Blade Forcing Function and Aerodynamic Work Measurements in a High Speed Centrifugal Compressor With Inlet Distortion

2010 ◽  
Vol 132 (9) ◽  
Author(s):  
Albert Kammerer ◽  
Reza S. Abhari
Keyword(s):  
High Speed ◽  
Pressure Sensors ◽  
Forced Response ◽  
Blade Surface ◽  
Centrifugal Compressors ◽  
Flow Distortion ◽  
Unsteady Pressure ◽  
Inlet Distortion ◽  
Forcing Function ◽  
Work Distribution

Centrifugal compressors operating at varying rotational speeds, such as in helicopters or turbochargers, can experience forced response failure modes. The response of the compressors can be triggered by aerodynamic flow nonuniformities such as with diffuser-impeller interaction or with inlet distortions. The work presented here addresses experimental investigations of forced response in centrifugal compressors with inlet distortions. This research is part of an ongoing effort to develop related experimental techniques and to provide data for validation of computational tools. In this work, measurements of blade surface pressure and aerodynamic work distribution were addressed. A series of pressure sensors were designed and installed on rotating impeller blades and simultaneous measurements with blade-mounted strain gauges were performed under engine representative conditions. To the best knowledge of the authors, this is the first publication, which presents comprehensive experimental unsteady pressure measurements during forced response, for high-speed radial compressors. The experimental data were obtained for both resonance and off-resonance conditions with uniquely tailored inlet distortion. This paper covers aspects relating to the design of fast response pressure sensors and their installation on thin impeller blades. Additionally, sensor properties are outlined with a focus on calibration and measurement uncertainty estimations. The second part of this paper presents unsteady pressure results taken for a number of inlet distortion cases. It will be shown that the intended excitation order due to inlet flow distortion is of comparable magnitude to the second and third harmonics, which are consistently observed in all measurements. Finally, an experimental method will be outlined that enables the measurement of aerodynamic work on the blade surface during resonant crossing. This approach quantifies the energy exchange between the blade and the flow in terms of cyclic work along the blade surface. The phase angle between the unsteady pressure and the blade movement will be shown to determine the direction of energy transfer.

Blade Forcing Function and Aerodynamic Work Measurements in a High Speed Centrifugal Compressor With Inlet Distortion

2009 ◽  
Author(s):  
Albert Kammerer ◽  
Reza S. Abhari
Keyword(s):  
Failure Modes ◽  
Pressure Sensors ◽  
Forced Response ◽  
Blade Surface ◽  
Centrifugal Compressors ◽  
Flow Distortion ◽  
Unsteady Pressure ◽  
Inlet Distortion ◽  
Forcing Function ◽  
Work Distribution

Centrifugal compressors operating at varying rotational speeds, such as in helicopters or turbochargers, can experience forced response failure modes. The response of the compressors can be triggered by aerodynamic flow non-uniformities, such as with diffuser-impeller interaction or with inlet distortions. The work presented here addresses experimental investigations of forced response in centrifugal compressors with inlet distortions. This research is part of an ongoing effort to develop related experimental techniques and to provide data for validation of computational tools. In this work measurements of blade surface pressure and aerodynamic work distribution were addressed. A series of pressure sensors were designed and installed on rotating impeller blades and simultaneous measurements with blade-mounted strain gauges were performed under engine representative conditions. To the best knowledge of the authors, this is the first publication which presents comprehensive experimental unsteady pressure measurements during forced response for highspeed radial compressors. Experimental data were obtained for both resonance and off-resonance conditions with uniquely tailored inlet distortion. This paper covers aspects relating to the design of fast response pressure sensors and their installation on thin impeller blades. Additionally, sensor properties are outlined with a focus on calibration and measurement uncertainty estimations. The second part of this paper presents unsteady pressure results taken for a number of inlet distortion cases. It will be shown that the intended excitation order due to inlet flow distortion is of comparable magnitude to the second and third harmonics which are consistently observed in all measurements. Finally, an experimental method will be outlined that enables the measurement aerodynamic work on the blade surface during resonant crossing. This approach quantifies the energy exchange between the blade and the flow in terms of cyclic work along the blade surface. The phase angle between the unsteady pressure and the blade movement will be shown to determine the direction of energy transfer between the blade and the fluid.

