Measurements of the Pressure and Velocity Distribution in Low-Speed Turbomachinery by Means of High-Frequency Pressure Transducers

1992 ◽  
Vol 114 (1) ◽  
pp. 100-107 ◽  
Author(s):  
S. Brodersen ◽  
D. Wulff
Keyword(s):  
High Frequency ◽  
Pressure Fluctuations ◽  
Design Flow ◽  
Measuring Technique ◽  
Pressure Probe ◽  
Blade Loading ◽  
Low Speed ◽  
Pressure Transducers ◽  
Multiple Samples ◽  
Very High

The flow in a low-speed, single-state compressor with a very high blade loading has been measured using a two-probe arrangement. The measuring technique and data reduction procedure described have been especially adjusted for application in low-speed turbomachinery. Those machines show only small pressure fluctuations in the flow downstream of the rotor, for which specific requirements concerning the measuring technique have been taken into account. The probes used contain unsteady pressure transducers and simulate an unsteady multisensor pressure probe. This technique proves to be suitable for applications in low-speed turbomachinery. The measurements are based on phase-locked ensemble averages of multiple samples, where the data are acquired using a simple and convenient experimental setup. This allows the velocity and pressure distribution of the flow to be determined in rotor coordinates. The results show the flow field and the loss distribution of an aero-dynamically highly loaded rotor at design flow rate.

Effects of inlet radial distortion on the type of stall precursor in low-speed axial compressor

2016 ◽  
Vol 232 (1) ◽  
pp. 55-67 ◽  
Author(s):  
Ali Arshad ◽  
Qiushi Li ◽  
Simin Li ◽  
Tianyu Pan
Keyword(s):  
Pressure Fluctuations ◽  
Axial Compressor ◽  
Rotating Stall ◽  
Experimental Investigations ◽  
Inlet Flow ◽  
Blade Loading ◽  
Stall Inception ◽  
Low Speed ◽  
Modal Type ◽  
Stall Precursor

Experimental investigations of the effect of inlet blade loading on the rotating stall inception process are carried out on a single-stage low-speed axial compressor. Temporal pressure signals from the six high response pressure transducers are used for the analysis. Pressure variations at the hub are especially recorded during the stall inception process. Inlet blade loading is altered by installing metallic meshed distortion screens at the rotor upstream. Three sets of experiments are performed for the comparison of results, i.e. uniform inlet flow, tip, and hub distortions, respectively. Regardless of the type of distortion introduced to the inflow, the compressor undergoes a performance drop, which is more severe in the hub distortion case. Under the uniform inlet flow condition, stall inception is caused by the modal type disturbance while the stall precursor switched to spike type due to the highly loaded blade tip. In the presence of high blade loading at the hub, spike disappeared and the compressor once again witnessed a modal type disturbance. Hub pressure fluctuations are observed throughout the process when the stall is caused by a modal wave while no disturbance is noticed at the hub in spike type stall inception. It is believed that the hub flow separation contributes to the modal type of stall inception phenomenon. Results are also supported by the recently developed signal processing techniques for the stall inception study.

Pressure Fluctuation of the Low Specific Speed Centrifugal Pump

2012 ◽  
Vol 152-154 ◽  
pp. 935-939 ◽  
Author(s):  
Qiang Fu ◽  
Shou Qi Yuan ◽  
Rong Sheng Zhu
Keyword(s):  
Centrifugal Pump ◽  
Flow Rate ◽  
Pressure Fluctuation ◽  
High Frequency ◽  
Pressure Fluctuations ◽  
Radial Force ◽  
Design Flow ◽  
Rate Condition ◽  
Low Specific Speed ◽  
Specific Speed

In order to study the rules of pressure fluctuation and the radial force under different positions in a centrifugal pump with low specific speed, and to find the relationship between each other, the three-dimensional ,unsteady Reynolds-averaged Navier-stokes equations with shear stress transport turbulent models were solved. The pressure fluctuation was obtained. The results showed that the pressure fluctuations were visible. The pressure fluctuations in the volute were relatively low at the design flow rate condition. The blade passing frequency dominates the pressure fluctuations, high frequency contents were found on the outlet of impeller but no high frequency information occured in casing. The radial force on the impeller was unsteady especially at the small flow rate.

