Tip Injection Research Articles

Parametric study of injection from the casing in an axial turbine

Tip leakage flow reduces both efficiency and performance of axial turbines and damages turbine blades as well. Therefore, it is of great importance to identify and control tip leakage flow. This study investigated the effect of flow injection (from the casing), alongside flow structure, on turbine performance. Additionally, the effect of different injection parameters, including injection mass flow rate, angle, location, and diameter on the turbine performance are evaluated. A numerical analysis of the flow in a two-stage axial turbine was employed by using CFX software. To ensure the accuracy of the results, turbine performance curves were compared with the experimental results, which are in good agreement. Analyses revealed that active control method reduces tip leakage flow, improves turbine performance, and increases the efficiency by 1% to 5% as well. A parametric investigation of the tip injection has sought to identify how various parameters affect the turbine performance. The cross-section diameter and the angle of injection had no significant increase on efficiency. Additionally, results showed that at a point 9 mm further from the leading edge, the injection degree of effectiveness is optimum. Finally, analysis of the flow structure in the tip clearance region supported the tip leakage flow reduction.

Common source of light emission and nonlocal molecular manipulation on the Si(111)−7 × 7 surface

The tip of a scanning tunnelling microscope can inject hot electrons into a surface with atomic precision. Their subsequent dynamics and eventual decay can result in atomic manipulation of an adsorbed molecule, or in light emission from the surface. Here, we combine the results of these two near identical experimental techniques for the system of toluene molecules chemisorbed on the Si(111)−7 × 7 surface at room temperature. The radial dependence of molecular desorption away from the tip injection site conforms to a two-step ballistic-diffusive transport of the injected hot electrons across the surface, with a threshold bias voltage of +2.0 V. We find the same threshold voltage of +2.0 V for light emission from the bare Si(111)−7 × 7 surface. Comparing these results with previous published spectra we propose that both the manipulation (here, desorption or diffusion) and the light emission follow the same hot electron dynamics, only differing in the outcome of the final relaxation step which may result in either molecular displacement, or photon emission.

Numerical simulations and optimizations for turbine-related configurations

In order to accelerate the numerical simulation and optimization of gas turbine-related configurations, a source based computational fluid dynamics (SCFD) approach is developed for flow and heat transfer simulations. Different sources de-pending on the fluid porosity at each grid node in the computational domain are introduced to the continuity, momentum, energy and turbulence model equations, so that both the fluid and solid regions can be solved as one region. In the present paper, test cases including a ribbed channel and a winglet shrouded turbine cascade with tip injection are investigated using the SCFD and CFD with body-fitted meshes. Impacts of grid clustering and turbulence model equation sources on the SCFD precision are examined. Numerical results show that the SCFD predicts consistent aero-thermal performance with the fluid dynamics with body-fitted meshes and experiments. The validated SCFD scheme is then employed in a response surface optimization of tip jet holes on the winglet shroud tip. A jet arrangement with the minimum energy loss and injection mass-flow rate is obtained, indicating that source based predictions can be applied to the preliminary aero-thermal design of turbine blades.

Visualization of Flow Field in Circular Cascade Having Rotating Stall Suppressed by Tip Injection with PIV

Visualization of Flow Field in Circular Cascade Having Rotating Stall Suppressed by Tip Injection with PIV

Thermal performance of blade tip and casing coolant injection on a turbine blade with cavity and winglet-cavity tip

The heat transfer and film cooling effects of cavity tip and winglet-cavity tip have been numerically investigated with blade tip and casing coolant injection with a turbine cascade exit Ma number 0.96. The film-cooling effectiveness, heat transfer coefficient and net heat flux reduction ratio of blade tip and casing at relative tip clearance of 0.8% blade span are compared with blade tip cooling, casing purge cooling and the combination of these two cooling types. The validations and verifications of the numerical methods are performed by contrasting with the experimental results. The results show that the winglet-cavity tip alters the tip leakage flow and affects the heat transfer of blade tip compared to the cavity tip. For these two blade tip types, the blade tip cooling reduces the heat load of blade tip effectively, while it has little cooling effects on the casing. The casing purge cooling obtains high film-cooling effectiveness of the blade tip and the casing at the same time. However, it has no influence on the heat transfer of the pressure side near the tip region and the pressure-side rim. Adopting the blade tip and casing coolant injection simultaneously can further reduce the heat load and improve the film-cooling effectiveness of the blade tip and casing.