Unsteady Computational Fluid Dynamics Investigation on Inlet Distortion in a Centrifugal Compressor

2010 ◽  
Vol 132 (3) ◽  
Author(s):  
Armin Zemp ◽  
Albert Kammerer ◽  
Reza S. Abhari
Keyword(s):  
Centrifugal Compressor ◽  
Temporal Evolution ◽  
Flow Distribution ◽  
Forced Response ◽  
Inlet Section ◽  
Flow Distortion ◽  
Inlet Flow ◽  
Inlet Distortion ◽  
Forcing Function ◽  
Unsteady Fluid

Blade failure in turbomachinery is frequently caused by an excessive resonant response. Forced response of the blades originates from unsteady fluid structure interactions as conditioned in the inlet section by duct bends, struts, or inlet guide vanes. This paper presents the computational part of a research effort that focuses on the blade forced response in a centrifugal compressor. Unsteady fluid flow simulations are used to quantify the forcing function acting on the compressor blades due to inlet flow distortion. The measured inlet flow distribution is applied as inlet boundary conditions in the computation. The unsteady investigation provided the temporal evolution of the distorted flow through the compressor. The time-resolved blade pressure distribution showed the temporal evolution of the dynamic load on the blade surface caused by the inlet distortion. The results suggest that the forcing function is most sensitive in the leading edge region due to inlet angle variations. Toward the impeller stability line the increase in incidence caused separation on the suction side of the main blade and therefore considerably altered the amplitude and the phase angle of the unsteadiness. The investigation of the effect of idealizing the inlet flow distribution on the forcing function showed an increase in the peak amplitude of approximately 30% compared with the actual inlet flow distribution.

Unsteady CFD Investigation on Inlet Distortion in a Centrifugal Compressor

2008 ◽  
Author(s):  
Armin Zemp ◽  
Albert Kammerer ◽  
Reza S. Abhari
Keyword(s):  
Centrifugal Compressor ◽  
Temporal Evolution ◽  
Flow Distribution ◽  
Forced Response ◽  
Inlet Section ◽  
Flow Distortion ◽  
Inlet Flow ◽  
Inlet Distortion ◽  
Forcing Function ◽  
Unsteady Fluid

Blade failure in turbomachinery is frequently caused by an excessive resonant response. Forced response of the blades originates from unsteady fluid structure interactions as conditioned in the inlet section by duct bends, struts or inlet guide vanes. This paper presents the computational part of a research effort that focuses on the blade forced response in a centrifugal compressor. Unsteady fluid flow simulations are used to quantify the forcing function acting on the compressor blades due to inlet flow distortion. The measured inlet flow distribution is applied as inlet boundary conditions in the computation. The unsteady investigation provided the temporal evolution of the distorted flow through the compressor. The time-resolved blade pressure distribution showed the temporal evolution of the dynamic load on the blade surface caused by the inlet distortion. The results suggest that the forcing function is most sensitive in the leading edge region due to inlet angle variations. Towards the impeller stability line the increase in incidence caused separation on the suction side of the main blade and therefore considerably altered the amplitude and the phase angle of the unsteadiness. The investigation of the effect of idealizing the inlet flow distribution on the forcing function showed an increase of the peak amplitude of approximately 30% compared to the actual inlet flow distribution.

