Slot Injection Research Articles

Non-uniform double slot injection (suction) on a forced flow over a slender cylinder

A general analysis has been developed to investigate the influence of non-uniform double slot injection (suction) on the steady non-similar incompressible laminar boundary layer flow over a slender cylinder, where the slender cylinder is inline with the flow. Non-similar solutions are obtained starting from the origin of the stream-wise coordinate along the stream-wise direction by using an implicit finite difference scheme in combination with the quasilinearization technique. Numerical results are reported to display the effects of non-uniform double slot injection/suction on skin friction coefficient and heat transfer rate at the wall. Further, the effects of viscous dissipation and Prandtl number on velocity and temperature profile, and skin friction and heat transfer co-efficients are also presented in this paper.

衝撃波の入射位置が壁面燃料噴射場における燃焼と流れ場に及ぼす影響

Experimental and numerical studies of the interaction between combustion of a hydrogen jet and an incident shock wave were performed. In the case that an incident shock wave was introduced upstream of the injection slot, the boundary-layer separation region was extensively expanded. The penetration height of the Mach disk with an incident shock wave was less than that without an incident shock wave. Combustion was confirmed when the incident shock wave was introduced downstream of the fuel injection slot, while, with the incident shock wave upstream of fuel injection slot, combustion was not confirmed. The mechanism of these phenomena was discussed based on the results of numerical simulation in terms of the residence time in the separation region near the fuel injection slot.

粒子追跡速度計法を用いた壁面噴射場と衝撃波の干渉現象の研究

An experimental study was performed to investigate the flame-holding of hydrogen jet injected into supersonic cross-flow interacting with an incident shock wave. Pre-burned rich hydrogen or air was injected in supersonic airflow at Mach 2.5. The injection pressure was 1.2MPa or 1.6MPa. The deflection angle of the shock generator was 10 deg. Velocity profiles near the wall and those of recirculation zones around the injection slot could successfully be measured using newly-devised PTV method in this study. The velocity profiles showed that re-attachment point of separation downstream of the injection slot moves downstream when the incident shock wave is introduced to downstream of the injection slot. The re-attachment point with the incident shock wave in case of the injection pressure of 1.6MPa was not so different from that of 1.2MPa. However, extinction limit in case of the injection pressure of 1.6MPa extended than that of 1.2MPa.

Non-uniform mass transfer or wall enthalpy into a compressible flow over a rotating sphere

A study for the effect of non-uniform slot injection/suction and non-uniform total enthalpy at the wall for a steady non-similar laminar compressible boundary layer flow over a rotating sphere is presented. The effects of rotation and free stream Mach number have also been considered. Non-similar solutions have been obtained from the starting point of the stream wise coordinate to the point of separation using an implicit finite difference scheme in combination with the quasi-linearization technique. The results indicate that the separation can be delayed by non-uniform slot suction and also by moving the slot downstream but the non-uniform slot injection has just the opposite effect. An increase of rotation and total enthalpy at the wall causes separation to occur earlier while cooling delays it. An increase of the Mach number shifts the point of separation upstream due to the adverse pressure gradient. The non-uniform total enthalpy at the wall has a very little effect on the skin friction and hence on the point of separation.

Numerical Modelling of Design Parameters for Manufacturing Polyester/Glass Composites by Resin Injection Pultrusion

Resin Injection Pultrusion (RIP) is an automated, continuous process and is one of the most cost-effective methods for manufacturing composite materials with constant cross sections (such as rod stock, beams, channels and tubing). In the present work, a 3-D finite volume technique was developed to advance the liquid resin flow front through the fibre reinforcement in the injection pultrusion process. The objective of this study was to improve fibre reinforcement wet-out and thus the quality of the pultruded part in an injection pultrusion process. The complete wet-out of the dry reinforcement by the liquid resin depends on various design and process parameters. The design parameters explored in this study were the aspect ratio of the final composite, injection slot width, injection slot location from inlet of injection chamber, and location of the multiple injection ports. The numerical model simulates the flow of polyester resin through glass rovings and predicts the impact of the design (geometric) parameters on wet-out, resin pressure field, and resin velocity field. The location of the liquid resin flow front has been predicted for an injection slot, as well as for five discrete injection ports.

