Diamantis Kounadis

Experimental Study of the Flow and Thermal Development of a Row of Cooling Jets Impinging on a Rotating Concave Surface

The paper reports an experimental study of impingement cooling in a rotating passage of semi-cylindrical cross section. Cooling fluid is injected from a row of five jet holes along the centerline of the flat surface of the passage and strikes the concave surface. The cooling passage rotates orthogonally about an axis parallel to that of the jets. Tests have been carried out, using water both within the passage and as the jet fluid, at a fixed Reynolds number of 15,000, for clockwise and counter-clockwise rotation. Local Nusselt number measurements, using the liquid-crystal technique, show that under stationary conditions a high Nusselt number region develops around each impingement point, with secondary peaks half-way between impingement points. Rotation reduces heat transfer, leads to the disappearance of all secondary peaks and also, surprisingly of some of the primary peaks. Flow visualization tests suggest that these changes in thermal behavior are caused because rotation increases the spreading rate of the jets. LDA and PIV measurements are also presented. They show that under stationary conditions the five jets exhibit a similar behavior, with their cores remaining intact up to the point of impingement at the top dead center. The LDA and PIV studies help explain the rather surprising thermal behavior under rotating conditions.

Head-on collision of shock wave induced vortices with solid and perforated walls

An experimental study has been conducted to examine the interaction of shock wave induced vortices with a flat plate and a perforated plate. The experiments were carried out using a 30mm internal diameter shock-tube at Mach numbers 1.31, 1.49, and 1.61 under critical driver conditions. Air was used both in the driver and driven sections. High-speed schlieren photography was employed to study the flow development and the resulting interactions with the plates. Wall pressure measurements on both plates were also carried out in order to study the flow interactions quantitatively. The experimental results indicated that a region of strong flow development is generated near the wall surface, due to the flow interactions of reflected waves and oncoming induced vortices. This flow behavior causes the generation of multiple pressure fluctuations on the wall. In the case of the perforated plate, a weaker initial reflected wave is produced, which is followed by compression waves, due to the internal reflections wit...

Vortex Ring Interaction Studies with a Cylinder and a Sphere

*† ‡ § ** An experimental study has been conducted to examine the interaction of a shock wave and a vortex ring with a cylinder and a sphere. The experiments were carried out using a 30mm internal diameter shock-tube. The driver and driven gas was air. High-speed Schlieren photography was employed to study the development of the flow-field and the resulting interactions with the body configurations. Wall pressure measurements were also carried out to study the flow quantitatively at the apex of the cylindrical surface. Three different driver pressures of 4, 8, and 12 bar were examined under maximum driver length (1477mm); the shock wave Mach number at the exit of the tube was 1.33, 1.52 and 1.67 respectively. Nomenclature a1 = speed of sound (m/s) in region one a2 = speed of sound (m/s) in region two a3 = speed of sound (m/s) in region there a4 = speed of sound (m/s) in region four M1 = incident Mach number M3 = Mach number in region three P1 = static pressure (bar) in region one P2 = static pressure (bar) in region two P3 = static pressure (bar) in region three P4 = static pressure (bar) in region four R = universal gas constant (J/kgK) t = time (ms) count from the rupture of the diaphragm t3 = time (ms) of the reflected rarefaction head meets the rarefaction tail tc = time (ms) when rarefaction head overtakes the contact surface

Head-on Interaction of Shock Waves and Vortex Rings with Solid and Perforated Walls

An experimental study has been conducted to examine the interaction of a shock wave and a vortex ring with a at plate and a perforated plate. The experiments were carried out using a 30mm internal diameter shock-tube. The driver and driven gas was air. Highspeed Schlieren photography was employed to study the development of the o w-eld and the resulting interactions with the plates. Wall pressure measurements were also carried out to study the o w quantitatively at the exit of the shock-tube. Three dieren t driver pressures of 4, 8 and 12bar were examined under critical driver length conditions; the shock wave Mach number was 1.33, 1.52 and 1.67, respectively.

Application of pressure-sensitive paints in high-speed flows

Pressure-sensitive paint (PSP) has become a useful tool to augment conventional pressure taps in measuring the surface pressure distribution of aerodynamic components (Mosharov et al. [1]). PSP offers the advantage of nonintrusive global mapping of the surface pressure.

Shock wave interactions inside a complex geometry

Studies of shocks expanding into confined regions lack detailed quantitative data of major flowfield features that evolve in time. The transient behaviour of shock waves and detonations has been the subject of study of many investigators. These include phenomena such as shock reflections, diffractions and shock/vortex interactions. The mentioned phenomena have been explored by various authors, for example shock wave reflections have been studied both phenomenon experimentally and analytically by Ben-Dor and Takayama [1], Ben-Dor et al. [2] and Henderson and Lozzi [3]. The shock diffraction pattern over corners at different Mach numbers has been studied experimentally by Skews ([4], [5]) and also by Griffith and Bricklet [6]. Shock diffraction from small areas to larger ones, have been studied by authors such as, Jiang et al. [7] and Chang and Kim [8].

Experimental Study of the Thermal Development in a Rotating Square-Ended U-Bend

This paper reports an experimental study of the thermal development in an idealized model of a blade cooling passage of smooth inner surfaces, comprising a square-ended U-bend with a cross-section that changes from a square upstream to a 2:1 rectangle downstream of the turn. The two flat walls are heated electrically, while the outer wall and the splitter plate are thermally insulated. The steady state liquid crystal technique is used to map the local Nusselt number variation. Measurements are obtained using a stationary air flow facility and also a rotating water flow facility. This enables us to investigate the effects on the thermal development of Reynolds variation from 30,000 to 100,000, Prandtl numbers of 0.7 and 5.8, and rotation numbers, from 0 to 0.4. The effects of minor modifications in the cross-sectional area at the bend exit, on the thermal development, under both stationary and rotating conditions, are also explored.Copyright

Development of Flowfield and Surface Heat-transfer Measurement and Visualisation Techniques for Internal Rotating Cooling Flows in Gas Turbine Blades

This paper reviews the authors experimental investigations of heat and fluid flow through rotating cooling passages, relevant to the internal cooling of gas turbine blades. The main experimental facility used is a rotating water flow table. While sacri