Tip Injection Research Articles

Stall inception and control in a transonic fan, part B: Stall control by discrete endwall injection

This paper reports on a half-annulus numerical investigation of discrete tip injection in a transonic compressor rotor. The effect of injection on controlling stalling disturbances is investigated by activating endwall injection at an in-stall condition, caused by an enlarged-tip blade. Furthermore, choke to stall time-accurate computations have been carried out in order to study the effect of discrete injection on extending the stable operating range. Investigating the near-stall condition with injection reveals that the occurrence of the time-averaged leading-edge vortex spillage is the key path to stall inception, similar to the smooth casing. Nonetheless, when tip injection is discrete, limited instantaneous vortex spillage can occur over the leading edge of the blades approaching the injector.

The Dual Mechanisms and Implementations of Stability Enhancement With Discrete Tip Injection in Axial Flow Compressors

The mechanisms and implementation scheme of discrete tip air injection are studied in this paper. A map that summarized the routes to stall is then proposed. It is argued that there exists a critical tip clearance ratio that separates two different routes to stall, which infers that the stability enhancement can also be based on two different mechanisms. A summation of tip injection test data in the literatures demonstrates that this is actually the case. For each compressor, there are two trends in the curve of stall margin improvement (SMI) versus injected momentum ratio, which is separated by a demarcation ratio of injected momentum. A series of tests are done in a low-speed compressor to show that the micro injection, wherein the injected momentum ratio is less than the demarcation ratio, can only act on the tip leakage flow (TLF) and thus provide small SMI by weakening the self-induced unsteadiness of the tip leakage flow (UTLF), while in contrast the macro injection can provide much larger SMI by acting on the main flow, decreasing the inlet angle-of-attack and thus unloading the blade tip. Based on these findings, a novel detecting-actuating scheme is designed and implemented onto a low-speed axial compressor. A cross-correlation coefficient is used to detect the UTLF in the prestall process way before stall inception and then to guide the opening of proportional electromagnetic valves. The injected flow rate can be smoothly varied to cover both micro- and macro-injection, which saves energy when the compressor is stable, and provides protection when it is needed. The same principle is applied to a high-speed compressor with a recirculation injection and the preliminary test results are very encouraging.

Local Anesthetics: What's New in Minimal Pain Injection and Best Evidence in Pain Control.

Local anesthesia in plastic surgery is undergoing a revolution. In the last 10 years, significant improvements in technique have permitted surgeons to do more and more under pure local anesthesia to increase patient safety and convenience while maintaining total patient comfort during the injection of the local anesthesia and while the procedure is accomplished. Many procedures which used to require sedation are now being performed without it. This article explores some of the new advances in local anesthesia such as painless blunt-tipped cannula local anesthetic infiltration, decreased pain with sharp needle tip injection, and long-lasting local anesthetics with delayed release from liposomal encapsulation. This article also examines the best evidence of the last 10 years of advances of pain control with local anesthesia.

Control of Tip Leakage Vortex Breakdown by Tip Injection in Unshrouded Turbines

Tip leakage flow is responsible for a number of aerodynamic losses in turbines, but the leakage loss mechanisms have not been fully elucidated yet. This paper computationally investigates the effects of tip injection on tip leakage vortex dynamics in an unshrouded turbine, in an attempt to seek new loss generation mechanisms in turbine tip clearance flows and to influence them by the injection. First, a linear cascade validation is introduced, and the computations are compared with the experimental data to identify the ability of computational fluid dynamics code to predict the tip leakage flow. The tip leakage vortex breakdown phenomenon and dynamics analysis are shown, and then the effects of tip injection on leakage vortex structure and vortex breakdown characteristics are investigated. Also, the effect of leakage vortex breakdown on aerodynamic performance of the turbine with injection is examined. Results indicate that the leakage vortex breakdown occurs when the pressure rise is large enough in the rear part of the blade suction side near the tip, and it is an important loss mechanism associated with tip leakage. Injection location has a different impact on the leakage vortex dynamics, dependent on the tip pressure field characteristics. With injection in the front part, the leakage vortex breakdown is delayed, where the turbine achieves the best performance improvement, and the vortex breakdown location moves downstream as the injection mass flow rate increases.

