Compressor deep surges are observed to be of either near-resonant type or convective type. The differences of the behaviors and the boundaries between both types were tried to make clear in the situations of a single-stage axial compressor on the basis of numerical-experimental results by use of a surge simulation code. In the near-resonant surges, the surge frequencies relative to the resonance frequency range roughly from 0.9 to 1.1, close to the resonance condition. The surges tend to degenerate just above or in the resonance range. The convective type is said to perform actions of emptying and filling the flow in the delivery plenum, showing lower relative surge frequencies less than 0.9. The study for the criteria governing the boundary between both surge types has suggested an axial motion parameter as the candidate. The convective surges are observed to occur above the boundary value of the axial motion parameter. In the environment, the fluctuation amplitudes tend to be larger than those in the near-resonant surges. The situations force the compressor to work over a wider range from the turbine-action zone to the deeply-reverse flow zone along the stage characteristic. The flow reversals thus reinforced will enhance the so-called emptying and filling actions in the convective surges.

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Drilling sampling technology is an important means for obtaining underground physical data and evaluating mineral reserves. The coring diamond bit is located in the front of the drilling equipment, which can reflect the drilling efficiency and core recovery of the bit when drilling into the coring. In order to improve the drilling efficiency and core recovery, a design scheme of diamond bit for seafloor drills is proposed, which combines the formation characteristics of the seafloor within 300 meters. Based on the fluid dynamics theory and considering the effect of bit rotation on the flow field at the hole-bottom, the effects of bit water passage structure and drilling parameters on the flow field are analyzed. The results show that the designed bit can avoid the core erosion by 80% of the drilling fluid. The rotary speed should be controlled at 250 - 330 rpm, and the pump displacement should be 50 - 60 L/min. When the drilling fluid is up-return along the hole wall, the velocity first rises and then drops, then stabilizes between 0.8 - 1.3 m/s, which meets the range requirements for the standard cuttings up-return and the stability of the hole wall. Finally, the rationality of the bit design scheme is verified by field drilling experiments. The average core recovery percent reaches 85 %, which is about 25% higher than the conventional bit of water passage system.

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High-pressure-ratio multi-stage axial flow compressors tend to show complicated behaviors of frequencies in deep surges, including discontinuous changes. The phenomena for a nine-stage compressor were investigated by one-dimensional numerical simulations. The phenomena were found to occur somewhere in the range of roughly (90 – 100)% of the design speed, where incomplete surge recoveries, i.e., premature surge recoveries accompanied by immediate re-stallings, tend to occur, resulting in longer surge periods and lower surge frequencies. The incomplete surge recoveries are found to occur by premature unstalling owing to re-ingestions of the reversed hot air produced by the preceding surge, which is too hot for the compressor to work normally. The re-ingestion temperature, and the duration time of the hot re-ingestion relative to the normal suction appear to affect significantly the recovery process. It tends to occur essentially in the range of (90 -100)% of the design speed, where the compressor working conditions are changeable sensitively to small changes in the working conditions. The situations are found to be governed mainly by the following parameters; the representative tip Mach number, the reduced resonance frequency related with the suction flowpath, and the relative location of the compressor in the whole flowpath. Sufficiently below and above the sensitive speed range, the situations keep their respective stable and continuous surge behaviors. In the higher speed range, the deep surges having lowered frequencies at higher speeds become the normal state. The phenomena depend strongly on the design conditions, i.e., speed and pressure ratio and number of stages. The above conclusions suggest the natures of the discontinuous frequency behaviors in high-pressure-ratio multi-stage compressors, although they are qualitative in that they are strongly influenced by the present particular design conditions and the accuracies of the employed analysis.

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Guide vanes are a mechanical system used to direct flow in the desired direction. At lower operating conditions, implementing a guide vane system in the draft tube of a hydro-turbine can decrease the excess swirl in the flow and, thus, reduce pressure fluctuations. The present study discusses a numerical methodology to design an effective guide vane system in the draft tube of a high head Francis model turbine. The numerical method is computationally efficient and thus, saves excess computational time and data storage required for parametric analysis of the guide vane system. The aim is to mitigate the ‘rotating’ vortex rope with minimum additional losses in the turbine. The factors considered for the guide vane system design are a) number of guide vanes, b) chord length, c) span, d) inlet-outlet angles of the guide vanes, and e) their position in the draft tube. The parametric study comprises a) ideal guide vane design and b) realistic guide vane design study. The ideal guide vane design study was with the standalone draft tube domain. The realistic guide vane design study used the passage domains of the distributor, runner, and complete draft tube. From the ideal guide vane design study, a guide vane system with two or three guide vanes of chord 86% of runner radius and leading-edge span of 30% of runner radius effectively mitigates the rotating vortex rope. The system with three guide vanes is the most efficient when placed at some distance below the runner exit with mitigation above 95%

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Aiming at the problem that it is difficult to accurately predict the flexible operation conditions and state trend of hydraulic turbine, in this paper a cascade model of BP-LSTM classification prediction is proposed, which can identify the working conditions of existing fusion data, and then predict the measuring points of different working conditions. Based on the pressure parameters of hydraulic turbine units, the improved BP neural network is used to determine the operation conditions of hydraulic turbine units, and the classified data is redivided to establish the multivariate LSTM prediction model. By optimizing the parameters of the multivariate LSTM prediction model, such as the structure, the number of network layers and the number of hidden layer neurons, finally established the cascade model of BP-LSTM classification prediction of time series of hydraulic turbine units. Through experimental verification and analysis, BP-LSTM classification prediction model can predict the operation trend of measuring points under different working conditions after classification. Compared with other models, BP-LSTM model has higher prediction accuracy and better effect. The cascade model of BP-LSTM classification prediction of time series provides a model basis for the research of predictive control of hydraulic turbine units.

