direction in a three−dimensional turbulent flow field is presented. A constant temperature hot−wire anemometer circuit is used with and without a linearizer. The use of the linearized results were found to improve the readout ability of the instrument and also to simplify the correction for directional measurements. A study of the effect of turbulence levels on the steady calibration results has shown that if the turbulence levels and the cross correlations are known, corrections can be applied to obtain angles and velocities as reliable as those obtained from a directional pressure probe. The advantages of the use of the hot wire over a pressure probe are that the hot wire has much faster response, disturbs the flow field to a lesser degree, is easier to correct for turbulence levels, and due to its smaller dimension compared with the pressure probe is less erratic concerning mean velocity gradients. The method of measurement and correction was tested in a jet mixing with a cross wind field. The range of angles shown in the experimental graphs pertain to that of a jet mixing with a cross wind.