Reduction of turbine tip clearance losses at design and off-design incidences by non-uniform tip injection

Tip injection has shown potential for controlling turbine tip clearance flows; however, the effects of tip injection may behave differently at design and off-design incidences. This paper computationally investigates the sensitivity of endwall flowfields and aerodynamics to flow incidence for flat and cavity tips at different injection locations, in an attempt to explore the potential of further reduction of tip clearance losses at various incidences by non-uniform tip injection concept. First, a linear cascade validation is introduced, and the computations were compared with the experimental data to identify the ability of the computational fluid dynamics (CFD) code to predict the tip leakage flow. Flow patterns over the blade tip without injection (WI) at different incidences were shown, and then the sensitivity of endwall flowfields and aerodynamics to incidence at different injection locations was investigated. Also, the effects of non-uniform tip injection on aerodynamic performance at design and off-design incidences were examined. The results show that the injection in the front part performs better performance than that in the rear part, while it causes turbine performance to be more sensitive to flow incidence than the injection in the rear part. Compared to the flat tip, the coupling effect between cavity tip and tip injection reduces the sensitivity of turbine performance to incidence variation. The non-uniform tip injection, which takes into account the tip leakage flow mechanisms at different incidences, optimizes the mixing process between the tip clearance flow and the passage flow, further improving the design and off-design performance of turbines.

Active control of the tip vortex: an experimental investigation on the performance characteristics of a model turbine

This study is part of an on-going experimental research campaign that focuses on the active control of the tip leakage/vortex characteristics of a model horizontal axis wind turbine rotor using tip injection. This paper presents both baseline (no-injection) data as well as data with tip injection, concentrating on the effects of tip injection on power and thrust variations with the Tip Speed Ratio (TSR). The experiments are conducted by placing a specially designed 3-bladed model wind turbine rotor at the exit of a 1.7 m diameter open-jet wind tunnel. The rotor blades are non-linearly twisted and tapered with NREL S826 airfoil profile all along the span. 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. Baseline results show that the general trends are as expected for a small wind turbine and the maximum power coefficient is reached at around TSR=4.5. Results with injection show that the tip injection has significant effect on the power and thrust coefficients in comparison to the baseline data, especially at TSR values higher than the max CP TSR value. Both coefficients seem to be significantly increased due to tip injection and the max CP TSR value also gets shifted to a slightly higher TSR value. Tip injection seems to have no significant effect for TSR values less than 3.5.

The effect of injector size on compressor performance in a transonic axial compressor with discrete tip injection

The present study investigates the effects of injector size, which covers both circumferential extent and radial extent on compressor stability and radial work redistribution using time-accurate three-dimensional numerical simulations for multi-passages in a transonic compressor with discrete tip injection. Injector width ranges from 1% to 14.5% of casing perimeter and injector throat height varies from 2 to 6 times the height of rotor tip clearance. Six identical injectors are uniformly mounted around the annulus. Results indicate that, with sufficient covering of injection, tip injection can significantly improve compressor stability. Stability margin is improved by 3.5% employing 0.65% of the annulus mass flow. With injector width increased, stability improves sharply when the width is less than 4.5% of casing perimeter, but increases flatly for the rest coverage. Expanding injector throat height to an intermediate level can further enhance compressor stability, but excessive throat height is detrimental on account of the deterioration of the aerodynamic characteristic of Coanda injector. The average decrement of the blockage in injection region, which is defined as injection efficiency, is a key factor that takes primary responsibility for the capacity of tip injection in stability improvement. Injection efficiency derived from the same operating condition for all the configurations with tip injection is well-qualified to estimate the trend of stability improvement. The unsteady influence on radial work redistribution is much more significant than the time-averaged one.