Manufacturing Modeling of Three-Dimensional Resin Injection Pultrusion Process Control Parameters for Polyester/Glass Rovings Composites

Pultrusion, sometimes referred to as continuous resin transfer molding process, is a continuous, cost-effective method for manufacturing composite materials with constant cross sections (such as rod stock, beams, channels, and tubing). The objective of this study is to improve the fiber reinforcement wetout and thus the quality of the pultruded part in the injection pultrusion process. The complete wetout of the dry reinforcement by the liquid resin depends on various design and process parameters. The process parameters modeled in this study are fiber pull speed, fiber volume fraction, and viscosity of the resin. In the present work, a three-dimensional finite volume technique is employed to simulate the liquid resin flow through the fiber reinforcement in the injection pultrusion process. The numerical model simulates the flow of polyester resin through the glass rovings and predicts the impact of the process parameters on wetout, resin pressure field, and resin velocity field. The location of the liquid resin flow front has been predicted for an injection slot as well as for five discrete injection ports.

Effect of Injection Slot Size on the Performance of Coflow Jet Airfoil

Two coflowjet airfoils with injection slot size differing by a factor of 2 are tested in a wind tunnel to study the effect of injection slot size. At the same angle of attack, the larger injection slot size airfoil passes about twice the jet mass flow rate of the smaller injection slot size airfoil. The smaller injection slot size airfoil is more effective in increasing the stall margin and maximum lift, whereas the larger slot coflow jet airfoil is more effective in reducing drag. To achieve the same lift, the smaller injection slot size airfoil has much less energy expenditure than the larger injection slot airfoil. A coefficient of jet kinetic energy is introduced, which appears to correlate well with the maximum lift and stall margin when coflow jet airfoil geometry varies. Both the jet kinetic energy coefficient and the momentum coefficient correlate well with drag reduction. No optimization of the airfoil configuration is pursued in this research, and the results indicate that there is a great potential for coflow jet airfoil performance improvement.

Influence of bubble size on micro-bubble drag reduction

Micro-bubble drag reduction experiments were conducted in a turbulent water channel flow. Compressed nitrogen was used to force flow through a slot injector located in the plate beneath the boundary layer of the tunnel test section. Gas and bubbly mixtures were injected into a turbulent boundary layer (TBL), and the resulting friction drag was measured downstream of the injector. Injection into tap water, a surfactant solution (Triton X-100, 20 ppm), and a salt-water solution (35 ppt) yielded bubbles of average diameter 476, 322 and 254 μm, respectively. In addition, lipid stabilized gas bubbles (44 μm) were injected into the boundary layer. Thus, bubbles with d+ values of 200 to 18 were injected. The results indicate that the measured drag reduction by micro-bubbles in a TBL is related strongly to the injected gas volumetric flow rate and the static pressure in the boundary layer, but is essentially independent of the size of the micro-bubbles over the size range tested.

Experimental investigation of airfoil trailing edge heat transfer and aerodynamic losses

Modern gas turbine development is being driven by the often-incompatible goals of increased efficiency, better durability, and reduced emissions. High turbine inlet temperatures and ineffective cooling at the trailing edge of a first-stage stator vane lead to corrosion, oxidation, and thermal fatigue. Observations of this region in engines frequently reveal burn marks, cracks, and buckling. Fundamental studies of the importance of trailing edge heat transfer to the design of an optimal cooling scheme are scarce. An experimental study of an actively cooled trailing edge configuration, in which coolant is injected through a slot, is performed. Trailing edge heat transfer and aerodynamic measurements are reported. An optimum balance between maximizing blade row aerodynamic efficiency and improving thermal protection at the trailing edge is estimated to be achieved when blowing ratios are in the range between 2.1% and 2.8%. The thermal phenomena at the trailing edge are dominated by injection slot heat transfer and flow physics. These measured trends are generally applicable over a wide range of gas turbine applications.

Effect of non-uniform slot injection (suction) on a forced flow over a slender cylinder

An analysis is performed to obtain the non-similar solution of a steady laminar forced convection boundary layer flow over a horizontal slender cylinder including the effect of non-uniform slot injection (suction). The effects of transverse curvature and viscous dissipation are also included in the analysis. The governing boundary layer equations along with the boundary conditions are first cast into a dimensionless form using suitable transformations and the resulting system of nonlinear coupled partial differential equations is then solved by an implicit finite difference scheme in combination with the quasilinearization technique. Numerical results for the effect of non-uniform slot injection (suction) on skin friction coefficient and heat transfer rate are presented. The effects of transverse curvature, viscous dissipation and Prandtl number on velocity and temperature profiles and skin friction and heat transfer coefficients are also reported.

