Takaaki Shizawa

Optimal injection condition of a single pulsed vortex generator jet to promote the cross-stream mixing

Abstract The flow field of a pulsed vortex generator jet which is injected periodically through a single hole into a boundary layer is described. Measurements of phase-averaged velocity and wall shear stress are made by a hot-wire anemometer and a high response micro-wall flow sensor, respectively. Optimal mixing conditions, based on three parameters, (i) velocity ratio, (ii) duty ratio and (iii) pulse injection frequency, are discussed. The longitudinal vortex structure characteristic of steady injection is obtained at the stable stage of the evolution of the pulsed jet. A peak of the wall shear stress is also observed at the final stage. These mechanisms in the pulsed vortex generator jet enhance the cross-stream mixing to inhibit the boundary layer separation.

Behaviors of the Laterally Injected Jet in Film Cooling: Measurements of Surface Temperature and Velocity/Temperature Field Within the Jet

This paper presents the behaviors of the injected jet on the flat surface in lateral injection of the film-cooling. Simultaneous velocity and temperature measurements were made by the double-wire probe. The test surface was also covered with an encapsulated temperature-sensitive liquid crystal. The image processing system based on the temperature and hue of the liquid crystal calibration provides the surface temperature distributions. The tests were conducted at three kinds of mass flux ratio of 0.5, 0.85, and 1.2. The laterally injected jet has an asymmetric structure with a large scale of vortex motion in one side caused by the interaction with the primary stream. Asymmetry is promoted with mass flux ratio increased, resulting in low film-cooling effectiveness.Copyright

Experimental study of horseshoe vortex at wing/body junction with attack angle by triple hot-wire

This paper presents an experimental study focused on the structure of a horseshoe vortex at a wing/body junction. A flat wing is established on the flat wall where the two-dimensional turbulent boundary layer is fully developed. An attack angle of the wing is changeable from +15 to -15 deg every 5 deg. The reference velocity is 16.2 m/s; the boundary layer thickness at the leading edge of the wing is about 22 mm, and the Reynolds number based on the radius of curvature is 24,000. Total pressure was measured by a three-hole Pitot probe, and turbulence intensity was measured by a normal hot-wire anemometer. Three components of mean velocity and six components of Reynolds stress were measured simultaneously by a specially designed triple hot-wire. The pressure loss at the downwash side of the vortex is small, but it takes a large value at the upwash side. The loss is large at the suction side of the wing. The vortex center shifts from the wing in the downstream direction at the suction side. The location where the Reynolds stress takes a negative value does not correspond to the region of the negative mean velocity gradient at the upstream location. (Author)

Flow Behavior With an Oscillating Motion of the Impinging Jet in a Dump Diffuser Combustor

This paper presents flow behavior with an oscillating motion of an impinging jet upon a flame dome head and its reattachment to the casing wall, when a distorted flow is provided at the inlet of the dump diffuser combustor. A Laser-Doppler Velocimeter was used for the measurements of the time-averaged flow within a sudden expansion region. A surface pressure fluctuation survey on the flame dome head and flow visualization by a smoke wire technique with a high-speed video camera were conducted from the viewpoint of the unsteady flow features of the impinging jet. There exists a high-vorticity region at the jet boundary, resulting in the production of turbulence kinetic energy. In particular, higher vorticity is observed in the higher velocity side of the jet. The jet near the dome head has favorable characteristics about the flow rate distribution into the branched channel. Reynolds shear stress and turbulence energy are produced near the reattachment region. The jet has an oscillating motion near the dome head with asymmetric vortex formation at the jet boundary.

The Effect of the Bleed Hole Arrangement on Suppression of Swept Shock Wave/Turbulent Boundary Layer Interactions

The paper describes the experiments on the swept shock/boundary layer interactions with and without boundary layer bleed, as the fundamental research issue in the development of a supersonic air intake. The experiments were conducted in a supersonic wind tunnel with a cross section of 1 m by 1 m of the National Aerospace Laboratory. The emphasis was placed on understanding the flow structures of the interaction, using a shock generator with a 15 deg. wedge at Mach numbers of 3.25, 3.11 and 2.63. Attention was also focused on suppression of the interaction by a bleed system of hole arrangement. Three cases of the bleed system, where the bleed portions were located upstream, downstream, and in both regions of the swept shock wave, were employed. It was found by both Pitot-pressure rake and surface pressure survey methods, in addition to the vapor screen visualization technique, that the interaction becomes stronger with increasing Mach number. The arrangement of the bleed portion covering both upstream and downstream of the shock position is effective to suppress swept shock wave/boundary layer interactions.