Aero-thermal performance improvements of unshrouded turbines through management of tip leakage and injection flows

The tip leakage flow not only is responsible for a significant amount of aerodynamic losses in a turbine stage, but also leads to high heat-loads on the tip region. The paper presents a numerical investigation of influences of tip injection on aero-thermal performance of the tip leakage flow for both flat tip and cavity tip in an unshrouded turbine rotor, in an attempt to improve the turbine blade tip aero-thermal performance by the management of tip leakage and injection flows. The effects studied include the sensitivities to the geometrical clearance height and the injection mass flow rate. The results show that, at all tip clearances, tip injection has a good effect on the control of the leakage flow, and it significantly reduces the sensitivities of turbine performances to the effects of the tip clearance height. With tip injection, cavity tip geometry does not play a major role in the turbine performance improvement, but it obtains the good film-cooling performance on the blade tip. Tip clearance height, blade tip geometry and injection mass flow rate have related effects on the blade tip aero-thermal performance, and the turbine blade tip obtains the best aero-thermal performance with an optimum injection mass flow rate.

Experimental investigation of aerodynamic interaction between tip leakage flow and spontaneous tip injection flow using 2D-PIV

This paper aims to investigate the flow field characteristics of tip leakage flow in a linear cascade with single-hole spontaneous tip injection (STI) introduced as a passive control mechanism. A small-scale low-speed wind tunnel test rig was developed and the planar flow field adjacent to the injection hole was measured under different operating conditions using 2D-PIV technique. This paper presented the detailed aerodynamic interaction between the STI and the tip leakage flow (TLF) under the both laminar and turbulent flow conditions in the tip clearance. Based on the measurement results, we found that the maximum suppression effect occurred in the 3m/s case in the range of test velocity, and the suppression mechanism of spontaneous tip injection on tip leakage flow were illuminated preliminarily. The vortical structure similar to the Karman vortex street (KVS) appearing in the wake of tip injection flow was noticed and discussed briefly in this paper.

Aerodynamic optimization of a transonic axial compressor with a casing groove combined with tip injection

A multiobjective optimization to enhance the stall margin and peak adiabatic efficiency of an axial compressor with a casing groove combined with injection was performed in this work. The geometry of the casing groove was optimized using a hybrid multiobjective evolutionary algorithm coupled with a surrogate model. Reynolds-averaged Navier–Stokes equations with a k– ɛ turbulence model were discretized by finite volume approximations and solved on hexahedral grids to analyze the flow in the compressor. The stall margin and peak adiabatic efficiency were selected as objective functions with three design variables related to the geometry of the casing groove. Latin hypercube sampling was applied as a design-of-experiment technique to generate 25 design points within the design space. Response surface approximation models as the surrogate models for the objectives were constructed based on the objective function values at the design points. A fast nondominated sorting genetic algorithm for the local search coupled with the surrogate models was applied to determine the global Pareto-optimal solutions. The tradeoff between the two objectives was determined and is described with respect to the Pareto-optimal solutions. The multiobjective optimization results showed that the stall margin and peak adiabatic efficiency of the axial compressor with an optimized casing groove combined with injection were simultaneously improved compared to the compressor with a smooth casing.

Assessment of various rotor tip geometries on a single stage gas turbine performance

Tip leakage loss introduces major part of losses of the rotor in axial gas turbines. Therefore, the rotor blade tip has a considerable effect on rotor efficiency. To understand the flow physics of the rotor tip leakage, we solve the flow field for different tip platforms (passive flow control) and by considering coolant tip injection (active flow control). Various blade tip configurations such as squealers and extensions on both pressure and suction sides, partial PS-squealer and flat tip with various tip clearances are generated. The computational domains are generated using unstructured prism layers for boundary layer resolution and unstructured, tetrahedral mesh for main flow. By using a finite volume CFD solver capable of solving RANS equations in an unstructured domain, the transonic compressible flow in the domain is solved. To capture the turbulent field in blade tip, shear stress transport (SST) k-ω model is employed. By using mixing plane approach, it is possible to couple outlet boundary of stator and inlet boundary of rotor and investigate the stator-rotor interaction in the rotor flow field and its consequence tip leakage flow. To investigate the combined effects of active and passive flow control measures in blade tip region, we simulate baseline geometry with and without tip coolant to show the effects of geometrical features of the rotor tip as well as the effect of tip coolant mass flow rate. Taking into account various rotor tip configurations and their tip leakage losses, it is possible to propose an optimum configuration.