スリット噴射による二次元超音速混合流れ場における噴射角の与える影響

Experimental and computational studies on supersonic mixing by slotted injection with various injection angle have been conducted. In the experiment flat plate model is installed into supersonic free stream of Mach number of 4 and fully developed turbulent boundary layer is established on the flat plate. The secondary jet is injected through slot nozzle set on the flat plate model in order to simulate SCRAM-jet supersonic mixer. Experiments are conducted by changing injection angle of helium gas in order to observe the effect of injection angle to the supersonic mixing. The flow fields are visualized by the Schulieren method. Also surface pressure distributions and spatial distributions are measured. The same flow fields are simulated by solving tow-dimensional full Navier-Stokes equation of mixture gas of air and helium and calculated results are compared with experiments. Quite good agreement is obtained in wall pressure distributions. And qualitative agreement is obtained in volume fruction distribution. By using the calculated results, the correlations between the mixing rate and the total pressure loss of the flow field are obtained.

Parameters Affecting Turbulent Film Cooling-Reynolds-Averaged Navier-Stokes Computational Simulation

Film cooling of surfaces appears in many applications. For instance, it is one of the most effective methods to improve the efficiency of gas turbines. As a fundamental study, two different types of film cooling (slot and discrete holes injections) are numerically simulated here. A flat surface is used to model a small portion of a gas turbine blade. Incompressible, stationary, viscous, turbulent flow is assumed using the STAR-CD software with the standard k‐e model and a cell-centered finite volume method on a nonuniform structured grid. The jet flow Reynolds number, based on the jet’s hydraulic diameter, is 4.7 × × 103. The study of the injection angle and the velocity ratio shows that the optimum film cooling occurs at jet angle of about 30 deg. However, the optimal velocity ratios of about 1.5 for slot injection and about 0.5 for discrete holes injection have been obtained. On the other hand, the study of jet-exit aspect ratio in discrete holes injection shows that stretching the hole in spanwise direction increases the film-cooling effectiveness. Also, the study of jet spacing in spanwise direction shows that decreasing the jet spacing increases the film-cooling effectiveness, but not as much as the jet aspect ratio.

Numerical Investigation of Flow Control by Suction and Injection on a Subsonic Airfoil

This study presents a numerical study concerning flow control by suction and injection. The case studied is the flow field over a subsonic airfoil with four suction and injection slots on the suction side of the airfoil. Five different angles of attack, 0, 5, 10, 13.3 and 20 with the Mach number of 0.15 are studied. Three cases are studied in each angle of attack. The three cases are airfoil with surface suction, surface injection and the base airfoil. A commercial CFD code, the FLUENT, is used in this study. The effect of suction and injection on aerodynamic coefficients is investigated. The results show that the surface suction can significantly increase the lift coefficient. The injection decreases the skin friction.

Modeling study of shrouding gas effects on a laminar argon plasma jet impinging upon a flat substrate in air surroundings

With the laminar plasma materials processing as the research background, modeling study is conducted concerning the effects of argon shroud on the characteristics of the laminar argon plasma jet impinging normally upon a flat substrate located in air surroundings. It is shown that adding shrouding gas is an effective method to reduce and control the entrainment of ambient air into the laminar plasma jet. The shrouding gas flow rate or velocity, the injection slot width and the stand-off distance of the substrate appreciably affect the air contents in the plasma near the substrate surface.

Characterization of Steady Blowing for Flow Control in a Hump Diffuser

A study has been performed to characterize the effects of steady boundary-layer injection on the separated flow of a hump diffuser. Results of parametrically varying discrete hole blowing characteristics have identified two separate regimes where the injection momentum coefficient and velocity ratio, respectively, are the primary scaling parameters for pressure recovery. Both discrete hole and slot injection have been investigated for varying degrees of adverse pressure gradient in the streamwise direction, indicating optimal discrete hole injection to be more efficient than slot injection in terms of necessary injection momentum coefficient to achieve maximum levels of increased pressure recovery. The effects of discrete injection parameters such as hole diameter, hole spacing, and streamwise injection (yaw) angle have been studied. Angled injection (45-deg yaw) has been shown to be most effective in removing separated flow and increasing the pressure recovery. The angled injection enhances shear layer mixing through large-scale corotating vortical motion induced by the yawed jet-main flow interaction. A computational fluid dynamics/data comparison study has been performed on the results of the discrete injection tests, capturing overall data trends and representing the net effect of streamwise and angled injection on pressure recovery in the hump diffuser.

