A New Technique for Stabilizing the Flow and Improving the Performance of Vaneless Radial Diffusers

1987 ◽  
Vol 109 (1) ◽  
pp. 36-40 ◽  
Author(s):  
A. N. Abdel-Hamid
Keyword(s):  
Flow Instability ◽  
Pressure Rise ◽  
Outer Radius ◽  
Operating Conditions ◽  
Flow Angle ◽  
Diffuser Flow ◽  
Flow Oscillations ◽  
Inlet Conditions ◽  
A New Technique ◽  
Unsteady Characteristics

Experiments were conducted to investigate the effects of using small exit vanes on the characteristics of an otherwise vaneless radial diffuser of outer radius and width-to-inlet radius ratios of 1.75 and 0.116, respectively. The steady and unsteady characteristics of the diffuser were evaluated as the angle of the vanes was varied continuously at several diffuser inlet conditions. The measurements showed that the influence of the adjustable exit vanes on the diffuser flow field increased as the diffuser inlet flow angle was decreased. Elimination of the self-excited flow oscillations in the diffuser was possible for all operating conditions by appropriate setting of the exit vane angle. Moreover for the diffuser investigated here and with optimum setting of the exit vanes angle the static pressure rise coefficient was significantly improved compared to the case of a pure vaneless diffuser and was found to remain almost constant at low values of diffuser inlet angles. Relative to other techniques for controlling flow instability in vaneless diffusers the proposed method offers mechanical simplicity and improved overall performance.

Flow Instability at the Inlet of a Centrifugal Compressor

1981 ◽  
Vol 103 (2) ◽  
pp. 451-456
Author(s):  
G. Flueckiger ◽  
A. Melling
Keyword(s):  
Centrifugal Compressor ◽  
Flow Instability ◽  
Laser Doppler Anemometry ◽  
Suction Side ◽  
Operating Conditions ◽  
Gas Velocity ◽  
Unstable Flow ◽  
Flow Angle ◽  
Compressor Impeller ◽  
Service Conditions

Using laser Doppler anemometry, two components of the gas velocity have been measured at the inlet of a centrifugal compressor impeller, operated at speeds typical of service conditions for a medium-sized turbocharger. The flow was found to be unstable, especially adjacent to the suction side of the blades, such that two predominant conditions existed in the flow. The unstable flow is illustrated in the paper by distributions of relative velocity and relative flow angle, and the effects of different operating conditions on these distributions are examined. The instability is believed to be caused by a pre-stall condition as the compressor operating point approaches a fully stalled condition which occurs during surge.

Effects of Vaneiess Diffuser Geometry on Flow Instability in Centrifugal Compression Systems

1981 ◽  
Author(s):  
A. N. Abdelhamid
Keyword(s):  
Critical Angle ◽  
Previous Investigation ◽  
System Analysis ◽  
Flow Instability ◽  
Rate Of Change ◽  
Radius Ratio ◽  
Vaneless Diffuser ◽  
Flow Angle ◽  
Flow Oscillations ◽  
Initial Pattern

Experiments were conducted to determine the effects of vaneless diffuser radius ratio on the occurrence of self-excited flow oscillations in a centrifugal compression system. Analysis of the results indicated the successive occurrence of two types of diffuser rotating pressure patterns as the flow rate in the system was gradually decreased. The rotational speed of the latter pattern was higher than that of the initial pattern and both speeds varied inversely with diffuser radius ratio. The critical flow angle at which each pattern was first observed increased with diffuser radius ratio. However, for diffuser radius ratio equal to and larger than 1.75 the rate of change of the critical angle with radius ratio decreased significantly. The results also showed that the minimum diffuser radius ratio necessary for self excitation of each pattern were different. Occurrence of two rotating pressure patterns confirms analytical results presented in a previous investigation.

A three-dimensional vaneless diffuser stall model

2010 ◽  
Vol 224 (9) ◽  
pp. 1933-1945 ◽  
Author(s):  
F Shen ◽  
H Chen ◽  
X-C Zhu
Keyword(s):  
Flow Instability ◽  
Three Dimensional ◽  
Axial Direction ◽  
Wave Number ◽  
Viscous Effects ◽  
Flow Angle ◽  
Linearized Euler Equations ◽  
Diffuser Flow ◽  
Value Decomposition ◽  
The Waves

