Khalatov A.A., Institute of Engineering Thermophysics, National Academy of Sciences of Ukraine

The fundamental aspects of vortex technologies and their applications to aerospace engineering have been studied in the Ukraine for many years. The Institute of Engineering Thermophysics being at the forefront of many advanced aerospace programs has contributed many novel results both into the science and technology. Following from these programs, a few international projects funded by the Royal Society (UK), NATO Scientific Committee (Belgium), Civilian Research and Development Foundation (USA) and other international agencies have been carried out in the Ukraine over the last six years. This presentation outlines the primary results, as well as the most important data obtained in other countries.

Introduction. Examples are given of induced vortices applied in engineering and technology. They include the Karman ‘vortex street’ in cross flow and behind periodic ribs; trailing vortices; vortices generated by half-delta wings and above; array of rectangular winglets; Görtler and Dean vortices in curvilinear systems; in-passage swirl flow; vortices over an end wall gas turbine’s guide vane.

Blade Cyclone Cooling. The thermal potential of conventional blade internal cooling techniques (impingement cooling; surface ribbing; pin-fins; flow oscillations) is virtually exhausted. The further rise in the gas turbine entry temperature can be achieved either through increase in the coolant flow rate, or via reductions in a cooling passage size leading to a dirt blockage problem. Some advanced cooling concepts are now under consideration throughout the world, among those the cyclone (screw) cooling concept plays one of the leading role.

The cyclone cooling is based on generation of swirl flow in blade cooling passage. As found, the high ratio of heat transfer of up to a factor 7.0 as compared with axial counterpart can be achieved in a blade cooling passage at acceptable mass per unit area flow rate. The flexibility to external boundary conditions, easy ability to adjust internal and external heat transfer, less sensitivity to fabrication tolerances, and finally relatively simple and cost effective technology allowing to avoid manufacture of very small size features (passages; ribs) make this technology especially attractive in design of advanced blade cooling systems. The presentation reviews the currently available cyclone cooling designs, such as two- and three dimensional configurations, three passage serpentine configuration, vortex chamber with tangential and inclined impingement cooling. The results of experimental testing and numerical simulation are presented, a comparison with traditional cooling techniques and conventional designs is given along with the thermal-hydraulic performance evaluation.

Surface Dimple Technique. This vortex technique is based on formation of the ‘self-organized’ oscillating vortex structures, bursting periodically into a downstream flow. The small scale vortex has the unique ‘tornado-like’ structure, promoting the rotational momentum concentration in the vortex axis area. The non-conventional dissipation mechanism via the series of ‘ring vortices’ absorption in a main flow contributes an approximately equivalent growth of heat transfer and pressure losses, which is very unusual feature in turbulent flow conditions. The heat transfer enhancement rate factor of 2.5 - 2.7 has been achieved in experimental studies over a flat dimpled plate at the pressure drop factor of 2.8 - 4.2 giving the extra-ordinary thermal-hydraulic performance.
Results of experimental and theoretical studies have been analyzed and summarized. This includes a single dimple, array of dimples and associated flow patterns; effects of surface curvature, pressure gradient, free-stream turbulence and channel height. Some novel results regarding combustion process, oscillating film cooling, flow separation control on the aeroengine low pressure turbine blade, cooling of combustor lines are also considered. Comparison with other heat transfer techniques in terms of the thermal-hydraulic performance is given to illustrate the non-trivial features of this technique.

Vortex Matrix. The idea of vortex matrix is based on generation of the multiple-crossed swirl flow in each rectangular-shaped passage of the vortex matrix. The high rate of heat transfer enhancement (Nu/Nu0 = 2.2 - 2.9), approximately uniform heat transfer level throughout the matrix surface, acceptable thermal-hydraulic performance, high integrity and longer operating life make this concept especially attractive in design of internal cooling systems. The presentation summarizes the available database, obtained mainly in the former USSR and includes results of heat transfer and aerodynamics studies and analysis of existing blade designs.

Guide Vane End Wall. A horseshoe vortex, a passage vortex and cluster of corner vortices form the vortex structures existing over a guide vane end wall. Broad investigations of the end wall vortex structures have been undertaken over the last twenty years towards understanding the flow physics, heat transfer and film cooling mechanism, obtaining the reference heat transfer and fluid flow correlations. The presentation reviews recent results obtained in the Institute of Engineering Thermophysics in collaboration with the Air Force Institute (Ukraine). The vast database covers new approach at a heat transfer analysis, based on the multiplication theory, results of convective heat transfer and film cooling studies, effects of the aspect ratio, boundary layer thickness and turbulence, coolant injection through a permeable end wall, a passage vortex interaction with a blade suction side. The range of correction functions highlighting the ‘isolated’ effects of a secondary flow, transverse and streamwise pressure gradient, free-stream turbulence, porous injection useful in practice is presented. Some recent results dealing with the complex angle end wall film cooling and contoured end wall are also considered.

Conclusions. The potential of vortex technologies in aerospace engineering is discussed. Examples of the most successful applications of vortex technologies in other than aerospace engineering field are also given.