Showing papers on "Axial compressor published in 2015"

Effects of energetic coherent motions on the power and wake of an axial-flow turbine

Abstract: A laboratory experiment examined the effects of energetic coherent motions on the structure of the wake and power fluctuations generated by a model axial-flow hydrokinetic turbine. The model turbine was placed in an open-channel flow and operated under subcritical conditions. The incoming flow was locally perturbed with vertically oriented cylinders of various diameters. An array of three acoustic Doppler velocimeters aligned in the cross-stream direction and a torque transducer were used to collect high-resolution and synchronous measurements of the three-velocity components of the incoming and wake flow as well as the turbine power. A strong scale-to-scale interaction between the large-scale and broadband turbulence shed by the cylinders and the turbine power revealed how the turbulence structure modulates the turbine behavior. In particular, the response of the turbine to the distinctive von Karman-type vortices shed from the cylinders highlighted this phenomenon. The mean and fluctuating characteristics of the turbine wake are shown to be very sensitive to the energetic motions present in the flow. Tip vortices were substantially dampened and the near-field mean wake recovery accelerated in the presence of energetic motions in the flow. Strong coherent motions are shown to be more effective than turbulence levels for triggering the break-up of the spiral structure of the tip-vortices.

Semi-empirical modelling of a variable speed scroll compressor with vapour injection

Abstract: Vapour injection scroll compressors are nowadays gaining attention in vapour compression systems, especially in high temperature lift application, due to the advantages they provide. To date, proposed models of this kind of compressor are mainly deterministic models, requiring a detailed description of compressor geometry and allowing, in turn, minute calculation of the refrigerant state as function of orbiting angle. Semi-empirical models are largely proposed for standard scroll compressors in order to accurately compute compressor performance without the need of the knowledge of compressor geometrical feature. In this paper, a semi-empirical model of a variable speed scroll compressor with vapour injection is introduced and validated over a set of 63 experimental data finding that 89%–98% of calculated suction and injection refrigerant mass flow rates, compressor electrical power and refrigerant temperature at compressor discharge agree within ±5%, ±10% or ±5 K with respect to the experimental values.

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

Abstract: 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 macroinjection, 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.

A propeller model for general forward flight conditions

Abstract: – The purpose of this paper is to develop a physics-based model for UAV propellers that is capable of predicting all aerodynamic forces and moments in any general forward flight condition such as no flow, pure axial flow and pure side flow etc. , – The methodology adopted in this paper is the widely used Blade Element Momentum Theory (BEMT) for propeller model development. The difficulty arising from the variation of induced flow with blade’s angular position is overcome by supplementing the BEMT with the inflow model developed by Pitt and Peters. More so, high angle of attack aerodynamics is embedded in the simulation as it is likely for the blades to stall in general forward flight, for example during extreme aerobatics/maneuvers. , – The validity of the model is demonstrated via comparison with experiments as well as with other existing models. It is found that one of the secondary forces is negligible while the other is one order of magnitude less than the primary static thrust, and as such may be neglected depending on the level of accuracy required. On the other hand, both secondary moments must be considered as they are of similar order of magnitude as the primary static torque. , – The paper does not consider the swirl component of the induced flow under the assumption that it is negligible compared to the axial component. , – This paper fulfills the identified need of a propeller model for general forward flight conditions, and aims to fill this void in the existing literature pertaining to UAVs.

Computational fluid dynamics analysis of the wake behind the MEXICO rotor in axial flow conditions

Abstract: This paper presents a computational investigation of the wake of the MEXICO rotor. The compressible multi-block solver of Liverpool University was employed, using a low-Mach scheme to account for the low-speed flow near the blade and in the wake. In this study, computations at wind speeds of 10, 15 and 24 m s − 1 were performed, and the three components of the velocity were compared against experimental data around the rotor blade up to one and a half rotor diameters downstream. Overall, fair agreement was obtained with the computational fluid dynamics showing good vortex conservation near the blade. Vorticity values revealed discontinuities in the wake at approximately 70%R, where two different aerofoils with different zero-lift angles are blended. The results suggest that all-Mach schemes for compressible computational fluid dynamics methods can deliver good performance and accuracy over all wind speeds for flows around wind turbines, without the need to switch between incompressible and compressible flow methods.

Simulations and measurements of automotive turbocharger compressor whoosh noise

Abstract: Turbocharger noise has become a major concern in downsized automotive engine development. In this paper, the analysis is focused on the whoosh noise produced by the compressor when it is working near surge. A centrifugal compressor has been acoustically characterized on a turbocharger test rig mounted on an anechoic chamber. Three in-duct pressure signals forming a linear array are registered in order to obtain pressure components. In this way, meaningful pressure spectra and sound intensity level (SIL) compressor maps are obtained, showing an increase of SIL in the frequency window corresponding to whoosh noise. Besides, detached eddy simulations (DES) of the centrifugal compressor flow in two operating conditions near surge are performed. Good agreement is found between the experimental measurements and the CFD solutions in terms of predicted pressure spectra. Flow analysis is used to identify patterns responsible for the different features of the pressure spectra. At the simulated conditions, rotating ...

Intercooled cooling air using existing heat exchanger

Abstract: A gas turbine engine comprises a main compressor section having a high pressure compressor with a downstream discharge, and more upstream locations. A turbine section has a high pressure turbine. A tap taps air from at least one of the more upstream locations in the compressor section, passing the tapped air through a heat exchanger and then to a cooling compressor. The cooling compressor compresses air downstream of the heat exchanger, and delivers air into the high pressure turbine. The heat exchanger also receives air to be delivered to an aircraft cabin. An intercooling system for a gas turbine engine is also disclosed.