A three-dimensional (3D) model is presented to study the occurrence of weak rotating waves in vaneless diffusers of centrifugal compressors. The model is an extension of the 2D one developed by Moore. 3D incompressible linearized Euler equations are cast on a rotating frame of reference travelling at the same circumferential speeds as the waves and the viscous effects are ignored. The diffuser is assumed to have two parallel walls and discharge into a large plenum. Solutions to the equations are obtained by a finite difference method and the singular value decomposition technique. Disturbances along the axial direction are found under zero undisturbed axial velocity. Resonant disturbances in the diffuser flow regardless of the compressor characteristics are also found as in the 2D cases found by Moore. Computational results show that both the critical flow angle and the propagation velocity of the wave are affected by the departure from the axial uniform distribution of the undisturbed radial velocity at the diffuser inlet, but the angle is less affected than the wave speed. The velocity distribution that satisfies Fj0rtoft's necessary conditions for flow instability is found slightly less stable and is more affected by the departure than those that do not. Shorter diffusers are affected more by the departure than the longer ones. The critical angle is shown to be increased non-linearly with the wave number and this helps to explain why wave numbers 2 to 4 are commonly observed in experiments. Finally, comparison with the experimental results in the open literature is made and a good agreement is shown.

The Design of an Axial Flow Fan for Application in Large Air-Cooled Heat Exchangers

2012 ◽  
Author(s):  
Francois G. Louw ◽  
Phillipe R. P. Bruneau ◽  
Theodor W. von Backström ◽  
Sybrand J. van der Spuy
Keyword(s):  
Heat Exchangers ◽  
Flow Direction ◽  
Pressure Fluctuations ◽  
Axial Flow ◽  
Pressure Rise ◽  
Volumetric Flow Rate ◽  
Cooling Capacity ◽  
Operating Conditions ◽  
Operating Efficiency ◽  
Inlet Conditions

The heat transfer characteristics of industrial air-cooled heat exchangers (ACHEs) are dependent on the ability of the fan system to deliver sufficient cooling air. However, under normal operating conditions, variable flow direction and strength often subject peripheral fans to distorted inlet conditions with an attendant reduction in overall volumetric flow rate and cooling capacity. In this paper, a design methodology for single-rotor axial flow fans, appropriate for use in large industrial ACHE’s is presented. The primary motivation for this work was to address the issues of robust off-design performance, in particular, distorted inlet flow tolerance. Using this methodology, two 8-bladed prototype fans (B1 and B2) were designed, built and tested in accordance with BS 848 (Type A) standards. The two B-fans have a hub-tip ratio of xh = 0.4 and employ the Clark Y and NASA LS airfoil profiles respectively. Measured performance characteristics were compared to commercial fan designs (V-, DL- and L-fan) used in existing ACHEs. Results indicate that the B-fans have a higher design point operating efficiency. The B-fans also show a steeper fan static pressure rise characteristic compared to the commercial fans, except for the DL-fan, implying a greater tolerance to pressure fluctuations caused by distorted inflows.

Methods for and Benefits of Centrifugal Compressor Design Audits

2003 ◽  
Author(s):  
Robert J. McKee ◽  
Justin R. Hollingsworth ◽  
Anthony J. Smalley
Keyword(s):  
Torsional Vibration ◽  
High Speed ◽  
Performance Test ◽  
Equations Of State ◽  
Pressure Rise ◽  
Rotating Stall ◽  
Operating Conditions ◽  
Design Stage ◽  
Flow Angle ◽  
Process Gas

As gas pipeline and industrial compressors become more powerful and more complex, it has become beneficial to conduct technical audits of these machines in the design stage. Detailed analysis of critical or advanced compressors by independent evaluators have identified operating limitations, resonant responses, potential vibrations, weak components, the onset of stall, and other instabilities, and have recommended ways to eliminate a variety of potential problems before the compressor is placed in operation. The suitability of a compressor and its driver for the planned service should be thoroughly evaluated, so that each component and the system not only satisfy the design conditions, but also extreme operating conditions. This paper presents a description of the tools available for design audits and gives examples of benefits that have resulted from recent audits. The rotordynamics of any large high-speed compressor should be carefully evaluated to identify potential instabilities, high vibration levels, and even destructive responses of the machine. Powerful rotordynamic analysis tools and specific knowledge exists to accurately predict bearing and seal stiffness and damping, lateral critical speeds, and damped forced responses. Some examples of significant results obtained from rotordynamic evaluations are presented, and typical problems that have been identified and eliminated are highlighted. Torsional vibration analyses for compressor trains are an essential aspect of a design audit that have identified vibration problems and weak components. Examples of torsional vibration responses and problems that can be identified and corrected are included in this paper. The aerodynamics of a compressor is a design audit topic to which attention should be paid. Thermophysical properties of the process gas, as it is compressed, are important quantities which can be accurately determined by modern equations of state. The internal velocity distribution and pressure rise per impeller and diffuser can be evaluated to identify areas of excess loss, poor work transfer, or restrictions within a compressor. Flow angles such as at the impeller and diffuser entrances can be predicted and evaluated. The diffuser inlet flow angle is a critical indicator of the onset of rotating stall. This type of aerodynamic analysis also provides important input for performance test planning and evaluation. This paper concludes with a summary of benefits of design audits for pipeline and industrial compressors.