Experimental Investigation of Blade Loading Effects at Design Flow in Rotating Passages of Centrifugal Impellers

1999 ◽  
Vol 121 (4) ◽  
pp. 813-823 ◽  
Author(s):  
Nicholas H. Hesse ◽  
J. H. G. Howard
Keyword(s):  
Boundary Layer ◽  
Relative Velocity ◽  
Laser Doppler Anemometry ◽  
Suction Side ◽  
Design Flow ◽  
Pump Impeller ◽  
Blade Loading ◽  
Loading Effects ◽  
Very High ◽  
Centrifugal Pump Impeller

Laser-Doppler Anemometry (LDA) was used to study the effect of blade loading on the relative velocity field in a rotating passage of a centrifugal-pump impeller. Two variations of the impeller, 8-bladed and 16-bladed, were investigated. The measured primary and secondary velocities and turbulence show that the effect of blade loading is not that previously predicted. The 16-blade impeller with high blade loading has a rapidly thickening suction side boundary layer, suggesting the onset of transient separation near the exit. However, for the 8-blade impeller with even higher blade loading, the onset of separation is not indicated at any measured location in the impeller. At the design flow, it is concluded that the stronger potential eddy and lower solidity associated with the very high blade loading caused a change in the secondary flow pattern, retarding the growth and the likelihood of transitory separation of the suction side boundary layer.

scholarly journals Comprehensive Numerical Investigations of Unsteady Internal Flows and Cavitation Characteristics in Double-Suction Centrifugal Pump

2017 ◽  
Vol 2017 ◽  
pp. 1-13 ◽  
Author(s):  
Xuelin Tang ◽  
Mingde Zou ◽  
Fujun Wang ◽  
Xiaoqin Li ◽  
Xiaoyan Shi
Keyword(s):  
Centrifugal Pump ◽  
Flow Rate ◽  
Pressure Fluctuations ◽  
Dominant Frequency ◽  
Secondary Flows ◽  
Design Flow ◽  
Sharp Drop ◽  
Blade Loading ◽  
Blade Passing Frequency ◽  
Design Flow Rate

The RNG k-ε turbulence model combined with cavitation model was used to simulate unsteady cavitating flows inside a double-suction centrifugal pump under different flow rate conditions based on hexahedral structured grid. The numerical external characteristic performances agree well with the experimental performances. The predicted results show that the turbulence kinetic energy and the turbulence dissipation rate inside the impeller at design flow rate are lower than those at other off-design flow rates, which are caused by various vortexes. Based on frequency-domain analyses in the volute casing, the blade passing frequency is the dominant one of the pressure fluctuations except the vicinity of volute tongue for all operating cases, and the dominant frequency near the volute tongue ranges from 0 to 0.5 times the blade passing frequency for other off-design points, while the blade passing one near the volute tongue is the dominant one of the pressure fluctuations at design point. The increase of flow rate reduces the pressure fluctuations amplitude. For cavitation cases, the blade loading of the middle streamline increases a bit during the initial stage, but, for serious cavitation, the blade loading near the blade inlet reduces to 0 and even negative values, and the serious cavitation bubbles block the blade channels, which results in a sharp drop in pump head. Under noncavitation condition, the predicted power related to the pressure in the impeller channels increases from the inlet to the exit, while, under different cavitation conditions at the design flow rate, these power-transformation distributions in the impeller channels show that these power conversions are affected by the available NPSHa and the corresponding work in leading regions of the blades increases increases gradually a bit, and then it increases sharply in the middle regions, but it decreases in the blade trailing regions and is greatly influenced by secondary flows.

Mitigation of Pressure Fluctuations From an Array of Pulse Detonation Combustors

2021 ◽  
Author(s):  
Mohammad Rezay Haghdoost ◽  
Bhavraj S. Thethy ◽  
Daniel Edgington-Mitchell ◽  
Fabian Habicht ◽  
Johann Vinkeloe ◽  
...  
Keyword(s):  
High Frequency ◽  
Pressure Fluctuations ◽  
Shock Interaction ◽  
Pressure Measurements ◽  
Test Rig ◽  
Velocity Fluctuations ◽  
Firing Patterns ◽  
Pressure Transducers ◽  
Pulse Detonation ◽  
Shock Dynamics

Abstract An annular plenum is integrated downstream of six pulse detonation combustors arranged in a can-annular configuration. The primary purpose of the plenum is the mitigation of pressure and velocity fluctuations, which is crucial for operation with a downstream turbine. The flow inside the plenum is investigated by means of flush-mounted pressure transducers arranged in axial and circumferential directions. The test rig is operated in different firing patterns at frequencies up to 16.7 Hz per tube. Two firing patterns are studied to characterize the shock dynamics inside the plenum. The obtained data allow for a better understanding of shock interaction and attenuation inside the plenum as well as the quantification of pressure fluctuations at the plenum outlet. Furthermore, a comparison is made between piezoresistive and piezoelectric pressure transducers showing the capability of piezoresistive transducers for high frequency pressure measurements.

