IN-STALL COMPRESSOR PERFORMANCE AND THE EFFECTS OF REYNOLDS NUMBER

Previous research into axial compressor stall has mainly focused on stall inception and methods to extend the stable operating range. This paper considers the performance of an axial compressor beyond stall and investigates how the characteristics of stall cells depend on Reynolds number. An experimental study has been conducted using a single-stage axial compressor capable of operating across the Reynolds number range of 10,000 – 100,000. Detailed unsteady measurements have been used to measure the behaviour across a range of in-stall flow coefficients. These measurements have been used to extract the stall hysteresis and to determine the size, speed, number, and spanwise extent of the stall cells. The results show that for the stalled compressor, as Reynolds number increases, the size of the minimum stable stall cell decreases. This means that a larger change in throttle area is needed to reduce the stall cell down to a size where the compressor can recover from stall. At the design Reynolds number, the number of stall cells that form transitions from one, to two, and then to four stall cells as the flow coefficient is reduced. At lower Reynolds numbers, the two-stall-cell state becomes unstable; instead, a single stall cell transitions directly into five stall cells. As the number of stall cells increases, so do the speed of the stall cells and the total size. Further reductions in the flow coefficient cause an increase in the total size and a decrease in the stall cell speed.

Flow Characteristics of the Nozzle Blade Cascade in the Mode of the Joint Operation with the Radial Diffuser

The obtained research data are given for the nozzle cascade used by a small-size gas turbine of an average fanning in combination with the radial diffuser. Aerodynamic characteristics of the nozzle blade cascade were determined in a wide range of a change in the Reynolds number varying from 4∙105 to 106 and the reduced velocity varying in the range of 0.4 to 1.13. The flow rate coefficient of the nozzle cascade was derived for all modes using the integral methods and the drainages behind the cascade. The kinetic energy loss coefficient and the flow angles were calculated using the measurement data of flow parameters in three control modes that were obtained due to the use of orientable pneumometric probes. When the expansion degree of the convergent –divergent annular duct behind the cascade is equal to 1.43 the flow in the narrow section of this duct is “enlocked” in the mode when the reduced velocity behind the cascade is equal to 1.127. At such velocity the Reynolds number 106 is self-similar for the flow rate coefficient. At lower values of Reynolds number, the decrease of it is accompanied by an intensive decrease in the flow rate coefficient for all the values of the reduced velocity. For the Reynolds number lower than 7∙105 an increase in the velocity results in a decreased flow rate coefficient. When this number exceeds 8∙105 an increase in the velocity results in an increase of the flow coefficient up to the moment when the flow is “enlocked” in the nozzle cascade.

Verification and Validation of CFD Modeling for Low-Flow-Coefficient Centrifugal Compressor Stages

In this paper, the numerical model of a centrifugal compressor low-flow stage is verified. The gaps and labyrinth seals were simulated in the numerical model. The task was to determine the optimal settings for high-quality modeling of the low-flow stages. The intergrid interface application issues, turbulence and roughness models are considered. The obtained numerical model settings are used to validate seven model stages for the range of the optimal conditional flow coefficient with Φopt = 0.008–0.018 and the conditional Mach number Mu = 0.785–0.804. The simulation results are compared with the experimental data. The high pressure stage-7 (HPS-7) stage with Φopt = 0.010 and Mu = 0.60 at different inlet pressure of 4, 10 and 40 atm is considered separately. Acceptable validation results are obtained with the recommended numerical model settings; the modeling uncertainty for the polytropic pressure coefficient δη*pol < 4% for the efficiency coefficient δη*pol exceeds the limit of 4% only in the two most low-flow stages, U and V.

Influence of Texture Portion and Dimple Area Density on the Tribological Characteristics of Dimple Textured Hydrodynamic Journal Bearing

There is a growing interest towards the textured bearings. The normal surface texture has the shape of micro-dimples with preselected diameter, area density and depth. The use of different amount of texturing and dimple area density, can be an effective way to improve tribological properties of textured bearing. In the present study, the tribological properties, of the dimple textured journal bearing of L/D = 2, such as attitude angle, load carrying capacity, friction variable and flow coefficient are estimated for different texture portion and dimple area density. The computationally efficient Progressive mesh densification method is implemented for the numerical solution. The governing Reynolds equation is discretized with the finite difference scheme and then solved using Gauss Seidel method coupled with Successive over relaxation scheme. The numerical results show that the flow coefficient and attitude angle has been improved significantly with texture portion variation. Similarly, when the dimple area density is varied, there is significant improvement in flow coefficient and attitude angle resulting in the maximum flow coefficient at the dimple area density of 0.25 and minimum attitude angle, at the eccentricity ratios from 0.5 to 0.7, for the dimple area density of 0.20. However, the texture portion and dimple area density have no positive influence on the load carrying capacity and friction variable.