Aerodynamic Excitation and Forced Response of Centrifugal Compressor Impeller in Inlet Distortion

2015 ◽  
Author(s):  
Yixiong Liu ◽  
Dazhong Lao ◽  
Ce Yang ◽  
Leilei Wang ◽  
Du Li
Keyword(s):  
Pressure Fluctuation ◽  
Forced Response ◽  
Centrifugal Impeller ◽  
Aerodynamic Load ◽  
Individual Response ◽  
Blade Surface ◽  
Transient Pressure ◽  
Fe Method ◽  
Inlet Distortion ◽  
Compressor Impeller

The forced response of the turbomachinery blade originates from unsteady fluid structure interactions due to the fluctuating aerodynamic load. As one of the primary unsteady issues, inlet distortion flow breaks the uniformity of airflow through the compressor channel which deteriorates the aerodynamic performance of the compressor and intensifies the pressure fluctuation on the blade surface. The work presented here arms to investigate the forced response of a centrifugal impeller induced by compressor inlet distortion. For this purpose, the unsteady flow computation was carried out to provide the temporal evolution of the distorted flow through the compressor and also to quantify the aerodynamic loads acting on the compressor blade due to inlet distortion flow compared with uniform inlet. Meanwhile, the experimental measurement was performed to obtain the transient pressure fluctuation on the blade surface and to validate the accuracy of numeric calculation. The forced response of the compressor impeller based on unsteady excitation was simulated in a finite element (FE) method to gain insight into vibration characteristic of each blade. Time-resolved blade pressure showed the drastic load fluctuation caused by distorted flow mainly located in the blade leading edge region due to the inlet airflow variation. Towards the impeller forced vibration, each blade shows individual response amplitude due to the phase angle difference among the blades. The effect of inlet distortion on the forced response of impeller increases significantly compared with that of the uniform inlet flow.

Shock Propagation and MPT Noise From a Transonic Rotor in Nonuniform Flow

2012 ◽  
Vol 135 (1) ◽  
Author(s):  
Jeffrey J. Defoe ◽  
Zoltán S. Spakovszky
Keyword(s):  
High Speed ◽  
Acoustic Energy ◽  
Shock Propagation ◽  
Far Field ◽  
Nonuniform Flow ◽  
Mean Flow ◽  
Flow Distortion ◽  
Inlet Distortion ◽  
Circumferential Extent ◽  
Transonic Rotor

One of the major challenges in high-speed fan stages used in compact, embedded propulsion systems is inlet distortion noise. A body-force-based approach for the prediction of multiple-pure-tone (MPT) noise was previously introduced and validated. In this paper, it is employed with the objective of quantifying the effects of nonuniform flow on the generation and propagation of MPT noise. First-of-their-kind back-to-back coupled aero-acoustic computations were carried out using the new approach for conventional and serpentine inlets. Both inlets delivered flow to the same NASA/GE R4 fan rotor at equal corrected mass flow rates. Although the source strength at the fan is increased by 38 dB in sound power level due to the nonuniform inflow, far-field noise for the serpentine inlet duct is increased on average by only 3.1 dBA overall sound pressure level in the forward arc. This is due to the redistribution of acoustic energy to frequencies below 11 times the shaft frequency and the apparent cut-off of tones at higher frequencies including blade-passing tones. The circumferential extent of the inlet swirl distortion at the fan was found to be two blade pitches, or 1/11th of the circumference, suggesting a relationship between the circumferential extent of the inlet distortion and the apparent cut-off frequency perceived in the far field. A first-principles-based model of the generation of shock waves from a transonic rotor in nonuniform flow showed that the effects of nonuniform flow on acoustic wave propagation, which cannot be captured by the simplified model, are more dominant than those of inlet flow distortion on source noise. It demonstrated that nonlinear, coupled aerodynamic and aero-acoustic computations, such as those presented in this paper, are necessary to assess the propagation through nonuniform mean flow. A parametric study of serpentine inlet designs is underway to quantify these propagation effects.