Parametric Study on Aerodynamic Performance of a Transonic Axial Compressor with a Casing Groove and Tip Injection

This paper presents a parametric study on aerodynamic performance of a transonic axial compressor combined with a casing groove and tip injection using three-dimensional Reynolds-average Navier-Stokes equations. The front and rear lengths and height of the groove are selected as the geometric parameters to investigate their effects on the stall margin and peak adiabatic efficiency. These parameters are changed with constant injection. The validation of the numerical results is performed in comparison with experimental data for the total pressure ratio and adiabatic efficiency. As the results of the parametric study, the maximum stall margin and peak adiabatic efficiency are obtained in the axial compressor having 70% groove height of the reference groove. The stall margin and peak adiabatic efficiency in other cases are also improved in comparison with the axial compressors with the smooth casing and reference groove. The results show that both the stall margin and the peak adiabatic efficiency are considerably improved by the application of the casing groove combined with tip injection in an axial compressor.

The Effects of Wet Compression and Blade Tip Water Injection on the Stability of a Transonic Compressor Rotor

The rotor blade tip leakage flow and associated formation of the tip leakage vortex and interaction of the tip leakage vortex with the shockwave, particularly in the case of a transonic compressor rotor have significant impact on the compressor performance and its stability. Air injection upstream of the compressor rotor tip has been shown to improve compressor performance and enhance its stability. The air required for rotor blade tip injection is generally taken from the later stages of the compressor thus causing penalty on the gas turbine performance. In this study, effects of water injection at the rotor tip with and without the wet compression on the compressor performance and its stability have been examined. To achieve the stated objectives, the well tested transonic compressor rotor stage, NASA rotor stage 37, has been numerically simulated. The evaluation of results on various performance parameters, such as total pressure ratio, inlet flow capacity, and adiabatic efficiency combined with contours of total pressure losses, entropy, Mach number, and temperature including limiting streamlines, shows that the blade tip water injection could help in reducing low energy region downstream of the shockwave and strength of the tip leakage vortex with the compressor operating at its rotating stall boundary condition. The extent of reduction depends on the droplet size, injection flow rate, and its velocity. Furthermore, results show that combined case of the blade tip water injection and the wet compression could provide better stall margin enhancement than the blade tip water injection case.

Aerodynamic and Heat Transfer Simulation of Cooling Turbine Blade with Different Tips

This paper studies the aerodynamic and heat transfer influence of tip structures for cooling turbine blade. Four blades with different tip features are discussed, and coupling aerodynamic and heat transfer method is used to accomplish the simulation. The results show that squealer tip can greatly reduce the heat transfer between tip surface and high temperature gas, and also it reduces tip leakage, to some extent. That’s because it exists obviously eddy near the tip surface. Tip injection holes can cool the tip surface effectively, and it will greatly reduce the temperature of tip surface. However, injection holes improve tip leakage slightly.

Effects of tip injection on the performance of a multi-stage high-pressure compressor

Within the European research project NEWAC (New Aero Engine Core Concepts), a multi-stage high-pressure compressor equipped with a tip injection system upstream of the first rotor was tested in three different configurations at MTU Aero Engines. One aim of the test campaign was to investigate the effects of tip injection on the compressor performance. This paper gives an overview of the influences of tip injection on the characteristics of the first three stages. Following an outline of the motivation for tip injection, it is assessed to what extent the surge behavior of the tested compressor is affected by tip injection. The assessment is made by evaluating the surge line extension due to tip injection. If the injection system is applied in an engine, re-matching of its turbo components will occur. Due to this fact, the focus is placed on evaluating the benefits afforded by the use of the injection system in an aircraft engine. The test results are integrated in an existing engine model for a next generation geared turbofan engine and off-design simulations are performed. In this way, changes in surge margin due to tip injection are evaluated. In addition to mere tip injection tests, measurement data of test cases is analyzed, in which mass flow recirculation was simulated. The evaluation of these tests is discussed analogously to the test cases of tip injection. It is found that tip injection prevents the generation of stall cells almost completely. The analyses also show that the stage matching of the multi-stage compressor is changed by tip injection at the front stage. According to the synthesis calculations carried out, recirculation increased the surge margin at part speed by up to about 35% relative to the reference compressor without tip injection.