Periodic Behavior of Longitudinal Vortices Downstream of an Active Vortex Generators Pair (Response of High Velocity Tongue to the Height of AVG and Development of Rotating X-array Hot-wire anemometer)

This paper is focused on the high velocity tongue beneath the longitudinal vortices downstream of a pair of active vortex generators (AVG) with common flow up configuration. An active control of turbulent boundary layer separation is one of the most interesting projects. It is important to achieve a smart control system based on the detailed information of time depended characteristics of the longitudinal vortices. Phase averaged mean velocity is measured by a newly developed rotating X-array hot-wire anemometer. The high velocity tongue shows rapid response to the height of the AVG at the final-stage of up-phase compared with the early-stage of down-phase. The transportation of high velocity fluid beneath the longitudinal vortices plays an important roll on the response of longitudinal vortices.

Flow Behavior in the Dump Diffuser Combustor With a Split Flow Effects of Inclined Wall in a Sudden Expansion Region

Recent aero-engine combustors have been of a large flame dome. The combustor diffuser wit h deep flame dome results in the large total pressure loss. It is important to obtain both better aerodynamics performance of the total pressure and exhaust gas characteristics of NOx in the combustor. Installation of an inclined wall within the dump diffuser combustor with a split flow at the flame dome head is suggested in order to improve the aerodynamic performance. The cold flow experiment in a model channel of the combustor diffuser conducted by the Laser Doppler Velocimetry system shows that the inclined wall is effective in improvement of the diffuser performance regardless of the ratio of the split flow rate. The key technology factor of inclined wall installation is the selection of the throat area ratio between the inclined wall and the flame dome.Copyright

Film Cooling Jet Aerodynamics for a Pipe and a Converging Nozzle Injection Hole

This paper presents the experimental study of film cooling jet aerodynamics for a pipe and a converging nozzle injection hole. The pipe jet has a fully developed velocity profile, and the nozzle jet has a top-hat one at the exit of the injection hole. The film cooling jet is injected into a turbulent boundary layer on a flat plate with 30° inclination angle. The mass flux ratio of the cooling jet to the primary flow is set at 0.8 and 1.2. Three components of mean velocity, vorticity and turbulent kinetic energy are measured using an X-array hot wire anemometer. The kidney vortex from the pipe jet is located closer to the wall than those from the nozzle jet. A tab is also installed at the exit of an injection hole to prevent the primary flow from convoluting. The effect of tab on the pipe jet is explicit.Copyright

Improvement of Aerodynamic Performance of a Combustor Dump Diffuser Using Inclined Walls

The combustor diffuser with the deep flame dome in the recent engine results in the large total pressure loss. It is important to obtain both better aerodynamic performance by reduction of total pressure loss and reduced NOx in the exhaust from the combustor, regardless of the inlet flow conditions such as inlet distortion. Installation of an inclined wall within the combustor dump diffuser is suggested in order to improve the aerodynamic performance. A cold flow experiment using Pitot probe surveys in a model of a combustor diffuser shows that the inclined wall is effective in improvement of the total pressure loss, even if the velocity profile at the diffuser inlet is distorted. Furthermore, the flow rate distributions into the branched channels are also improved. The flow mechanism in the inclined wall configuration is clarified from the measurements of the mean velocity and turbulent Reynolds stress by a Laser Doppler Velocimetry (LDV) system.Copyright

Effect of the Flame Dome Depth and Improvement of the Pressure Loss in the Dump Diffuser

This paper presents the effect of flame dome depth on the total pressure performance and flow behavior in a sudden expansion region of the combustor diffuser without flow entering the dome head. The mean velocity and turbulent Reynolds stress profiles in the sudden expansion region were measured by a Laser Doppler Velocitmetry (LDV) system. The experiments show that total pressure loss is increased, when flame dome depth is increased. Installation of an inclined combuster wall in the sudden expansion region is suggested from the viewpoint of a control of the reattaching flow. The inclined combustor wall is found to be effective in improvement of the diffuser performance. Better characteristics of the flow rate distribution into the branched channels are obtained in the inclined wall configuration, even if the distorted velocity profile is provided at the diffuser inlet.Copyright