An Integrated Time-Domain Aeroelasticity Model for the Prediction of Fan Forced Response Due to Inlet Distortion

2000 ◽  
Author(s):  
C. Bréard ◽  
M. Vahdati ◽  
A. I. Sayma ◽  
M. Imregun
Keyword(s):  
Aspect Ratio ◽  
Time Domain ◽  
Pressure Fluctuations ◽  
Forced Response ◽  
Element Formulation ◽  
Unsteady Pressure ◽  
Inlet Distortion ◽  
Low Aspect Ratio ◽  
Modal Model ◽  
Transonic Fan

The forced response of a low aspect-ratio transonic fan due to different inlet distortions was predicted using an integrated time-domain aeroelasticity model. A time-accurate, non-linear viscous, unsteady flow representation was coupled to a linear modal model obtained from a standard finite element formulation. The predictions were checked against the results obtained from a previous experimental programme known as “Augmented Damping of Low-aspect-ratio Fans” (ADLARF). Unsteady blade surface pressures, due to inlet distortions created by screens mounted in the intake inlet duct, were measured along a streamline at 85% blade span. Three resonant conditions, namely 1F/3EO, 1T&2F /8EO and 2S/8EO, were considered. Both the amplitude and the phase of the unsteady pressure fluctuations were predicted with and without the blade flexibility. The actual blade displacements and the amount of aerodynamic damping were also computed for the former case. A whole-assembly mesh with about 2,000,000 points was used in some of the computations. Although there were some uncertainties about the aerodynamic boundary conditions, the overall agreement between the experimental and predicted results was found to be reasonably good. The inclusion of the blade motion was shown to have an effect on the unsteady pressure distribution, especially for the 2F/1T case. It was concluded that a full representation of the blade forced response phenomenon should include this feature.

Inlet Distortion Generated Periodic Aerodynamic Rotor Response

1990 ◽  
Vol 112 (2) ◽  
pp. 298-307 ◽  
Author(s):  
S. R. Manwaring ◽  
S. Fleeter
Keyword(s):  
Rotor Blade ◽  
Amplitude Ratio ◽  
Unsteady Aerodynamics ◽  
Mean Flow ◽  
Suction Surface ◽  
Unsteady Pressure ◽  
Pressure Surface ◽  
Inlet Distortion ◽  
Loading Level ◽  
Forcing Function

Fundamental inlet distortion-generated rotor blade row unsteady aerodynamics, including the effects of both the detailed aerodynamic forcing function for the first time and steady loading are experimentally investigated in an extensively instrumented axial-flow research compressor. A two-per-rev forcing function with three gust amplitude ratios is generated. On the rotor blade pressure surface, the unsteady pressure nondimensionalization compresses the magnitude data with mean flow incidence angle. This is not the case on the higher camber suction surface. These pressure surface unsteady data are primarily affected by the steady loading level, whereas the suction surface unsteady data are a function of the steady loading level and distribution as well as the gust amplitude ratio. In addition, a design inlet distortion blade surface unsteady pressure correlation is considered.

The Cumulative Effects of Forcing Function, Damping, and Mistuning on Blade Forced Response in a High Speed Centrifugal Compressor With Inlet Distortion

2010 ◽  
Vol 132 (12) ◽  
Author(s):  
Albert Kammerer ◽  
Reza S. Abhari
Keyword(s):  
Mass Flow ◽  
Centrifugal Compressor ◽  
High Speed ◽  
Excitation Amplitude ◽  
Forced Response ◽  
Response Amplitude ◽  
Resonance Case ◽  
Inlet Flow ◽  
Aerodynamic Damping ◽  
Work Distribution

