Kazimierz Peszynski

Aerodynamic and mass transfer characteristics of an annular bistable impinging jet with a fluidic flip-flop control

Abstract An annular nozzle has been designed on the basis of fluidic principles. The nozzle forms actively controlled air jet. Numerical and experimental investigations were performed in several subsequent steps, namely numerical simulation (using a commercial CFD code FLUENT), geometry adaptation, models manufacturing, flow visualization, hot-wire measurement, and mass transfer (naphthalene sublimation) experiment. A “jet switching” possibility has been discussed, an undesirable hysteresis effect has been suppressed. Present collaborative numerical and experimental investigations have resulted in a better understanding of mechanisms involved in controlled impinging jets, as well as in a further improvement of the particular nozzle geometry.

Annular Impinging Jet Controlled by Radial Synthetic Jets

This experimental study focuses on generation and control of annular impinging jets. The annular nozzle used in the investigations was designed with an active flow control system using 12 synthetic jets issuing radially from the central nozzle body. Measurements of the control effects were made on the impingement wall. The data acquisition involved wall pressure and wall mass transfer (by the naphthalene sublimation technique) using air as the working fluid. Also measured was time-mean flow velocity (by a Pitot probe) in the jet flow field. Moreover, flow visualization was carried out. Two main flow-field patterns (A and B) were identified. The patterns differ in the size of the separated-flow recirculation regions that develop attached to the nozzle central body: While pattern A is characterized by a quite small recirculation region (bubble) extending not far from the nozzle exit, pattern B exhibits a large recirculation region, reaching up to the impingement wall, on which it forms a stagnation circle. The control action modifies the flow field, resulting in changes of the corresponding heat/mass transfer distributions. The convective transfer rate on the stagnation circle can be demonstrably enhanced by 20% at a moderate nozzle-to-wall distance, equal to 0.6 of the nozzle outer diameter.

Modelling of air flow rate in significantly flattened rounded rectangular ventilation ducts

Paper presents new mathematical model for air flow velocity distribution in rounded rectangular ducts and its experimental verification. In papers [1, 2] an mathematical model based on modified Prandtl equation for power power-law velocity profile was determined. It works very well for smaller cross sections. During the study of larger cross sections new phenomena in flowing air have been observed, it forced the search for a new model. The new model is based on a rounded rectangular division into two parts: slot and rounded square.