Influence of Tip Injection and Film Cooling for Blade Tip Flow and Heat Transfer

A numerical based study was conducted to further understanding of turbine tip leakage and flow mechanisms for squealer tip blade. Three blade geometry models with different tips are established. They are squealer tip blade, squealer tip with injection holes blade, squealer tip with injection and film cooling holes blade, separately. Coupled aerodynamic and heat transfer numerical simulation method is used to study blade tip flow and heat transfer based the whole blade computational model. The results show that tip coolant injection will perform a positive effect for the resisting tip leakage, and it will reduce the temperature of blade tip surface and squealer rim, greatly. Film cooling near tip can cool blade squealer rim effectively, but it brings extra total pressure loss.

Injection profile effects on low speed axial compressor stability enhancement

This study presents stability enhancement of a four-stage low speed axial compressor with different injection profiles. The injection profiles include one-step injection, multi-step injection, and continuous injection. For the tip injection, eight Coanda-shaped nozzles have been installed at eight equally spaced circumferential locations upstream of the first stage rotor. Two external blowers injected air steadily through the Coanda-shaped nozzles. With tip injection, the compressor operation range has been extended. To analyze stall margin improvement, spatial Fourier transform (SFT) has been performed. The coefficient of SFT (SFC) is a complex number, containing information about the magnitude and the phase of SFC. By analyzing the distribution of the magnitude and the phase of SFC, the stall onset point has been verified. Furthermore, the injection flow rate has been changed during injection process to examine the possibility of attaining an additional flow extension. Increasing the injection rate during stabilization can bring about additional operation range extension. These results suggest a new injection method to reduce the total amount of the injection air.

Experimental and numerical investigations of tip injection on tip clearance flow in an axial turbine cascade

This investigation presents detailed experimental measurements of an active tip-clearance control method based on tip injection in a high-turning axial turbine cascade. Besides that, numerical investigations are also conducted to study phenomena which are not easily measured in the experiments. It aims to study the influence of tip injection on tip clearance flow, with emphasis on the effects of injection locations. Detailed flow field measurements were made downstream of the cascade using a three-hole probe. Static pressure distributions were also measured on the blade surface at 50% and 97.5% span, respectively. The results suggest that tip injection can weaken tip clearance flow, reducing the tip clearance mass flow and its associated losses. Meanwhile, the heat transfer condition on the blade tip surface can be also improved significantly. It also can be found that injection chordwise location plays an important role in the redistribution of secondary flow within the cascade passage. When the same number of injection holes and injection mass flow are applied, holes located in the aft part of blade can perform much better than that in the front part.

Evaluation of the reaction of early maturing maize genotypes to common smut using artificial inoculation

In order to study of the resistance of early maize genotypes, 44 lines, and hybrids in 2008 and 30 genotypes in 2009 in RCBD were conducted at Karaj and Esfahan Stations. All of the ears were inoculated by tip injection method at suitable time. Inoculation was carried out with syringe (3ml/each ear) at silking stage. Evaluation was done on ears 3-4 weeks after inoculation. The results of variance analysis and mean comparison showed that there is a different reaction among material to disease. In this study, after harvesting of ears, the resistance of each genotype was determined based on disease severity index (0-7). Among examined lines in 2008, line no. (41) (KE 77004/1-1-1) was specified as susceptible and no. (28 and 42) (KE 77003/1-8-1) and (37A) as resistant lines. Also among hybrids, K SC 400 was identified as resistant hybrid. Also, among lines in 2009, line no. (29) (KE77004/1-1-1) was specified as susceptible and line no. (27) (KE77005/4) as resistant line respectively. Among hybrids, hybrid no. (9) (KE77006/3 ?K1263/1) evaluated as resistant hybrid.

0611 翼端噴出しによるタービン動翼端漏れ渦の制御に関する数値的研究(OS6-3 流体機械のCFD解析最前線,オーガナイズドセッション)

0611 翼端噴出しによるタービン動翼端漏れ渦の制御に関する数値的研究(OS6-3 流体機械のCFD解析最前線,オーガナイズドセッション)