Surge in a Low-Speed Radial Compressor

1998 ◽  
Author(s):  
Corine Meuleman ◽  
Frank Willems ◽  
Rick de Lange ◽  
Bram de Jager
Keyword(s):  
Flow Rate ◽  
Pressure Rise ◽  
Flow Coefficient ◽  
Lumped Parameter Model ◽  
Pressure Oscillations ◽  
Vaned Diffuser ◽  
Flow Angle ◽  
Radial Compressor ◽  
Low Speed ◽  
Lumped Parameter

Surge is measured in a low-speed radial compressor with a vaned diffuser. For this system, the flow coefficient at surge is determined. This coefficient is a measure for the inducer inlet flow angle and is found to increase with increasing rotational speed. Moreover, the frequency and amplitude of the pressure oscillations during fully-developed surge are compared with results obtained with the Greitzer lumped parameter model. The measured surge frequency increases when the compressor mass flow is throttled to a smaller flow rate. Simulations show that the Greitzer model describes this relation reasonably well except for low rotational speeds. The predicted amplitude of the pressure rise oscillations is approximately two times too small when deep surge is met in the simulations. For classic surge, the agreement is worse. The amplitude is found to depend strongly on the shape of the compressor and throttle characteristic, which are not accurately known.

Improved Diffuser/Volute Combinations for Centrifugal Compressors

2008 ◽  
Vol 130 (1) ◽  
Author(s):  
T. Steglich ◽  
J. Kitzinger ◽  
J. R. Seume ◽  
R. A. Van den Braembussche ◽  
J. Prinsier
Keyword(s):  
Cross Sections ◽  
Pressure Ratio ◽  
Pressure Rise ◽  
Outer Radius ◽  
Inner Radius ◽  
Pressure Pipeline ◽  
The Cross ◽  
Improved Performance ◽  
High Pressure Pipeline ◽  
Original Configuration

Internal volutes have a constant outer radius, slightly larger than the diffuser exit radius, and the circumferential increase of the cross section is accommodated by a decrease of the inner radius. They allow the design of compact radial compressors and hence are very attractive for turbochargers and high-pressure pipeline compressors, where small housing diameters have a favorable impact on weight and cost. Internal volutes, however, have higher losses and lower pressure rise than external ones, in which the center of the cross sections is located at a larger radius than the diffuser exit. This paper focuses on the improvement of the internal volute performance by taking into account the interaction between the diffuser and the volute. Two alternative configurations with enhanced aerodynamic performance are presented. The first one features a novel, nonaxisymmetric diffuser̸internal volute combination. It demonstrates an increased pressure ratio and lower loss over most of the operating range at all rotational speeds compared with a symmetric diffuser̸internal volute combination. The circumferential pressure distortion at off design operation is slightly larger than in the original configuration with a concentric vaneless diffuser. Alternatively, a parallel-walled diffuser with low-solidity vanes and an internal volute allows a reduction of the unsteady load on the impeller and an improved performance, approaching that of a vaneless concentric diffuser with a large external volute.

Feasibility of High Speed Furnace Drawing of Optical Fibers

2004 ◽  
Vol 126 (5) ◽  
pp. 852-857 ◽  
Author(s):  
Xu Cheng ◽  
Yogesh Jaluria
Keyword(s):  
Optical Fibers ◽  
High Speed ◽  
Flow Instability ◽  
Fiber Quality ◽  
Domain Boundary ◽  
Operating Conditions ◽  
Furnace Temperature ◽  
Fiber Drawing ◽  
Heated Zone ◽  
Additional Information

