Increase Of Supply Pressure Research Articles

Study on bearsing capacity and rigidity of surface throttling bearing

Abstract Based on the lubrication principle and Reynolds theory, the influence of the pressure field and structural parameters on the bearing characteristics of the surface throttle bearing is analyzed and studied by using the finite difference method. The results show that the surface throttling bearing has obvious static bearing characteristics when the shaft is not rotating; The dynamic pressure effect of oil wedge load can be seen obviously when the shaft rotates. With the increase of radius gap h0, the bearing capacity and rigidity will decrease significantly. The increase of oil supply pressure will reduce bearing capacity and rigidity. With the increase of length-diameter ratio L ¯ , the rigidity will be improved.

Numerical Analysis on the Static Performance of Gas Journal Bearing by Using Finite Element Method

In this paper, finite element method is used to calculate the static performance of gas journal bearing, in which rotation speed term is introduced into the stiffness matrix of linear triangular element to realize the performance calculation of the bearing with rotation speed. The results indicate that the average gas film thicknesses corresponding to the maximum load capacity and stiffness, and the minimum attitude angle increase with the growth of orifice diameter. Load capacity and stiffness significantly improved with the increase of rotation speed, eccentricity ratio and supply pressure when the bearing has thin average gas film thickness. Attitude angle increases with the growth of rotation speed, while the growth rate slows down or even decreases at high speed. The most effective way of reducing attitude angle is to increase supply pressure. It can be found that rotation speed affects attitude angle through changing gas pressure difference between two orifices, while other parameters have the same effect by changing gas pressure at orifice outlet.

Experimental investigation on diffusion and fountain behavior of bubble plumes in quiescent water

Bubble plumes are a common phenomenon, which are simultaneously hazardous and exploitable. Diffusion and fountain behavior, regarded as significant characteristics of bubble plumes, were investigated in this experiment utilizing high-speed photography and image processing techniques within a rectangular bubble column crafted from organic glass. The diffusion, coalescence, and collapse phenomena of bubble plumes were visualized during their ascent under varying gas flow rates in quiescent water. Furthermore, the influence of gas supply pressure, flow rate, and water depth on the fountain height was examined. The research findings demonstrate that an increase in gas supply pressure and flow rate leads to a subsequent rise in fountain height once the bubble plume reaches the surface. Conversely, a reduction in the fountain height is observed with an increase in the depth of gas release. Through the application of a dimensionless analysis method, the factors influencing the fountain height were correlated, resulting in the proposal of a relationship formula for predicting fountain height. The predicted outcomes exhibited good consistency with the data reported in this experiment.

Evaluation of the Parameters of the Dispersed Stream Generated by Various Types of Water Nozzles

Aim: The purpose of the research was to determine the parameters of the micro- and macro-structure of the streams generated by nozzles of different types, and to identify potential applications of the tested water nozzles, including firefighting and air pollution removal. Introduction: TF6 FCN, TF6 V, NF 15 and CW 50 water nozzles were tested. At supply pressures of 0.2 MPa, 0.4 MPa and 0.6 MPa, the basic parameters of micro- and macrostructure of the streams were measured and determined: flow rate, spray angle, mass distribution of liquid on the surface (spray intensity), non-uniformity of spray density distribution, and average droplet diameters and spray spectrum. A sputter spectrum analyser, using the photoelectric method, was used to determine the microstructural parameters of the stream. Project and methods: Badaniom poddano dysze wodne TF6 FCN, TF6 V, NF 15 oraz CW 50. Przy ciśnieniu zasilania równym 0,2 MPa, 0,4 MPa oraz 0,6 MPa zmierzono i wyznaczono podstawowe parametry mikro- i makrostruktury strumieni: natężenie przepływu, kąt rozpylenia, rozkład masowy cieczy na powierzchni (intensywność zraszania), nierównomierność rozkładu gęstości zraszania oraz średnie średnice kropel i widmo rozpylenia. Do określenia paramentów mikrostrukturalnych strumienia zastosowano analizator widma rozpylenia, wykorzystujący metodę fotoelektryczną. Results: The tested nozzles generated dispersed streams with different parameters. Among the analysed nozzles, the highest degree of dispersion was obtained for the TF 6 FCN sample, whose average Sauter mean diameter (SMD) reached a value of 217.3 μm. In comparison, for the NF15 nozzle this parameter was 945 μm. The spray spectra indicate a high homogeneity of water dispersion in the stream produced by the nozzles TF 6 FCN and CW 50. From the distribution of mass sprinkling density, the CW 50 nozzle shows the greatest uniformity of spraying. At the same time, however, it reports a small amount of water, since the value of the spray density for this product did not exceed 100 g/( m2 · s), while for the NF 15 nozzle it was more than 2,700 g/( m2 · s). The obtained spray angles were close to those declared by the nozzle manufacturer. In the tests of all samples, a slight effect of supply pressure on the values of this parameter was observed. Conclusions: Among other things, the tests made it possible to conclude that in the range of supply pressures of 0.2÷0.6 MPa, the values of disperse angle and spray area of the analysed nozzles were constant or the recorded differences were insignificant. In addition, it was determined that in the case of nozzles with full spray cones, an increase in supply pressure (within the range of declared operating values) has little effect on changing the parameters of the micro- and macro-structure of the stream. The conducted tests showed the potential use of two nozzles (TF6 FCN, CW 50) in low-pressure fog extinguishing systems producing fog with SMD droplet diameters > 200 μm. For the absorption of hazardous substances, it is recommended to use nozzles with a large spray angle and a full spray cone, which, as tests have shown, produce uniform streams with small droplet diameters. Keywords: water nozzles, water spray, spray spectrum, mass spray density, water mist