Influence of Rotor Tip Blockage on Near Stall Blade Vibrations in an Axial Compressor Rig

Rotor blade vibrations observed in the Darmstadt transonic compressor rig are investigated in this paper. The vibrations are nonsynchronous and occur in the near stall (NS) operating region. Rotor tip flow fluctuations traveling near the leading edge (LE) against the direction of rotation (in the rotor relative frame of reference) with about 50% blade tip speed are found to be the reason for the occurrence of the vibrations. The investigations show that the blockage at the rotor tip is an important factor for the aeroelastic stability of the compressor in the NS region. It is found that by application of a recirculating tip injection (TI) casing treatment, the aeroelastic stability increases as a result of reduced blockage in the rotor tip region.

Improvement of aerodynamic performance of a low speed axial compressor rotor blade row through air injection

This paper reveals that air injection at tip region of an axial compressor rotor blade row is an effective technique for enhancing its aerodynamic performance. Method of investigation is based on solution of the Navier–Stokes equations exploiting shear stress transport (SST) k–ω turbulence model. This model attempts to predict the turbulence by two partial differential equations for two variables of turbulence kinetic energy (k) and specific rate of dissipation (ω). Initially, computational performance curves of the proposed rotor blade row for no-injection case are compared with available experimental data, which show reasonable agreement. Then, effects of air tip injection on flow field and general aerodynamic performance of the rotor blade row are studied in detail. Results are presented in terms of the blade row span-wise distributions of total pressure rise coefficient and diffusion factor for no-injection and injection cases. Flow patterns at the blade row tip region are also carefully demonstrated. Six pseudo static pressure taps were mounted along the blade chord line within the blade tip gap region for detection of the flow fluctuations. So, it was possible to extract frequency spectrum of the fluctuating flow in this region. Numerical simulations confirmed that injection of air flow at the blade row tip region boosts the flow momentum and reduces blockages due to the flow separation from the blades surfaces. Results showed that air injection as small as of only 0.5% of the whole annulus mass flow rate causes the stall margin of the rotor blade row to increase by 15.5%.

The role of angled-tip microcatheter and microsphere injection velocity in liver radioembolization: A computational particle-hemodynamics study.

Liver radioembolization is a promising treatment option for combating liver tumors. It is performed by placing a microcatheter in the hepatic artery and administering radiation-emitting microspheres through the arterial bloodstream so that they get lodged in the tumoral bed. In avoiding nontarget radiation, the standard practice is to conduct a pretreatment, in which the microcatheter location and injection velocity are decided. However, between pretreatment and actual treatment, some of the parameters that influence the particle distribution in the liver can vary, resulting in radiation-induced complications. The present study aims to analyze the influence of a commercially available microcatheter with an angled tip and particle injection velocity in terms of segment-to-segment particle distribution. Specifically, 4 tip orientations and 2 injection velocities are combined to yield a set of 8 numerical simulations of the particle-hemodynamics in a patient-specific truncated hepatic artery. For each simulation, 4 cardiac pulses are simulated. Particles are injected during the first cycle, and the remaining pulses enable the majority of the injected particles to exit the computational domain. Results indicate that, in terms of injection velocity, particles are more spread out in the cross-sectional lumen areas as the injection velocity increases. The tip's orientation also plays a role because it influences the near-tip hemodynamics, therefore altering the particle travel through the hepatic artery. However, results suggest that particle distribution tries to match the blood flow split, therefore particle injection velocity and microcatheter tip orientation playing a minor role in segment-to-segment particle distribution.

Experimental and numerical study of tip injection in a subsonic axial flow compressor

Parametric study of tip injection was implemented experimentally on a subsonic axial flow compressor to understand the underlying flow mechanisms of stability improvement of the compressor with discrete tip injection. Injector throat height varied from 2 to 6 times the height of rotor tip clearance, and circumferential coverage percentage ranged from 8.3% to 25% of the annulus. Static pressure fluctuations over the rotor tip were measured with fast-response pressure transducers. Whole-passage time-accurate simulations were also carried out to help us understand the flow details. The combinations of tip injection with traditional casing treatments were experimentally studied to generate an engineering-acceptable method of compressor stall control. The results indicate that the maximum stability improvement is achieved when injectors are choked despite their different sizes. The effect of circumferential coverage percentage on compressor stability depends on the value of injector throat height for un-choked injectors, and vice versa. Tip blockage in the blade passage is greatly reduced by the choked injectors, which is the primary reason for stability enhancement. The accomplishment of blockage diminishment is maintained in the circumferential direction with the unsteady effect of tip injection, which manifests as a hysteresis between the recovery of tip blockage and the recovery of tip leakage vortex. The unsteady effect is primarily responsible for the effectiveness of tip injection with a partial circumferential coverage. Tip injection cannot enhance the stability of the rotor with axial slots significantly, but it can improve the stability of the rotor with circumferential grooves further. The combined structure of tip injection with circumferential grooves is an alternative for engineering application.