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The variation of coasting-down hydrodynamic characteristics of the sodium pump in the primary circuit of fast reactor is related to the safe and stable operation of nuclear power plant. In order to explore the variation rule of performance parameters during the coasting-down process, the prototype of the sodium pump (Vertical double suction coaxial in and out submersible pump) in the primary circuit of fast reactor was taken as the research object in this paper. Based on the N-S equation and the RNG k-ε turbulence model, the Fluent software was used. The UDF function was written to carry out unsteady numerical calculation on the coasting-down process of sodium pump, and the variation rule of rotating speed, flow rate, head, torque and pressure with time in the coasting-down process was obtained. The results show that during the coasting-down process，the time for the model pump rotating speed to drop to half (296.5 r/min) is more than 15 s, and the time to drop to the minimum (112 r/min) is more than 74 s, which meets the nuclear safety standards. The flow rate ratio and the rotating speed ratio have the same change law, the head ratio and the torque ratio have the same change law, and the decline speed of the head ratio and torque ratio is greater than the rotating speed ratio and the flow rate ratio, which conforms to the similarity law of the pump. During the coasting-down process, the energy of the model pump pressure pulsation is mainly concentrated at middle and low frequencies. With the increase of the coasting-down time, the amplitude of pressure pulsation decreases gradually, and the uniformity of pressure distribution at circumferential direction decreases gradually. In addition, under the influence of pressure pulsation and the complexity of flow passage of the flow components, the head has a pulsating downward trend.

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This paper presents the effort on big fan efficiency enhancement by the modification of impeller geometry especially blades angles and radius while maintaining the other parameters such as casing geometry, entry and exit diameters, rotational speed, number of blades, flow rate, and static pressure matching to the field requirement including existing installation. The combination of numerical calculation based on the semi-empiric formulas and computational fluid dynamics (CFD) is used as the methodology. Two big fans, A and B, which are widely used in the cement industry with nominal flow capacities of 300,000 and 567,500 m3/h and having static pressures of 4,000 and 12,200 Pa, were used as case studies. Theoretical performance comparison between original and modified fan design geometries as well as field measurements were also conducted in this study. The results show that modified geometry design can increase up to 4.53% of fan efficiency which contribute to reduce shaft absorbed power up to 50 kW for fan A and 130 kW for fan B respectively.

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The axial flow hydraulic turbine with a collection device can be simply installed in the flowing water of an open channel with shallow water depth to generate electricity, and the power output is increased by collecting and increasing the velocity of the flow. When the power output of this hydraulic turbine is insufficient, it is necessary to install several turbines in series with the flow in narrow channels, and it is necessary to establish a guideline for appropriate installation intervals. In this study, the relationship between the velocity distribution and the vortex structure inside and outside the hydraulic turbine was investigated by experiments and multiphase flow analysis considering free surface in order to clarify the slipstream characteristics of this hydraulic turbine in an open channel with shallow water depth. As a result, it was clarified that the axial flow velocity behind the brim recovered rapidly due to the momentum exchange between the flow passing through the outside of the hydraulic turbine and the flow passing through the inside of the hydraulic turbine. It was also discovered that all the major vortices disappeared at a position 9 times the runner diameter in the downstream direction from the runner center, and more than 70% of the axial flow velocity was recovered in the entire width direction.

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Cooling designs inside the gas turbine blades of aircraft engines are aimed to solve a problem that has existed since the very beginning of the aerospace industry. Since the working environment of turbine blades is extremely harsh when the temperature can rise to 2000K, which is considered a huge challenge for any materials. Therefore, cooling designs such as rib turbulators have always been researched and optimized for better heat transfer enhancement in the cooling mechanism of turbine blades. In this study, a geometric optimization of the rib turbulators inside a rectangular channel was performed with the aim to maximize heat transfer performance. This study investigated the effect of four rib configurations on the heat transfer efficiency of the channel, which include square, truncated-root, convergent truncated-root, and divergent truncated-root rib. Thereby, a module of coupling Python and OpenFOAM was developed to automatically perform the optimization of truncated-root rib design at Reynolds number of 37,000 with design variables are the upstream and downstream height with Powell optimization method. The aim is to figure out the point where the maximum heat transfer performance of the channel is achieved. The study presented in a specific, productive, and accurate way the factors that directly and indirectly affect the heat transfer performance of the channel, thereby giving the optimal results that the channel has the highest heat transfer performance of the presented designs. The results show that the highest heat transfer performance of the optimized design is 12.45% higher than the standard square ribs case.

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The centrifugal pump is an important rotating machine and it is very critical to identify and differentiate among its common faults as quickly and accurately as possible. Based on the ReliefF algorithm and the sparrow search algorithm (SSA) in conjunction with support vector machine (SVM), an approach for faults classification and diagnosis of centrifugal pumps is proposed, its advantages over traditional fault diagnosis methods include a reduction in the number of characteristic parameters, shorter diagnosis times, as well as improved classification accuracy and robustness. We collected the fault data by designing a centrifugal pump fault test bench that recorded vibration signals for the rotor misalignment fault, the rotor unbalance fault, the seal ring wear fault, and normal operating conditions, and preprocessed the collected signals with Kalman filtering to remove noise interference, the time domain characteristic indexes and the frequency domain characteristic indexes of the filtered signal were extracted, each feature index is given a distinct weight using the ReliefF method, and the eigenvalues with weights less than the threshold are deleted, and the feature indexes that remain create a defect feature matrix. Particle swarm optimization (PSO), genetic algorithm (GA), and simulated annealing algorithm (SA) were used to optimize the SVM for comparison in order to verify the SSA-SVM model's performance for fault diagnosis. The comparison results show that the model has high recognition accuracy, short Classification time, and strong robustness.

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