Influence of measurement parameters on hydrogen absorption properties of hydrogen storage alloys

ABSTRACT To predict real-time performance of metal hydride-based systems, La0.9Ce0.1Ni5 and LaNi4.7Al0.3 alloys are opted to investigate the influence of operating temperature and supply pressure on absorption kinetics. For the same, the pressure ratio is varied from 1.5 to 4 by keeping the temperature constant. Later, the operating temperature is varied (20–80°C) for the above range of pressure ratio. The study revealed that the absorption kinetics of metal hydrides is substantially influenced by operating temperature and supply pressure. It is observed that with an increase in pressure ratio (1.5, 2, 2.5, 3, and 3.5), the hydrogen supply pressure increases (9.75, 13, 16.25, 19.5, and 22.75), which creates high driving potential consequently results in faster reaction rates. However, increase in operating temperature (20°C and 40°C) at constant supply pressure (25 bar) results in slower reaction rates due to decrease in driving potential because the equilibrium pressure of La0.9Ce0.1Ni5 is higher at high temperature. The similar effect is obtained for LaNi4.7Al0.3. The experimental measurements are carried out using an in-house Sievert’s apparatus and are compared with numerical results obtained through a mathematical model that results in good agreement.

Secondary Frequency Regulation Control Strategy with Electric Vehicles Considering User Travel Uncertainty

The premise of electric vehicles (EVs) participating in the frequency regulation (FR) of power systems is to satisfy the charging demands of users. In view of problems such as the uncertainty of EV users’ departure time and the increase in power supply pressure due to disordered charging in the frequency regulation process of EV clusters, a secondary frequency regulation control strategy with EVs considering user travel uncertainty is proposed. Firstly, EV charging history was analyzed, a reliability parameter was introduced to describe the user travel uncertainty, and an individual EV controllable domain model based on reliability correction was constructed. Then, EV clusters were grouped according to charging urgency and state of charge (SOC), and the controllable capacity of EV clusters was determined. Finally, EV frequency regulation capability parameters and charging urgency parameters were defined to determine the EV frequency regulation priority list, combined with the EV state grouping and priority list, and the EV cluster frequency control strategy was proposed. The simulation results show that the proposed strategy can satisfy the charging demands of users under uncertain travel conditions, reduce the power supply pressure of the power system caused by EVs entering the forced charging state, and effectively suppress frequency deviation.

Static Load Characteristics of Hydrostatic Journal Bearings: Measurements and Predictions.