The vibratory response amplitude of a blade under forced response conditions depends primarily on the aerodynamic excitation amplitude, on damping, and on the effects of mistuning. The work presented here targets to identify the individual contribution of these parameters to the resultant response amplitude depending on the mass flow and the resonance case. For this purpose, measurements were performed of the excitation amplitude, damping, and response amplitude for a high-speed centrifugal compressor. The inlet flow field was intentionally distorted in order to target specific excitation cases of the first main blade mode. For the compressor used, it was found that the overall damping of the first mode could be considered to be constant for any resonance case and mass flow. For this reason, case-to-case variations in the blade-averaged response amplitude were found to depend solely on the aerodynamic excitation amplitude due to inlet flow distortion. Based on an examination of the aerodynamic work distribution during resonance, zones of either excitation or damping work on the blade surface could be successfully identified. This enabled the conclusion to be drawn that energy transfer is a very localized phenomenon and may significantly change as the mass flow is altered, thereby introducing a redistribution of the blade excitation function. The effect of mistuning was shown to alter aerodynamic damping and response amplitude. However, the variation in aerodynamic damping of individual blades was relatively low, thus suggesting that blade-to-blade variation in response amplitude is primarily driven by energy localization in the sense typically experienced with coupled and mistuned structures.

Measurement of Temperature Effects on Cavitation in a Turbopump Inducer

2015 ◽  
Vol 138 (1) ◽  
Author(s):  
Junho Kim ◽  
Seung Jin Song
Keyword(s):  
Water Temperature ◽  
Temperature Effects ◽  
High Speed ◽  
Pressure Sensors ◽  
Thermal Parameter ◽  
Cavitation Number ◽  
High Speed Camera ◽  
Unsteady Pressure ◽  
Cavitation Performance ◽  
Critical Cavitation

Temperature effects on the critical cavitation number and rotating cavitation in a turbopump inducer have been experimentally investigated in water. Static pressures upstream and downstream of the inducer have been measured to determine the cavitation performance, and cavitation instabilities have been detected using unsteady pressure sensors and a high-speed camera. Two kinds of cavitation instabilities have been identified—rotating cavitation and asymmetric attached cavitation. To quantify temperature effects, nondimensional thermal parameter has been adopted. Increasing water temperature, or increasing nondimensional thermal parameter, lowers the critical cavitation number. Increasing nondimensional thermal parameter also shifts the onset of rotating cavitation to a lower cavitation number and reduces the intensity of rotating cavitation. However, for values larger than 0.540 (340 K, 5000 rpm), the critical cavitation number and the rotating cavitation onset cavitation number become independent of the nondimensional thermal parameter. The onset of the head coefficient degradation correlates with the onset of rotating cavitation regardless of temperature.

scholarly journals Rotating Stall Control in a High-Speed Stage With Inlet Distortion: Part I — Radial Distortion

1998 ◽  
Author(s):  
Z. S. Spakovszky ◽  
H. J. Weigl ◽  
J. D. Paduano ◽  
C. M. van Schalkwyk ◽  
K. L. Suder ◽  
...  
Keyword(s):  
Mass Flow ◽  
High Speed ◽  
Transfer Functions ◽  
Axial Flow ◽  
Rotating Stall ◽  
Forced Response ◽  
Single Stage ◽  
Nasa Lewis Research ◽  
Radial Distortion ◽  
Inlet Distortion

This paper presents the first attempt to stabilize rotating stall in a single-stage transonic axial flow compressor with inlet distortion using active feedback control. The experiments were conducted at the NASA Lewis Research Center on a single-stage transonic core compressor inlet stage. An annular array of 12 jet-injectors located upstream of the rotor tip was used for forced response testing and to extend the compressor stable operating range. Results for radial distortion are reported in this paper. First, the effects of radial distortion on the compressor performance and the dynamic behavior were investigated. Control laws were designed using empirical transfer function estimates determined from forced response results. The transfer functions indicated that the compressor dynamics are decoupled with radial inlet distortion, as they are for the case of undistorted inlet flow. Single-input-single-output (SISO) control strategies were therefore used for the radial distortion controller designs. Steady axisymmetric injection of 4% of the compressor mass flow resulted in a reduction in stalling mass flow of 9.7% relative to the case with inlet distortion and no injection. Use of a robust H∞ controller with unsteady non-axisymmetric injection achieved a further reduction in stalling mass flow of 7.5%, resulting in a total reduction of 17.2%.

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