Estimating Inducer Blade Damping in Water with On-Blade Strain Measurements

This paper describes the testing, methodology, and results for estimating critical damping ratios of inducer blade structural natural frequencies. A sub-scale inducer water flow test was performed with on-blade strain gauge measurements. Data were acquired in quiescent air and water, and also at several shaft speeds and operating conditions. Two methods were used to provide active excitation to the blades. The first was to impart a mechanical impulse to the inducer shaft and observe the strain gauge response. The second was to install a stator plate upstream of the inducer to create a non-uniform but regular pressure field at the inducer inlet. There are challenges with using either approach, but damping information was extracted using both methods. Results showed that the critical damping ratio for a given blade mode increased from air to quiescent water, and also increased when the inducer was spinning

Synthetic chemical inducers and genetic decoupling enable orthogonal control of the rhaBAD promoter

External control of gene expression is crucial in synthetic biology and biotechnology research and applications, and is commonly achieved using inducible promoter systems. The E. coli rhamnose-inducible rhaBAD promoter has properties superior to more commonly-used inducible expression systems, but is marred by transient expression caused by degradation of the native inducer, L-rhamnose. To address this problem, 35 analogs of L-rhamnose were screened for induction of the rhaBAD promoter, but no strong inducers were identified. In the native configuration, an inducer must bind and activate two transcriptional activators, RhaR and RhaS. Therefore, the expression system was reconfigured to decouple the rhaBAD promoter from the native rhaSR regulatory cascade so that candidate inducers need only activate the terminal transcription factor RhaS. Re-screening the 35 compounds using the modified rhaBAD expression system revealed several promising inducers. These were characterised further to determine the strength, kinetics and concentration-dependence of induction; whether the inducer was used as a carbon source by E. coli; and the modality (distribution) of induction among populations of cells. L-Mannose was found to be the most useful orthogonal inducer, providing an even greater range of induction than the native inducer Lrhamnose, and crucially, allowing sustained induction instead of transient induction. These findings address the key limitation of the rhaBAD expression system, and suggest it may now be the most suitable system for many applications

Experimental and analytical investigation of flow through rocket pump inducer

The characteristics of a rocket pump inducer are discussed. The effect of the pumping requirements on the blade configuration is analyzed. The effects of viscosity on blade design were determined by tests of a four bladed inducer operated in air at a flow coefficient of 0.065. The fluid properties were measured at the exit of the inducer using conventional and hot wire probes. The experimental results and the method of predicting the outlet tangential velocity and head rise are discussed

Panel Discussion on Inducer Design Criteria

This article reports a panel discussion titled Inducer Design Criteria presented at the 9th International Symposium on Transport Phenomena and Dynamics of Rotating Machinery (ISROMAC-9). The presentations of the panelists and the subsequent discussions are summarized. It is shown that cavitation instabilities are major problems in modern turbopumps and that design criteria to eliminate them are needed. Available design methods for inducers and marine propellers are reviewed, and new criteria to enhance stability are proposed. The current status of CFD is reviewed and an example of successful application is shown. Discussions of several specific topics are reported and future research needs are noted

Twin-spool turbopumps for ''low'' net positive suction pressure operations

Modified single-shaft turbopump incorporates inducer and main pump, each separately driven at different speeds through coaxial-shaft arrangement. Inducer operates at low speed for low net positive suction pressure, main pump operates at high speed to generate high pressure. This arrangement requires no external control for the inducer

An investigation of tandem row high head pump inducers Interim report

Streamline calculations for tandem row high head pump inducer

A multifrequency instability of cavitating inducer systems

Recent testing of high speed cavitating turbopump inducers has revealed the existance of more complex instabilities than the previously-recognized cavitating surge and rotating cavitation. This paper explores one such instability which is uncovered by considering the effect of a downstream asymmetry such as a volute on a rotating disturbance similar to (but not identical to) that which occurs in rotating cavitation. The analysis uncovers a new instability which may be of particular concern because it occurs at cavitation numbers well above those at which conventional surge and rotating cavitation occur. This means that it will not necessarily be avoided by the conventional strategy of maintaining a cavitation number well above the performance degradation level. The analysis considers a general surge component at an arbitrary frequency, ω, present in a pump rotating at frequency, Ω, and shows that the existence of a discharge asymmetry gives rise not only to beat components at frequencies, Ω − ω and Ω + ω (as well as higher harmonics) but also to circumferentially-varying components at all these frequencies. In addition, these interactions between the frequencies and the basic and complementary modes lead to “coupling impedances” that effect the dynamics of each of the basic frequencies. We evaluate these coupling impedances and show not only that they can be negative (and thus promote instability) but also are most negative for surge frequencies just a little below Ω. This implies potential for an instability involving the coupling of a basic mode with a frequency around 0.9Ω and a low frequency complementary mode about 0.1Ω. We also examine how such an instability would be manifest in unsteady pressure measurements at the inlet to and discharge from a cavitating pump and establish a “footprint” for the recognition of such an instability