Hydrostatic bearings for liquid rocket engine turbopumps provide distinctive advantages, including high load capacity even with low viscosity cryogenic fluid and extending life span by minimizing friction and wear between rotor and bearing surfaces. Application of hydrostatic bearings into turbopumps demands a reliable test database with well-quantified operating parameters and experimentally validated accurate performance predictive tools. The present paper shows the comprehensive experimental data and validation of predicted static load characteristics of hydrostatic journal bearings lubricated with air, water, and liquid nitrogen. Extensive experiments for static load characteristics of hydrostatic bearings are conducted using a turbopump-rotor-bearing system simulator while increasing supply pressure (Ps) into the test bearings. The test results demonstrate notable effects of the test fluids and their temperatures, as well as Ps, on the bearing performance. In general, the measured bearing flow rate, rotor displacement, and stiffness of the test bearings steadily increase with Ps. The static load bearing characteristics predictions considering flow turbulence and compressibility matched well with the experimental results. The work with independent test data and engineering computational programs will further the implementation of hydrostatic bearings in high-performance turbopump shaft systems with improved efficiency and enhanced reusability of liquid rocket engine sub-systems.

Investigation of optimal selection and atomizing characteristics of nozzles for ultrasonic dry-mist dust suppression system

ABSTRACT In order to provide insightful guidance for the selection of nozzles and the determination of operating conditions of ultrasonic dry-mist dust suppression system, this study collected six different types of ultrasonic dry-mist nozzles and investigated their atomizing characteristics in depth. Through comparison, the optimal nozzles were applied to engineering site and the dust suppression performance was measured. According to the present research results, the spraying ranges of No. 3, No. 5 and No. 6 nozzles among six different types of nozzles are below 170 cm, suggesting these nozzles are not suitable for far-distance dust suppression. Among the rest three types of nozzles, No. 4 nozzle (ST-47 nozzle) performs best in terms of overall performance, which can not only possess great spraying range but also produce the droplets at the dry-mist level size. Therefore, No. 4 nozzle is applicable to dry-mist dust suppression system in most cases. As the air supply pressure increases, the air flow rate of ST-47 nozzle increases gradually in exponential form while the water flow rate drops exponentially, accompanied with constant increasing ratio of gas-to-liquid flow rate. As the water supply pressure increases, the air flow rate of ST-47 nozzle decreases gradually in exponential form, while the water flow rate increases exponentially, accompanied with constant decreasing ratio of gas-to-liquid flow rate. As regard to the other atomizing parameters, the spraying range increases as the increasing air supply pressure but decreases as the increasing water supply pressure; both the droplet size and atomizing angle decrease as the increasing air supply pressure but increase as the increasing water supply pressure. The optimal operating condition for ST-47 ultrasonic dry-mist nozzle was determined as p L = 0.1 MPa and p air = 0.5 MPa. Under that optimal operating condition, the total dust and respirable dust suppression efficiencies after the application of ultrasonic dry-mist dust suppression system during coal transport on the belt can reach up to 94.1% and 96.1%, respectively.

Research on the operation mechanism and stability of marine textured directional valve

Based on the vibration force analysis of the marine electromagnetic directional valve and Newton’s Second Law, the mathematical model of the displacement of the valve rod under vibration excitation state is established. The influence of vibration parameters and viscous damping coefficient on its operation stability is calculated and analyzed. Results show that the vibration stability can be improved by increasing the clearance viscous damping of the directional valve, and the textured surface affecting on the viscous force and flow resistance characteristics. All of these provide a basis for stability optimization. The on-board experiment of marine electromagnetic directional valve in real-time working condition is operated, the performance difference between the textured and untextured valve is analyzed. The results show that the pressure adjustment time and vibration impact amplitude of two kinds of directional valves decrease with the increase of oil supply pressure, and increase with the increase of navigation speed. The standard deviation of flow fluctuation of untextured directional valve increases with the increase of oil supply pressure, while the flow fluctuation of micro-textured directional valve first decreases and then increases. The unique interface characteristics of the micro-textured directional valve make the pressure adjustment time, the standard deviation of flow pulsation, and the vibration impact amplitude of the micro-textured valve smaller than that of the untextured one.

Experimental investigation on flow characteristics of compressible oscillating jet

An experimental study was performed to investigate the characteristics of a self-sustained oscillating jet emitted from a double feedback channel fluidic oscillator under high pressure inlet conditions. The working fluid was N2 gas from a portable liquid nitrogen tank. The pressure, temperature, and flow rate were measured, and z-type schlieren visualization was performed to study the high-frequency oscillating jet at nozzle pressure ratios (NPRs) of 4–16. A proper orthogonal decomposition (POD) technique was performed on schlieren images, and a Fast Fourier transform was performed on time coefficients of POD modes to calculate the frequency of oscillations. The results show that for the examined NPRs, the frequency of the oscillating jet is independent of the pressure and flow rate, which contrasts with previous studies. However, the flow behavior varies when changing the NPR. The frequency did not increase with increasing supply pressure. In order to find the main reason for the fixed frequency, a second-order mass spring system was assumed. An equation is also proposed for obtaining the resonance frequency of the double feedback fluidic oscillator.