The domain of operating conditions, in which the optical fiber-drawing process is successful, is an important consideration. Such a domain is mainly determined by the stresses acting on the fiber and by the stability of the process. This paper considers an electrical resistance furnace for fiber drawing and examines conditions for process feasibility. In actual practice, it is known that only certain ranges of furnace temperature and draw speed lead to successful fiber drawing. The results obtained here show that the length of the heated zone and the furnace temperature distribution are other important parameters that can be varied to obtain a feasible process. Physical behavior close to the boundary of the feasible domain is also studied. It is found that the iterative scheme for neck-down profile determination diverges rapidly when the draw temperature is lower than that at the acceptable domain boundary due to the lack of material flow. However, the divergence rate becomes much smaller as the temperature is brought close to the domain boundary. Additional information on the profile determination as one approaches the acceptable region is obtained. It is found that it is computationally expensive and time-consuming to locate the exact boundary of the feasible drawing domain. From the results obtained, along with practical considerations of material rupture, defect concentration, and flow instability, an optimum design of a fiber-drawing system can be obtained for the best fiber quality.

Assessment of the Loss Map of a Centrifugal Compressor’s External Volute

2020 ◽  
Author(s):  
Thomas Ceyrowsky ◽  
Andre Hildebrandt ◽  
Martin Heinrich ◽  
Rüdiger Schwarze
Keyword(s):  
Mach Number ◽  
Flow Rate ◽  
Numerical Approach ◽  
Operating Conditions ◽  
Circumferential Velocity ◽  
Flow Angle ◽  
Absolute Flow ◽  
Highly Sensitive ◽  
Geometrical Features ◽  
Comparison With Experimental Data

Abstract A volute’s loss coefficient is highly sensitive to Mach number, circumferential velocity and flow rate at volute inlet. In case of a backswept impeller, these parameters are coupled to each other. An increased flowrate leads to a steeper absolute flow angle at impeller exit and hence to a decrease of circumferential velocity. The absolute Mach number is also altered. Therefore, in order to investigate the effects of flowrate and flow angle separately, one would have to vary the diffuser width together with the flowrate, keeping the flow angle constant. This corresponds to coupling the volute with aerodynamically similar impellers, designed for higher and lower flowrates. Since this is elaborate, there is no adequate study available in open literature, assessing a volute’s global loss map. In this work, a new numerical approach for the prediction of a volute’s representative loss map is presented: The volute is calculated by means of steady CFD as a standalone component. The inlet boundary conditions are carefully selected by means of 1D and applied together with different diffuser widths. This allows for separate investigation of the impacts of flow angle, flow rate and Mach number. Validation against full stage CFD confirms the applicability of the standalone model. The results exhibit that minimum losses do not necessarily occur at the theoretical matching point but either when the volute is smaller or bigger, depending on the inlet flow angle. Investigations of the loss mechanisms at different operating conditions provide useful guidelines for volute design. Finally, the validity of these study’s findings for volutes with different geometrical features is examined by comparison with experimental data as well as with fullstage CFD.

Ethers and esters as alternative fuels for internal combustion engine: A review

2021 ◽  
pp. 146808742110464
Author(s):  
Yang Hua
Keyword(s):  
Alternative Fuels ◽  
Combustion Engine ◽  
Combustion Process ◽  
Pressure Rise ◽  
Engine Performance ◽  
Internal Combustion ◽  
Operating Conditions ◽  
Future Research ◽  
Particulate Emissions ◽  
Ic Engine

Ether and ester fuels can work in the existing internal combustion (IC) engine with some important advantages. This work comprehensively reviews and summarizes the literatures on ether fuels represented by DME, DEE, DBE, DGM, and DMM, and ester fuels represented by DMC and biodiesel from three aspects of properties, production and engine application, so as to prove their feasibility and prospects as alternative fuels for compression ignition (CI) and spark ignition (SI) engines. These studies cover the effects of ether and ester fuels applied in the form of single fuel, mixed fuel, dual-fuel, and multi-fuel on engine performance, combustion and emission characteristics. The evaluation indexes mainly include torque, power, BTE, BSFC, ignition delay, heat release rate, pressure rise rate, combustion duration, exhaust gas temperature, CO, HC, NOx, PM, and smoke. The results show that ethers and esters have varying degrees of impact on engine performance, combustion and emissions. They can basically improve the thermal efficiency of the engine and reduce particulate emissions, but their effects on power, fuel consumption, combustion process, and CO, HC, and NOx emissions are uncertain, which is due to the coupling of operating conditions, fuel molecular structure, in-cylinder environment and application methods. By changing the injection strategy, adjusting the EGR rate, adopting a new combustion mode, adding improvers or synergizing multiple fuels, adverse effects can be avoided and the benefits of oxygenated fuel can be maximized. Finally, some challenges faced by alternative fuels and future research directions are analyzed.

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