Observations on Instabilities of Cavitating Inducers

Hydraulic systems involving cavitating turbomachines are known to be susceptible to instabilities at certain critical operating conditions. Two distinct classes of cavitating inducer instabilities have been reported in the literature (Refs. 1-6). The purpose of this note is to report on some preliminary observations of these phenomena. The experiments were performed in the Dynamic Pump Test Facility (DPTF) at the California Institute of Technology (Refs. 7, 8). Results will be presented for two different inducers operating at different flow coefficients, [symbol] ([symbol]= mean axial velocity/inducer tip velocity- [equation]) and cavitation numbers, [symbol] ([symbol]=[equation]; where [equation] are the inlet and vapor pressures, and [symbol] is the liquid density). In general, the instabilities occurred just before the head breakdown. After head breakdown, the system tended to become stable again, although there were some indications of a second region of instability at very small cavitation numbers. Impeller IV is a quarter scale model of the Low Pressure Oxidizer Turbo-Pump (LPOTP) of the space shuttle main engine (Refs. 7, 8). The cavitation performance of this impeller is presented in Figure 1. Some of the mean operating states for which large, constant amplitude oscillations occurred in all the pressures and mass flow rates are indicated by stars. The cavitation in each of the blade passages oscillated in unison. This unstable behavior is termed auto-oscillation. The frequency of the auto-oscillations ranged from 28 to 35 Hz. As might be expected, there does exist a marginal region of operation for which the auto-oscillations have a time varying amplitude. These non-steady oscillations occurred as sporadic bursts of auto-oscillation. It was this feature that makes the boundaries of the auto-oscillation region difficult to define. In addition to the auto-oscillation observations on Impeller IV, two instances of "rotating cavitation" were observed and are labeled by boxes in Figure 1. The presence of rotating cavitation was determined by means of a stroboscope slaved to the rotational speed of the inducer. Rotating cavitation appeared as a non-stationary cavitation patterns which rotated with respect to the "fixed" inducer. (More recent testing has also revealed the existence of a stationary form of rotating cavitation sometime referred to as alternate blade cavitation.) The large amplitude disturbances in the upstream pressure and mass flow rates which characterized auto-oscillation were not observed during rotating cavitation. This suggests the rotating cavitation is most intimately associated with the dynamic characteristics of the cavitating inducer itself irrespective of the hydraulic system in which it resides

Spatial Facilitation by Color and Luminance Edges: Boundary, Surface, and Attentional Factors

The thresholds of human observers detecting line targets improve significantly when the targets are presented in a spatial context of collinear inducing stimuli. This phenomenon is referred to as 'spatial facilitation', and may reflect the output of long-range interactions between cortical feature detectors. Spatial facilitation has thus far been observed with luminance-defined, achromatic stimuli on achromatic backgrounds. This study compares spatial facilitation with line targets and collinear, edge-like inducers defined by luminance contrast to spatial facilitation with targets and inducers defined by color contrast. The results of a first experiment show that achromatic inducers facilitate the detection of achromatic targets on gray and colored backgrounds, but not the detection of chromatic targets. Chromatic inducers facilitate the detection of chromatic targets on gray and colored backgrounds, but not the detection of achromatic targets. Chromatic spatial facilitation appears to be strongest when inducers and background are isoluminant. The results of a second experiment show that spatial facilitation with chromatic targets and inducers requires a longer exposure duration of the inducers than spatial facilitation with achromatic targets and inducers, which is already fully effective at an inducer exposure of 30 milliseconds only. The findings point towards two separate mechanisms for spatial facilitation with collinear form stimuli: one that operates in the domain of luminance, and one that operates in the domain of color contrast. These results are consistent with neural models of boundary and surface formation which suggest that achromatic and chromatic visual cues are represented on different cortical surface representations that are capable of selectively attracting attention. Multiple copies of these achromatic and chromatic surface representations exist corresponding to different ranges of perceived depth from an observer, and each can attract attention to itself. Color and contrast differences between inducing and test stimuli, and transient responses to inducing stimuli, can cause attention to shift across these surface representations in ways that sometimes enhance and sometimes interfere with target detection.Defense Advanced Research Projects Agency and Office of Naval Research (N00014-95-1-0409, N00014-95-1-0657

Analytical and experimental study of mean flow and turbulence characteristics inside the passages of an axial flow inducer

The effort conducted to gather additional understanding of the complex inviscid and viscid effects existing within the passages of a three-bladed axial flow inducer operating at a flow coefficient of 0.065 is summarized. The experimental investigations included determination of the blade static pressure and blade limiting streamline angle distributions, and measurement of the three components of mean velocity, turbulence intensities and turbulence stresses at locations inside the inducer blade passage utilizing a rotating three-sensor hotwire probe. Applicable equations were derived for the hotwire data reduction analysis and solved numerically to obtain the appropriate flow parameters. Analytical investigations were conducted to predict the three-dimensional inviscid flow in the inducer by numerically solving the exact equations of motion, and to approximately predict the three-dimensional viscid flow by incorporating the dominant viscous terms into the exact equations. The analytical results are compared with the experimental measurements and design values where appropriate