Experimental study on the lubrication characteristics of water-lubricated rubber bearings at high rotating speeds

A test rig is designed to study the lubrication characteristics of water-lubricated rubber bearings. The film pressure signal quality is improved by installing signal conditioners inside the hollow shaft. Four triaxial force sensors are adopted to measure the bearing load in two directions simultaneously. The experimental results show that the film pressure drops rapidly downstream of the minimum clearance. The water film can bear a certain negative pressure without cavitation. As the rotating speed increases, the valley value of the film pressure decreases, and the peak value increases. The increase of water supply pressure improves the hydrostatic pressure, thereby, the film pressure rises over the whole circumference. Different from the laminar flow, the bearing load increases faster as the rotating speed increases, indicating a turbulent flow at high rotating speeds.

Model and Experimental Verification of the Dynamic Forced Performance of a Tightly Sealed Squeeze Film Damper Supplied With a Bubbly Mixture

Abstract Practice and experiments with squeeze film dampers (SFDs) sealed with piston rings (PRs) show the lubricant exits through the PR slit, i.e., the gap made by the PR abutted ends when installed, forced as a jet during the portion of a rotor whirl cycle generating a positive squeeze film pressure. In the other portion of a whirl cycle, a subambient dynamic pressure ingests air into the film that mixes with the lubricant to produce a bubbly mixture. To reduce persistent air ingestion, commercial air breathing engines utilizing PRSFDs demand of a sufficiently large lubricant supply pressure (Ps), and hence a larger flow rate that is proportional to the journal squeeze velocity (vs = amplitude r × frequency of motion ω). The stringent requirement clearly limits the applicability and usefulness of SFDs. This paper presents a computational physics model for a sealed-end SFD operating with a mixture and delivers predictions benchmarked against profuse laboratory test data. The model implements a Reynolds equation adapted for a homogeneous bubbly mixture, includes temporal fluid inertia effects, and uses physics-based inlet and outlet lubricant conditions through feed holes and PR slit, respectively. In the experiments for model validation, a SFD damper, 127 mm in diameter D, film land length L = 25.4 mm (L/D = 0.2), and radial clearance c = 0.371 mm, is supplied with an air in ISO VG2 oil bubbly mixture of known gas volume fraction (GVF), zero (pure oil) to 50% in steps of 10%. The mixture supply pressure varies from Ps = 2.06 bar-g (30 psig) to 6.20 bar-g (90 psig). Located in grooves at the top and bottom of the journal, a PR and an O-ring (OR) seal the film land. The OR does not allow any oil leakage or air ingestion; hence, the supplied mixture discharges through the PR slit into a vessel submerged within a large volume of lubricant. Dynamic load tests with a single frequency ω, varying from 10 Hz to 60 Hz, produce circular centered orbits (CCO) with amplitude r = 0.2c. The measurements record the exerted forces and journal motions and an analysis delivers force coefficients, damping and inertia, representative of the exerted frequency range. The model predicts the pressure field and evolution of the GVF within the film land and, in a simulated process replicating the experimental procedure, delivers representative force coefficients. For all Ps conditions, both predictions and tests show the SFD added mass coefficients significantly decrease as the inlet GVF (βs) increases. The experimentally derived damping coefficients do not show a significant change, except for tests with the largest concentration of air (βs = 0.5). The predicted damping differs by 10% with the test derived coefficient which does not readily decrease as the inlet GVF (βs) increases. The added mass coefficients, test and predicted, decrease with βs, both being impervious to the magnitude of supply pressure. The test PRSFD shows a quadrature stiffness due to the sliding friction between the PR being pushed against the journal. An increase in supply pressure exacerbates this unique stiffness that may impair the action of the squeeze film to dissipate mechanical energy. The comprehensive test results, first of their kind, demonstrate that accurate modeling of SFDs operating with air ingestion remains difficult as the flow process and the paths of its major components (air and liquid) are rather complex.