Performance Enhancement of a Low Speed Axial Compressor Utilizing Simultaneous Tip Injection and Casing Treatment of Groove Type

Performance of a low speed axial compressor is enhanced through a proper configuration of blade row tip injection and casing treatment of groove type. Air injectors were mounted evenly spaced upstream of the blade row within the casing groove and were all aligned parallel to the compressor axis. The groove, which covers all the blade tip chord length, extends all-round the casing circumference. Method of investigation is based on solution of the unsteady form of the Navier-Stokes equations utilizing k-ω SST turbulence model. Extensive parametric studies have been carried out to explore effects of injectors’ flow momentums and yaw angles on compressor performance, while being run at different throttle valve setting. Emphasis has been focused on situations near to stall condition. Unsteady numerical analyses for untreated casing and no-injection case for near stall condition provided to discover two well-known criteria for spike stall inception, i.e., blade leading edge spillage and trailing edge back-flow. Final results showed that with only 6 injectors mounted axially in the casing groove and at yaw angle of 15 degrees opposite the direction of the blade row rotation, with a total mass flow rate of only 0.5% of the compressor main flow, surprisingly, the stall margin improves by 15.5%.

Experimental investigation on flow unsteadiness during spike stall suppression process in an axial compressor via air injection

Stall recovery process for performance enhancement of an axial compressor has been experimentally carried out using air injection at its rotor blade row tip region. Twelve air injectors had been mounted evenly spaced around the compressor casing upstream the rotor blade row. Instantaneous flow velocities at various radial and circumferential positions were measured simultaneously utilizing hot wire anemometry. These unsteady results, separately presented in frequency and time domains, provided to distinguish stall inception process and consequent flow induced fluctuations. Time-dependent responses of the flow field properties within the compressor passage and progressive alleviation of stall cells are demonstrated during the tip injection process. Blade tip air injection worked effectively and enhanced the compressor stall margin about 9%. This attractive result occurred for the case where the total mass flow rate passing through the air injectors was as small as 0.8% of the compressor main flow rate. In addition, this augmentation in the stall margin was accompanied by increase in the compressor delivery total pressure. Air injection at the blade row tip region caused its beneficial effects to extend throughout the blade whole span, especially while working at the near-stall conditions.

Liquid fertilizer application to ratoon cane using a soil punching method

Sugarcane is a semi-perennial crop that is cultivated for five or six harvest cycles before replanting. Following annual mechanized harvest, nitrogen (N) fertilizer is commonly applied during the ratoon cane sprouting phase through furrows along the side of plant rows (subsurface application) or banded on the surface. With subsurface application, mechanical operations are hampered by the trash coverage that remains after harvest; furthermore, opening furrows can partially damage roots. However, with soil surface application, nutrient uptake efficiency is decreased as a result of microbial immobilization and losses through ammonia volatilization and runoff. Thus, to achieve subsurface application for ratoon cane with minimal mobilization of the system (soil, straw and roots), this work aimed to (i) develop and evaluate a mechanical prototype that enables a soil punching process in ratoon cane and (ii) evaluate the cane yield using the soil punching method for liquid N fertilizer injection compared to liquid N fertilizer applied alongside of plant rows on the surface and subsurface (through furrows). To evaluate the punching mechanism, we performed a kinematic simulation (puncher tip displacement and injection time interval), tests in a soil bin and ratoon cane field. Based on prototype operations, the average distance between applications was 300mm, with an average depth up to 90mm, which was similar to the design requirements. Regarding results of liquid N fertilization methods in a ratoon cane field, we found that the incorporation treatments (soil punching and subsurface application through furrows) achieved slightly better cane yield (98–96Mgha−1) when compared to the surface application (91Mgha−1) and control treatment (75Mgha−1). In general, the soil punching was considered as a promising alternative method for supplying liquid fertilizer at the subsurface using low-energy power (approximately 745W) with minimal environmental impact.