Regional Physiographic Study for the Hydrology of Kali Lamong Watershed Area

This study aims to determine the effect of physiography based on slope and land cover for water control in Kali Lamong watershed. The data used in this research are DEM data and Landsat 8 imagery data. The process of processing slope data is through conversion coordinates system, DEM clip, create slope, reclassify, dissolve shapefile, and slope classification analysis. Landsat 8 data processing goes through a process through conversion coordinates system, composite band, crop composite, extent shapefile, sharpen band, unsupervised classification, and land cover classification analysis. Slope classification maps and land cover classification maps are used for flow coefficient classification for physiographic analysis based on slope and land cover for water control in Kali Lamong watershed. On the land cover classification map, five land classifications were obtained, namely agriculture (158413000 m2), settlements (72701400 m2), industrial land (11571600 m2), plantations (46017800 m2), and waters (15268500 m2). On the slope classification map obtained 5 classifications, as flat with a slope of 0-8% (288469544 m2), as slope with a slope of 8-15% (7656738 m2), as rather steep with a slope of 15-25% (1905360 m2), as steep with a slope of 25-45 (526614 m2), and as very steep with a slope of more than 45% (32148 m2). From the combination of Landsat 8 image data and slope data, flow coefficient analysis was carried out. The flow coefficient is influenced by land cover and slope. From this research, the classification of low flow coefficient is less than 0.25, medium flow coefficient is 0.25-0.5, and high flow coefficient is more than 0.75. The average flow coefficient of Kali Lamong watershed is 0.49 with a moderate flow coefficient classification value. This shows that 49% of the runoff water is in Kali Lamong watershed. The higher the flow coefficient value, the water runs off the surface. So that it can be used as an initial study for the technical planning of Kali Lamong hydrology and the development, improvement, utilization, and control of water flow in Kali Lamong.

Experimental Research on the Measurement of High-Pressure Microflow Based on Momentum Principle

The fuel injector is an important component of the diesel engine. It has a great influence on the atomization of diesel fuel injection, the formation of mixed gas, and combustion emissions. Due to the current nozzle structure, processing level, and the internal hydraulic conditions of each nozzle, there are certain differences between the injection rules of each hole, and there are few methods to quantify the quality of the injector using mathematical methods in engineering. Based on the principle of spray momentum, this paper measures the injection characteristics of each hole of four five-hole pressureless chamber injectors of the same model and analyzes the circulating fuel injection volume and flow coefficient of each injector and each hole under different working conditions. It is proposed to evaluate the quality of the injector with the average circulating fuel injection volume, average flow coefficient, and nonuniformity as indicators. The test results are as follows: there are differences in the circulating fuel injection volume and flow coefficient between each hole of the same fuel injector. With the increase of the fuel injection pump speed, the average circulating fuel injection volume of each hole differs by 2.8%–47.5%, and the average flow coefficient differs by 3.7%–30%; as the fuel injection volume increases, the average circulating fuel injection volume of each injector differs 1.8%–36%, and the average flow coefficient difference is 2.5%–28.7%. The circulating fuel injection volume and flow coefficient of different fuel injectors of the same model are different. With the increase of the fuel injection pump speed, the average circulating fuel injection volume of each injector differs by 3.5%–9.6%, and the average flow coefficient differs by 1.4%–5.7%; as the fuel injection volume increases, the average circulating fuel injection volume of each injector differs 0.3%–5.5%, and the average flow coefficient difference is 2.8–4.2%. The relative flow coefficient of each hole differs from 0 to 0.02, and the nonuniformity differs from 1.8% to 16.9%. The relative circulating fuel injection amount of each hole differs from 0.02 to 0.1, and the nonuniformity differs from 1.1% to 6.9%. The relative flow coefficient of each hole and its nonuniformity is smaller than the relative circulating fuel injection volume of each hole and its nonuniformity.