Effect of water supply pressure on atomization characteristics and dust-reduction efficiency of internal mixing air atomizing nozzle

As a new type of nozzle, the internal mixing air atomizing nozzle has been widely used in the field of dust reduction via spraying. In this study, the effect of water supply pressure on the atomization characteristics and dust-reduction efficiency of the internal mixing air atomizing nozzle was investigated. Firstly, the FLUENT software was used to simulate the flow field inside and outside the nozzle under different water supply pressures. The numerical simulation results showed that as the water supply pressure increased, the internal pressure and water flow velocity in the mixing chamber of the nozzle increased while the air flow rate decreased sharply, resulting the continuous decrease in the relative velocity between gas and liquid. Meanwhile, as the water supply pressure increased, the fragmentation scale of the liquid jet at the outlet of the nozzle was prolonged and the atomization of the liquid was limited. Secondly, based on the custom-developed dust reduction experimental system via spraying, the atomization characteristics of the nozzle were investigated. According to the experimental results, when the water supply pressure increased, the water flow rate and air flow rate of the nozzle had exponential increase and decrease, respectively. As the water supply pressure increased, the range, droplet volume fraction, droplet size, and velocity all increased, while the atomization angle first increased and then decreased. Finally, the dust reduction experiment via spraying was performed under different water supply pressures. The results showed that with the increase of water supply pressure, the dust-reduction efficiency for both the total dust and the respirable dust first increased and then decreased.

Influence of air supply pressure on atomization characteristics and dust-suppression efficiency of internal-mixing air-assisted atomizing nozzle

In this study, the effect of air supply pressure on atomization characteristics and dust-suppression efficiency of internal-mixing air-assisted atomizing nozzle was investigated. Firstly, the FLUENT software was employed to simulate the flow field inside the nozzle and near the outlet of the nozzle under different air supply pressures. The numerical simulation results showed that as the air supply pressure increased, the pressure and air flow velocity inside the mixing chamber of the nozzle increased dramatically, while the water flow velocity at the water injection hole decreased. At the same time, with the increase of air supply pressure, the fragmentation scale of the liquid jet was continuously shortened, thus the primary atomization of the liquid was more sufficient. Secondly, the custom-developed dust suppression experimental system via spraying was used to investigate the atomization characteristics of the nozzle. According to the experimental results, when the air supply pressure increased, both the droplet size and the droplet volume fraction decreased, the air flow rate increased exponentially, and the water flow rate decrease linearly. In addition, as the air supply pressure increased, the atomization angle, the droplet velocity and the droplet number density first increased and then decreased. Finally, the dust-reduction experiment via spraying was performed under different air supply pressures. The results showed that the dust-suppression efficiency of total dust and respirable dust had a trend of first increasing and then decreasing with the increase of the air supply pressure. The classification efficiency of dust suppression via spraying first increased and then decreased with the increase in the dust particle diameter. Furthermore, as the droplet size decreased, the peak particle diameter decreased accordingly.

Experimental Research on the JT Cycle of Hybrid 4.5K JT Cryocooler

Key Laboratory of Space Energy Conversion Technologies of TIPC, CAS has developed a 4.5K Joule-Thomson (JT) cryocooler precooled by a multistage pulse tube cooler. In this paper, series of experimental research is carried out to explore the performance of the JT cooler at different operating conditions. When only the power consumption of JT compressors is considered, the coefficient of performance (COP) of the JT cycle is proposed to evaluate the performance of JT cycle. Experimental research is carried out to investigate the influence of supply pressure and JT orifice on cooling capacity and especially the COP of JT cooler. Experimental results suggest that cooling power of JT cooler increases as supply pressure increases and higher COP are gained because of rising flow resistance of JT orifice. Then JT orifices of different diameters are experimentally studied to explore the effect of flow resistance of JT orifice on the performance of JT cooler.