Performance Enhancement of Centrifugal Compressors Utilizing Impeller Tip Injection

AbstractEffects of air injection on a centrifugal compressor performance are studied numerically and results are presented in this paper. Flow field is simulated based on solution of the Reynolds-Averaged Navier-Stokes equations utilizing the well-known k-ε turbulence modeling. To find optimum arrangement of the air injectors, including their numbers, positions and setting angles and also their mass flow rates, 10 different cases were proposed in this investigation. Results of velocity and pressure fields and streamlines patterns on various blade-to-blade and streamwise planes provided necessary data for analyses and discussions. These results revealed that a proper air tip injection can weaken the tip leakage flow strength and alleviate the blockages to the main stream near the casing. Hence, this technique can be used to extend the stable operating range of the compressor and delay the probable stall commencement. In addition, compressor can produce higher pressure ratios in cases of proper injections in comparison to no-injection case. Optimum injection configuration improved the stall margin of the proposed compressor by nearly 15.8%. Numerical results for no-injection case were compared with those of the authors own experimental works carried out on a proper test rig, which showed close agreement.

Turbine Blade Tip Film Cooling With Blade Rotation—Part I: Tip and Pressure Side Coolant Injection

An experimental study of film cooling is conducted on the tip of a turbine blade with a blade rotation speed of 1200 rpm. The coolant is injected from the blade tip and pressure side (PS) holes, and the effect of the blowing ratio on the heat transfer coefficient and film cooling effectiveness of the blade tip is investigated. The blade has a tip clearance of 1.7% of the blade span and consists of a cut back squealer rim, two cylindrical tip holes, and six shaped PS holes. The stator–rotor–stator test section is housed in a closed loop wind tunnel that allows for the performance of transient heat transfer tests. Measurements of the heat transfer coefficient and film cooling effectiveness are done on the blade tip using liquid crystal thermography. These measurements are reported for the no coolant case and for blowing ratios of 1.0, 1.5, 2.0, 3.0, and 4.0. The heat transfer result for the no coolant injection shows a region of high heat transfer on the blade tip near the blade leading edge region as the incident flow impinges on that region. This region of high heat transfer extends and stretches on the tip as more coolant is introduced through the tip holes at higher blowing ratios. The cooling results show that increasing the blowing ratio increases the film cooling effectiveness. The cooling effectiveness signatures indicate that the tip coolant is pushed toward the blade suction side thereby providing better coverage in that region. This shift in coolant flow toward the blade suction side, as opposed to the PS in stationary studies, can primarily be attributed to the effects of the blade relative motion.

Role of tip injection in desensitizing the compressor to the tip clearance size

Numerical simulations are performed to investigate the role of tip injection in desensitizing a transonic compressor rotor to the detrimental effects of tip leakage flow. First, the effects of tip clearance size on the compressor stability and performance are investigated. Endwall injection of high-speed fluid upstream of the blade is then applied to the compressor with different tip clearance sizes. Results reveal that tip injection can effectively desensitize the compressor stability to the tip clearance size and improve the total pressure ratio, at the expense of some efficiency loss. It is further found that the larger the tip clearance size, the greater the stability enhancement and the smaller the efficiency penalty due to injection. The near-stall endwall flow structures for different tip clearance sizes, with and without injection, are also investigated in the current study. Results suggest that tip clearance size does not influence the compressor stalling mode, whereas endwall injection has the potential to change it (i.e., from “wall-stall” to “blade-stall” with the injection applied in the current study).

Effects of tip injection on the performance and near wake characteristics of a model wind turbine rotor

This paper presents an investigation of the effects of tip injection on the performance and near wake characteristics of a model wind turbine rotor. Experiments are conducted by placing a three-bladed horizontal axis wind turbine rotor at the exit of an open-jet wind tunnel. The rotor blades are non-linearly twisted and tapered with NREL S826 airfoil profile. The nacelle, hub and the blades are specifically designed to allow pressurized air to pass through and get injected from the blade tips while the rotor is rotating. Measurements of torque and thrust coefficient variations with the Tip Speed Ratio (TSR) as well as wake flow field surveys using Constant Temperature Anemometry are performed with and without tip injection. Results show that power and thrust coefficients both increase due to injection especially at TSR values higher than 3.5. Wake characteristics show a tip flow region that is radially pushed outwards with increased levels of turbulence occupying wider areas compared to the no-injection case. Up to two diameters downstream within the wake, the boundary between the wake and the freestream, which is normally dominated by the presence of the tip vortices, gets more diffused and turbulence levels are significantly increased due to tip injection.