High-Frequency Acoustic Mode Identification of Unstable Combustors

2019 ◽  
Author(s):  
J. Kim ◽  
T. Lieuwen ◽  
B. Emerson ◽  
V. Acharya ◽  
D. Wu ◽  
...  
Keyword(s):  
High Frequency ◽  
Least Squares Method ◽  
Pressure Fluctuations ◽  
Acoustic Mode ◽  
Modal Identification ◽  
Mode Shapes ◽  
Similar Frequency ◽  
Pressure Transducers ◽  
Mode Identification ◽  
The Time Domain

Abstract High frequency thermoacoustic instabilities are becoming increasingly problematic in modern combustion systems. Understanding which acoustic mode is being excited is important for understanding potential mechanisms and control approaches — for example, influence of a helical shear layer mode on the flame has profoundly different effects on the first tangential acoustic mode, than a higher order axial mode of similar frequency. Nonetheless, the modal density increases with frequency and it becomes increasingly difficult to determine which acoustic mode is self-excited, based upon frequency calculations alone. Moreover, access issues and cost usually limit the number of pressure probes that can be distributed axially and azimuthally in the combustor. This paper presents a methodology for identifying the acoustic mode by using high temperature pressure transducers flush mounted in a combustion chamber. Modal identification is demonstrated with a siren under non-reacting conditions. The siren is mounted on the chamber to excite longitudinal and azimuthal waves. Five acoustic sensors at different axial and azimuthal locations measure the pressure fluctuations simultaneously. Given the forcing frequency and the speed of sound, the pressure distribution in the combustor is reconstructed in the time domain from the measured data by using a least squares method to determine its mode shapes. In addition, the finite element method (FEM) solver is used to provide the eigenfrequencies and corresponding mode shapes. The test results demonstrate that the mode shapes from the reconstructed data and corresponding frequencies are consistent with those predicted from the FEM, which validates the methodology in this study. In addition, the methodology is extended to practical reacting cases without the siren to determine the acoustic mode shapes of naturally occurring instabilities. In these cases, the modal features have strong stochastic features, such as what appear to be stochastic variations in overall amplitude and relative amplitudes of clockwise and counterclockwise waves.

Experimental Investigation of very High Frequency Slot Antenna on M-60A-1 Tank

1977 ◽  
Author(s):  
D. V. Campbell ◽  
William Kennebeck ◽  
A. Zanella ◽  
Paul Sexton
Keyword(s):  
Experimental Investigation ◽  
High Frequency ◽  
Slot Antenna ◽  
Very High Frequency ◽  
Very High

A collision feedback based multiple access control protocol for very high frequency data exchange system in E-navigation

2021 ◽  
pp. 1-16
Author(s):  
Xu Hu ◽  
Bin Lin ◽  
Ping Wang ◽  
Hongguang Lyu ◽  
Tie-Shan Li
Keyword(s):  
Access Control ◽  
High Frequency ◽  
Multiple Access ◽  
Data Exchange ◽  
High Frequency Data ◽  
Frequency Data ◽  
Exchange System ◽  
Very High Frequency ◽  
Time Division ◽  
Very High

Abstract The very high frequency data exchange system (VDES) is promising in promoting electronic navigation (E-navigation) and improving navigation safety. The multiple access control (MAC) protocol is crucial to the transmission performance of VDES. The self-organising time division multiple access (SOTDMA) protocol, as the only access mode given by current recommendations, leads to a high rate of transmission collisions in the traditional automatic identification system (AIS), especially with heavy traffic loads. This paper proposes a novel feedback based time division multiple access (FBTDMA) protocol to address the problems caused by SOTDMA, such that collision of transmissions can be avoided in information transmission among vessels. Simulation results demonstrate that the proposed FBTDMA outperforms the traditional SOTDMA in terms of channel utilisation and throughput, and significantly reduces the transmission collision rate. The study is expected to provide insights into VDES standardisation and E-navigation modernisation.

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