Parametric Studies on LaNi4.7Al0.3 based Hydrogen Storage Reactor with Embedded Cooling Tubes

Abstract This study reports the investigative conclusions of parametric studies conducted to understand the effect of operating parameters on absorption and desorption characteristics of LaNi4.7Al0.3 metal hydride system for thermal management applications. Reactor with improved design containing 55 embedded cooling tubes is fabricated and filled with 4 kg of metal hydride alloy. Using water as heat transfer fluid (HTF), effects of supply pressure, HTF temperature and HTF flow rate on absorption and desorption characteristics of the reactor are analyzed. Increasing supply pressure leads to prominent improvement in absorption capacity while the increase in HTF temperature enhanced desorption performance. At 20 bar and 20 °C, 46.2877 g of hydrogen (1.16 wt%) was absorbed resulting in total energy output of 707.3 kJ for 300 s. During desorption at 80 °C with water flow rate of 8 lpm, heat input of 608.1 kJ for 300 s resulted in 28.5259 g of hydrogen desorption.

Study on the dynamic and static characteristics of gas static thrust bearing with micro-hole restrictors

For the dynamic and static characteristics of the gas static thrust bearing with micro-hole restrictors, a gas static thrust bearing with micro-hole restrictors was designed, manufactured, and experimented. The static stiffness and stability under different gas supply pressure and film thickness were studied. The following conclusions were drawn: the bearing static stiffness increases first and then decreases with the increase of gas film thickness, the bearing static stiffness increases with the increase of the supply pressure. The supply pressure and the film thickness have different effects on the micro-vibration of the bearing, as the supply pressure increases, the vibration amplitude of the bearing becomes larger, but the peak frequency of the bearing vibration is basically the same. As the thickness of the film increases, the vibration amplitude of the bearing increases first and then decreases, and the peak frequency of the bearing vibration has changed. The study provides an experimental basis for the practical application of the gas static thrust bearing with micro-hole restrictors under micro gas film thickness.

A semianalytical method for studying the performances of aerostatic thrust bearing

The solution of Reynolds equation and computational fluid dynamics are widely employed for the lubrication performance analysis of aerostatic thrust bearing. However, the solution of Reynolds equation may be inaccurate and cannot present detailed performance near orifice, while computational fluid dynamics method has low computational efficiency with time consumption in mesh generation and solving Navier–Stokes equations. In order to overcome the drawbacks of Reynolds equation and computational fluid dynamics, based on the method of separation of variables, a semianalytical method is developed for describing the characteristics of aerostatic bearings available. The method of separation of variables considering the initial and viscous effect is more accurate than the Reynolds equation and can present detailed performance near orifice in the aerostatic thrust bearings, while method of separation of variables has great computational efficiency compared to computational fluid dynamics. Meanwhile, the pressure distribution calculated by method of separation of variables is compared to the published experimental data and the results obtained by computational fluid dynamics. The comparative results indicate validity of the method. Furthermore, the influences of flow and geometry parameters, such as supply pressure, orifice diameter, film thickness, and bearing radius, on the characteristics of aerostatic thrust bearings with single orifice are studied. The results show that there exists pressure depression phenomenon near orifice. The depression phenomenon is strengthened with increase of film thickness and supply pressure and decrease of orifice diameter and bearing radius, while the maximum speed increases with strengthening of pressure depression due to decrease of minimum local pressure near orifice. Moreover, the bearing capacity increases with increase of supply pressure, orifice diameter, and bearing radius and decreases with increase of film thickness, while mass flow rate increases with supply pressure, orifice diameter, and film thickness and it is not sensitive to bearing radius.

Experimental Force Coefficients for Two Sealed Ends Squeeze Film Dampers (Piston Rings and O-Rings): An Assessment of Their Similarities and Differences