An experimental investigation of the combined influence of notch size and fibre orientation on the fatigue strength of a short glass fibre reinforced polyamide 6

An experimental study of the fatigue strength of injection moulded short fibre reinforced polyamide plates is presented, which investigated the combined effect of notch tip radius and injection gate position on injection moulded specimens. Fatigue tests were conducted on samples having two symmetric V-shaped notches, with a fillet radius varying from 0.5 to 2 mm. The injection moulding conditions and resulting fibre orientation distribution were varied by injecting the plates longitudinally and laterally. For the same type of injection gate, the influence of the notch root radius appeared to be negligible, with the exception of the smallest radius which had a lower strength. Measurements of fibre orientation showed that the smallest radius modified the local fibre structure, and fatigue crack growth observations showed that the crack propagation phase become dominant with the smallest radius.

Aerodynamic performance of transonic axial compressor with a casing groove combined with blade tip injection and ejection

Blade tip ejection was introduced to a casing groove combined with tip injection in a transonic axial compressor with NASA Rotor 37. A parametric study of compressor performances was performed using three-dimensional (3-D) Reynolds-averaged Navier–Stokes equations with the k–ϵ turbulence model. Effects of three geometric parameters and one operating parameter, i.e., the front and rear lengths and height of the casing groove, and the mass flow rate of groove ejection, on the performance parameters, i.e., the total pressure ratio, adiabatic efficiency, stall margin, and stable range extension, were investigated in the parametric study. The application of a casing groove combined with tip injection and ejection was found to be effective in the simultaneous improvements of adiabatic efficiency, stall margin, and stable range extension without loss of the total pressure ratio of the transonic axial compressor, compared to the case with a casing groove with injection only, and a smooth casing.

Effects of camberwise varying tip injection on loss and wake characteristics of a low pressure turbine blade

This paper presents the results of an experimental study that investigates the effects of camberwise varying tip injection on the total pressure loss and wake flow characteristics downstream of a row of Low Pressure Turbine (LPT) blades. This injection technique involves spanwise jets at the tip that are issued from a series of holes distributed along the camber line. The injection from each hole is individually and separately controlled using a computer driven solenoid valve and therefore the flow injection geometrical pattern at the tip can be adjusted to any desired variation. Three different injection cases are investigated including triangular, reversed triangular and uniform injection patterns. Here, triangular and reversed triangular cases refer to discrete blowing from the blade tip in which the blowing velocity increases (triangular) or decreases (reverse triangular) linearly from the leading to trailing edge along the camber. For uniform injection, the injection velocity is kept constant for all injection holes. The total mass injection from the tip is kept the same for all injection cases. The experiments are conducted in a continuous-flow wind tunnel with a linear cascade test section and measurements involve Kiel probe traverses 0.5 axial chords downstream of the blades covering a region between 85% and 100% span as well as two-dimensional Particle Image Velocimetry (PIV) measurements on 50%, 85% and 95% spanwise planes. For all injection cases, results show that tip injection reduces the total pressure loss levels in general. Highest measured overall loss reduction occurs in the case of reversed-triangular injection. The least effective waveform is observed to be triangular injection. There is significant reduction in the extent of the low momentum zone of the leakage vortex with injection. This effect is much less pronounced for the passage vortex. On the other hand, complex flow patterns are observed within the passage vortex, especially in the case of reversed-triangular injection, such as a possible embedded vortical structure along the passage vortex core, which creates double peaks in the velocity and turbulent kinetic energy fields.

High Resolution RANS Nonlinear Harmonic Study of Stage 67 Tip Injection Physics

Numerical prediction of the Stage 67 transonic fan stage employing wall jet tip injection flow control and study of the physical mechanisms leading to stall suppression and stability enhancement afforded by endwall recirculation/injection is the focus of this paper. Reynolds averaged Navier–Stokes (RANS) computations were used to perform detailed analysis of the Stage 67 configuration experimentally tested at NASA's Glenn Research Center in 2004. Time varying predictions of the stage plus recirculation and injection flowpath were executed utilizing the nonlinear harmonic (NLH) approach. Significantly higher grid resolution per passage was achieved than what has been generally employed in prior reported numerical studies of spike stall phenomena in transonic compressors. This paper focuses on characterizing the physics of spike stall embryonic stage phenomena and the influence of tip injection, resulting in experimentally and numerically demonstrated stall suppression.