Suppression of Premature Ignition in the Premixed Inlet Flow of a Shcramjet

This paper addresses the problem of premature ignition in a shock induced combustion ramjet (shcramjet) inlet. Previous studies have developed fuel injectors and inlet configurations that maximize the mixing efficiency in a shcramjet inlet while maintaining inlet losses at a minimum. A chemically reacting study of previously recommended shcramjet inlets finds premature ignition to occur primarily in the boundary layer in the last 15% of the inlet, spreading into the core flow prior to the inlet exit. Both gaseous nitrogen and additional hydrogen are then injected into the inlet flowfield in an attempt to suppress the flame. Various inflow conditions are considered, and injected using various geometries. Premature ignition is suppressed most feasibly by the injection of additional hydrogen through a backward facing step (slot injector) located just before the second inlet shock, such that the global equivalence ratio of the premixed flow exiting the inlet is one. The performance of the original inlet remains unaltered and the frictional force on the inlet wall is reduced by 10% due to the hydrogen slot injection. All turbulent, chemically reacting, three dimensional, mixing flowfields are solved using the WARP code which solves the FANS equations closed by the Wilcox kω turbulence model and the Wilcox dilatational dissipation correction. Chemical kinetics are modeled by a 9 species, 20 reaction model by Jachimowski.

F224 超薄型タービン翼の二次元膜冷却による断熱特性(一般セッション 熱伝達)

This experimental work is to investigate film cooling for slot injection into a separated region of very thin turbine blade. The purpose of this research is to clarify the feasibility of the turbine blade which has been thinned the thickness. With such a thin turbine blade, as flow separation occur on the pressure-side, so film cooling practice in that kind of flow filed has not been well established. The experimental results showed: followings a reattachment length is about five times step height. Characteristic of adiabatic effectiveness in the pressure-side wall depends not only blowing ratio but also situation of a separated shear layer and shape of turbine blade.

Non-uniform slot injection (suction) into water boundary layer flow past yawed cylinder

The non-uniform slot injection (suction) into water boundary layer flow over a yawed infinite circular cylinder is analyzed including the temperature-dependent viscosity and Prandtl number. The difficulties arising at the starting point of the streamwise coordinate, at the edges of the slot and at the point of separation are overcome by applying the implicit finite difference scheme in combination with the quasilinearization technique. The results indicate that the separation can be delayed by non-uniform slot suction and also by moving the slot downstream but effect of non-uniform slot injection is just the opposite. Further, the effect of variable fluid properties is to move the point of separation downstream but yaw angle has very little affect on the location of the point of separation.

Statistical analysis of high-order moments in a turbulent boundary layer with large density gradients

An experimental study of the effects of large density variations on the turbulent transfers in a boundary layer is carried out in this paper. Density differences were generated by tangential injection of air or helium in a mixture of these two components. In order to study the fine structure of wall turbulence in the presence of significant density variations, a statistical analysis of the experimental data, obtained in a wind tunnel, is carried out. The results show that the relaxation of the skewness factor of u′(Su′) is carried out more quickly in the external layer than close to the wall, for the air injection as well as for the helium injection. Su′ grows close to the injection slot in an appreciable way, and this increase definitely is stronger for the air injection than for the helium injection. This growth of the skewness factor close to the injection slot can be explained by the increase in the longitudinal convective flux of turbulent energy in this zone. For the distributions of the flatness factor Fu′ the results show that there is no significant effect of the density gradient on the intermittent structure of the instantaneous longitudinal velocity in the developed zone, x/δ≥5, where δ is the boundary-layer thickness. Differences remain, of course, between the profiles of Fu′ for density gradients Open image in new window in the relaxation zone, where the longitudinal gradients are significant. It should, however, be noted that Open image in new window has a smaller effect on the flatness factor compared to the skewness factor. The statistical analysis carried out in this study shows that the helium injection in the boundary layer generates more violent ejections than the air injection. This result is confirmed by the significant contribution of the ejections to turbulent mass flux.

On the control of laminar flow separation

Laminar flow separation readily occurs when fluid flows past an obstacle at high Reynolds number. Control of separation can be exercised by, for example, suction at the boundary or suitable slot injection. In this paper we demonstrate that if a circular cylinder, placed in a uniform stream, performs suitable very small amplitude oscillations, at a very high frequency, then flow separation may be delayed and even prevented altogether.