Squeeze film dampers (SFDs) in aircraft engines effectively aid to reduce rotor motion amplitudes, in particular when traversing a critical speed, and help to alleviate rotor whirl instabilities. The current work is a long-term endeavor focused on quantifying the dynamic force performance of practical SFDs, exploring novel design damper configurations, and producing physically sound predictive SFD models validated by experimental data. Piston rings (PRs) and O-rings (ORs), commonly used as end seals in SFDs for commercial and military gas turbine engines, respectively, amplify viscous damping in a short physical length and while operating with a modicum of lubricant flow. This paper presents experimental force coefficients (damping and inertia) for two identical geometry SFDs with end seals, one configuration hosts PRs, and the other one ORs. The test rig comprises a stationary journal and bearing cartridge (BC) hosting the SFD and supported on four elastic rods to emulate a squirrel cage. The damper film land length, diameter, and clearance are L = 25.4 mm, D = 5L, and c = 0.373 mm (D/c = 340), respectively. A supply feeds ISO VG 2 oil to the film land at its middle plane through either one hole or three holes, 2.5 mm in diameter, 120 deg apart. In the PRSFD, the lubricant exits through the slit opening at the ring butted ends. The ORs suppress oil leakage; hence, lubricant evacuates through a 1 mm hole at ¼ L near one journal end. The ORs when installed add significant stiffness and damping to the test structure. The ORSFD produces 20% more damping than the PRSFD, whereas both sealed ends SFDs show similar size added mass. For oil supplied at 0.69 bar(g) through a single orifice produces larger damping, 60–80% more than when the damper operates with three oil feedholes. A computational model reproducing the test conditions delivers force coefficients in agreement with the test data. Archival literature calls for measurement of a single pressure signal to estimate SFD reaction forces. For circular centered orbits (CCOs), the dynamic pressure field, in the absence of any geometrical asymmetry or feed/discharge oil condition, “rotates” around the bearing with a speed equal to the whirl frequency. The paper presents force coefficients estimated from (a) measurements of the applied forces and ensuing displacements, and (b) the dynamic pressure recorded at a fixed angular location and “integrated” over the journal surface. The first method delivers a damping coefficient that is large even with lubricant supplied at a low oil supply pressure whereas the inertia coefficient increases steadily with feed pressure. Predictions show good agreement with the test results from measured forces and displacements, in particular the added mass. On the other hand, identified damping and inertia coefficients from dynamic pressures show a marked difference from one pressure sensor to another, and vastly disagreeing with test results from the first method or predictions. The rationale for the discrepancy relies on local distortions in the dynamic pressure fields that show zones of oil vapor cavitation at a near zero absolute pressure and/or with air ingestion producing high frequency spikes from bubble collapsing; both phenomena depend on the magnitude of the oil supply pressure. An increase in lubricant supply pressure suppresses both oil vapor cavitation and air ingestion, which produces an increase of both damping and inertia force coefficients. No prior art compares the performance of a PRSFD vis-à-vis that of an ORSFD. Supplying lubricant with a large enough pressure (flow rate) is crucial to avoid the pervasiveness of air ingestion. Last, the discussion on force coefficients obtained from two distinct methods questions the use of an oversimplifying assumption; the dynamic pressure field is not invariant in a rotating coordinate frame.

Measurements of the Rotordynamic Response of a Rotor Supported on Porous Type Gas Bearing

A test rig is built in this study to measure the rotordynamic response of a rotor supported on porous-type gas bearings. A rotor with a double impulse turbine at one end is driven by compressed air and supported on two porous type journal gas bearings and a pair of bump-type thrust gas bearings. The rotor is accelerated to ∼25 krpm and coasted down in the test. The rotor dynamic response is measured for different bearing supply pressures (i.e., 0.40 MPa, 0.45 MPa, and 0.50 MPa) and imbalance masses (i.e., 85 mg, 150 mg, and 215 mg). Synchronous and subsynchronous amplitudes are extracted from the rotor responses. The critical speed increases as the bearing supply pressure increases, but the damping ratio decreases. The onset speed of subsynchronous motion increases, and the subsynchronous amplitude decreases as the bearing supply pressure increases. The deceleration time is more than 5 min for a bearing supply pressure of 0.5 MPa, which reveals the very low drag friction of the porous gas bearings. The synchronous amplitude increases as the imbalance increases for all the tested bearing supply pressures. The critical speeds for different imbalances are almost the same, except for the out-of-phase imbalance condition under a bearing supply pressure of 0.50 MPa, in which the critical speed increases as the imbalance increases. The normalized synchronous amplitude shows the rotor-bearing system behaves almost in a linear fashion for all in-phase imbalance conditions. Nonlinear behavior is shown around the critical speed for the 215 mg out-of-phase imbalance condition under a bearing supply pressure of 0.50 MPa. The onset speed of the subsynchronous motion decreases as the imbalance increases under the in-phase imbalance condition. The predominant mode of vibration changes from cylindrical to conical and then back to cylindrical as the rotor speed decreases during the coast down test for the in-phase imbalance conditions. However, the rotor vibration mode is predominantly conical during the whole coast down test for the out-of-phase imbalance conditions.