Fundamentals of Turbomachines

Abstract: 1. Working Principles 2. Basic Components 3. Fans 4. Compressible Fluids 5. Performance Measurement 6. Steam Turbines 7. Dynamic Similitude 8. Pumps 9. Hydraulic Turbines 10. Wind Turbines 11. Power Gas Turbines 12. Thrust Gas Turbines 13. Axial Compressors 14. Radial Compressors 15. Axial and Radial Turbines for Gases References Index

Synergies between suction and blowing for active high-lift flaps

Abstract: The present 2-D CFD study investigates aerodynamic means for improving the power efficiency of an active high-lift system for commercial aircraft. The high-lift configuration consists of a simple-hinged active Coanda flap, a suction slot, and a flexible droop nose device. The power required to implement circulation control is provided by electrically driven compact compressors positioned along the wing behind the wingbox. The compact compressors receive air from the suction slot, which also represents an opportunity to increase the aerodynamic performance of the airfoil. The present work investigates the aerodynamic sensitivities of shape and location of the suction slot in relation to the maximum lift performance of the airfoil. The main purpose of the study is the reduction of the compressor power required to achieve a target lift coefficient. The compressor power requirements can be reduced in two ways: obtaining a high total pressure at the end of the suction duct (compressor inlet) and reducing the momentum needed by the Coanda jet to avoid flow separation from the flap. These two objectives define the guideline of the suction slot design. As a result, a jet momentum reduction of 16 % was achieved for a target lift coefficient of 5 with respect to the same configuration without suction. Furthermore, the study yielded physical insight into the aerodynamic interaction between the two active flow control devices.

Intercooled cooling air with auxiliary compressor control

Abstract: A gas turbine engine comprises a main compressor section having a high pressure compressor with a downstream discharge, and more upstream locations. A turbine section has a high pressure turbine. A tap taps air from at least one of the more upstream locations in the compressor section, passing the tapped air through a heat exchanger and then to a cooling compressor, which compresses air downstream of the heat exchanger, and delivers air into the high pressure turbine. The cooling compressor rotates at a speed proportional to a speed of at least one rotor in the turbine section. The cooling compressor is allowed to rotate at a speed that is not proportional to a speed of the at least one rotor under certain conditions. An intercooling system for a gas turbine engine is also disclosed.

Estimation of loads on a horizontal axis wind turbine operating in yawed flow conditions

Abstract: Stereoscopic particle image velocimetry (SPIV) has been used to characterize the flow around the blade of a yawed horizontal axis wind turbine model. The goal was to assess the possibility of obtaining the 3D velocity field around the blade, the pressure distribution, and the aerodynamic loads being exerted on the blade under unsteady flow conditions. The SPIV equipment was mounted on a traverse system and provided with phase-locked velocity planes perpendicular to the blade axis, scanning the blade from the root to the tip, at three different azimuthal positions, so as to have information of the time variation of the flow. The pressure distribution and the aerodynamic loads on each plane were obtained via 3D formulation. Main differences encountered when measuring loads in yawed flow compared with axial flow have been discussed. Finally, the consistency of the results with similar results obtained computationally with a panel model was assessed. The proposed methodology presents one step further in the application of SPIV to measure forces on a horizontal axis wind turbine, assessing the possibility of estimating the blade loads when the turbine is operating under non-axial flow conditions, with the goal of better simulating real working operating regimes in a wind farm, where the flow is typically not uniform. The proposed methodology could be developed and used to better understand relevant wind energy issues such as dynamic loading and active load control efficiency, in the future. The processed and averaged flow fields from the experimental SPIV data are made available online to the reader. See appendix for description of the files. Copyright © 2014 John Wiley & Sons, Ltd.

Method and apparatus for controlling a compressor of a gas turbine engine

Abstract: A method of operating a gas turbine engine compressor (14, 16). The method comprises: determining an operating point of the compressor (14, 16), and modulating mass flow of environmental control system input air to maintain the operating point of the gas turbine engine compressor (14, 16) within predetermined limits.

Effect of azimuthal flow fluctuations on flow and flame dynamics of axisymmetric swirling flames

Abstract: Recent studies have clearly shown the important role of swirl fluctuations (or, more precisely, fluctuations in axial vorticity) in the response of premixed flames to flow oscillations. An important implication of this mechanism is that the axial location of the swirler plays a key role in the phase between the acoustic flow excitation source and the resulting axial vorticity fluctuation at the flame. Similar to the previously well recognized role of azimuthal vorticity fluctuations, these swirl fluctuations are vortical and convect at the mean flow velocity, unlike the acoustic flow fluctuations. However, there is a fundamental difference between axial and azimuthal vorticity disturbances in terms of the flow oscillations they induce on the flame. Specifically, azimuthal vorticity disturbances excite radial and axial flow disturbances, while axial vorticity oscillations, in general induce both radial and azimuthal flow fluctuations, but in the axisymmetric case, they only directly excite azimuthal flow fluctuations. The axial vorticity fluctuations do, however, indirectly excite axial and radial velocity fluctuations when the axial vortex tube is tilted off-axis, such as at locations of area expansion. This difference is significant because axisymmetric flames are disturbed only by the velocity component normal to it, which stem from axial and radial velocity components only. This implies that axisymmetric mean flames are not directly affected by azimuthal flow fluctuations, since they are tangential to it. Thus, it is the extent to which the axial vorticity is tilted and rotated that controls the strength of the flow oscillations normal to the flame and, in turn, lead to heat release oscillations. This coupling process is not easily amenable to analytical calculations and, as such, we report here a computational study of the role of these different flow fluctuations on the flame response in an axisymmetric framework. The results indicate that the swirl fluctuations can act as significant source of flame heat release disturbances, due to azimuthal and radial vortex tubes tilting in mixing passage boundary layers and at the expansion into the combustor.