Research on the Percolation Mechanism of Perturbation Under Simultaneous Fracturing in Shale Reservoirs

Compared with conventional reservoirs, shale gas reservoirs usually have no natural productivity or lower productivity, and the rate of production decline is high in the later stage. The production of shale gas can be effectively improved by designing reasonably or fracturing. Therefore, it is critical for shale gas reservoir to study how to design proper parameters to make it effectively developed. Based on data of block-A region of the Zhejiang gas field, considering the contribution of rock compression to the production, the productivity formula of horizontal well at different seepage stages is deduced. Data from block-A are verified by orthogonal experiment, including gas reservoir parameters and engineering parameters. The results show that the order of reservoir parameters that affect the development of shale gas is as follows: Langmuir pressure, diffusion coefficient, cross flow coefficient, and Langmuir volume; the order of engineering parameters that affect the development of shale gas is as follows: number of fractures, horizontal section length, production pressure, fractures length, row spacing, and well spacing. The research results have been applied to the Zhejiang gas field. The initial rate of decline after adjustment is reduced by 26.08% and production increases by 17.06% after stabilization compared to wells without adjustment parameters. The research has important reference significance for the efficient development of similar gas reservoirs.

Scaling behaviors of heavy flavor meson suppression and flow in different nuclear collision systems at the LHC

We explore the system size dependence of heavy-quark-QGP interaction by studying the heavy flavor meson suppression and elliptic flow in Pb–Pb, Xe–Xe, Ar–Ar and O–O collisions at the LHC. The space-time evolution of the QGP is simulated using a $$(3+1)$$ ( 3 + 1 ) -dimensional viscous hydrodynamic model, while the heavy-quark-QGP interaction is described by an improved Langevin approach that includes both collisional and radiative energy loss inside a thermal medium. Within this framework, we provides a reasonable description of the D meson suppression and flow coefficients in Pb–Pb collisions, as well as predictions for both D and B meson observables in other collision systems yet to be measured. We find a clear hierarchy for the heavy meson suppression with respect to the size of the colliding nuclei, while their elliptic flow coefficient relies on both the system size and the geometric anisotropy of the QGP. Sizable suppression and flow are predicted for both D and B mesons in O–O collisions, which serve as a crucial bridge of jet quenching between large and small collision systems. Scaling behaviors between different collision systems are shown for heavy meson suppression factor and the bulk-eccentricity-rescaled heavy meson elliptic flow as functions of the number of participant nucleons in heavy-ion collisions.

Evaluation on biophysical carrying capacity to support land rehabilitation planning in the upstream watershed

A comprehensive Soil and Water Conservation (SWC) plan is needed, supported by information on the condition of the Biophysical Carrying Capacity (BCC) of the watershed so that land rehabilitation activities will be right on target. The research aims to evaluate the BCC to support the SWC planning for the upstream watershed. The research area was in the Naruan Micro Watershed (NMW), the upstream of Keduang Sub Watershed, the Bengawan Solo Watershed. The analysis of the BCC used evaluation criteria based on the Ministry of Forestry Regulation (PerMenhut) No. P.61/Menhut-II/2014 concerning monitoring and evaluation of watershed management. The evaluation showed that the BCC in the research area was in the “Bad” category with a value of 128.0. It means that the watershed needs to be restored, particularly in terms of biophysical features. Several parameters indicated a poor category, i.g. the land aspect such as Percentage of Degraded Land (PDL) and Erosion Index (EI) parameters, while in the water system aspect such as the Flow Regime Coefficient (FRC), Annual Flow Coefficient (AFC), and Sediment Load (SL) parameters. These five parameters must become a concern and an important starting point for land rehabilitation planning in the form of SWC measures.

Analysis of water condition in Dodokan watershed, Lombok, Indonesia

Watershed of Dodokan in Lombok, Indonesia, is one of the strategic watersheds on the island of Lombok, and is a priority for rehabilitation of forest and land. This paper aims to analyse ecological water conditions in Dodokan watershed, Lombok, Indonesia, and recommends policy for improving the ecological conditions of the watershed. The results of this analysis are expected to be useful in implementing policies and programs to improve the ecological condition of this watershed, as well as to provide greater benefits for the communities around or related to this watershed. The watershed analysis focuses on five aspects, including flow regime coefficient, annual flow coefficient, sediment load, flood, and water use index. The results of the analysis show that the ecological condition of water management in the Dodokan watershed is poor, and can threaten the continuity of water resources in the Dodokan watershed. Therefore, rehabilitation activities are urgently needed.