Estimation of Turbulent Length Scales at a Turbocharger Inlet using Stereoscopic Particle Image Velocimetry

Stereoscopic Particle Image Velocimetry measurements are carried out at the inlet of a turbocharger compressor at four different shaft speeds from 80,000 rpm to 140,000 rpm and over the entire range of flow rates from choke to mild surge. This paper describes the procedure used in processing the PIV data leading to the estimates of turbulent length scales - integral, Taylor, and Kolmogorov, to enhance the fundamental understanding and characterization of the compressor inlet flow field. The analysis reveals that at most operating conditions the three different length scales have markedly different magnitudes, as expected, while they have somewhat similar qualitative distributions with respect to the duct radius. For example, at 80,000 rpm and at a flow rate of 15.7 g/s (mild surge), the longitudinal integral length scale is of the order of 15 mm, the Taylor scale is around 0.5 mm, and the Kolmogorov scale is about 10 microns. With the onset of flow reversal, the turbulent kinetic energy and turbulent intensity at the compressor inlet are observed to increase rapidly, while the magnitudes of the Kolmogorov scale and to a certain extent, the Taylor scale are found to decrease suggesting that the increased turbulence gives rise to even smaller flow structures. The variation of length scales with compressor shaft speed has also been studied.

THE EFFECT OF BEND ANGLE ON THE EVAPORATIVE COOLING OF AIR FLOW THROUGH BENT DUCT

One remediation to output power drop of a gas turbine generating units during hot climates is reducing compressor inlet air temperature using fogging technique incorporating water injection into the airstream. The inlet air ductworks often include a bend or curved duct before the compressor comprising the secondary flow utilized to enhance the mixing between air and water droplets. This study investigates the effect of changing the bend angle on the resultant evaporative cooling of steadily flowing airstream. The experiments were conducted with an average air velocity range from (2.5 to 5 m/s) through (50) cm square duct. The study considered three bend angles of (45°, 90° and 135°) along with three sets of nozzle tilt angles of (- 45o, 0° and 45° ) to the axial flow direction. The results reveal that best evaporative cooling was achieved at a bend angle of (135°) when the water is axially injected, i.e., at (0o) to flow direction. These conditions were obtained at the velocity of (2.5 m/s), giving enough residence time for the injected droplets to evaporate and cool the airstream.

Optimizing Gas Production from Giant Multi-Reservoir Onshore Abu Dhabi Gas Field by Introducing Wellhead Compressors and Reconfiguring the Surface Network Using an Integrated Asset Model IAM

The giant onshore gas field in this study consists of six stacked reservoirs and has been producing for over three decades. The field has more than 150 gas producing wells and has several wells which have low-intermittent gas production rates. The low production is attributed to weak wells sharing common trunk lines with prolific wells. This study investigates the impact of choke optimization, surface network reconfiguration and wellhead compression to improve the gas production from weak wells after performing detailed analysis of possible root causes from the surface network by using an Integrated Asset Model (IAM) as the digital twin of the field. The investigation begins by identifying weak producers and involves studying the integrated surface network and determining the root causes for backflow and unstable hydraulics. After surface network issues have been recognized, remedial modification will be implemented. The impact of different choke settings on the wells are studied. The final step will be to introduce wellhead compressors on the weak producers. Extensive sensitivity scenarios are performed to identify the optimum compressor inlet pressure for each individual wellhead compressors and the wells which benefit most from the application of wellhead compressors are ranked. The multi-reservoir gas field contains six stacked reservoirs which are producing under depletion mode and share a common surface network. Root causes of weak or shut-in wells due to backflow or hydraulic issues are successfully identified by using an IAM simulation tool. The investigated remediations were simple optimization of the choke settings, reconfiguration of the surface network, and application of wellhead compressors to improve the gas production from the problematic wells. It is observed that the addition of wellhead compressors resulted in the most significant increase and more sustainable production from the weaker wells. Furthermore, the final selection of candidate wells for wellhead compressors can be dictated according to the highest gain from the ranking. The study revealed that the implementation of wellhead compressors will significantly increase the cumulative gas production from the selected wells at the end of field life and will result in positive production acceleration from the field perspective. This study shows that adding wellhead compressors to weak producers can mitigate the production bottlenecks and backflow issues and that higher and more sustainable gas production can be achieved from the weak wells after understanding the primary causes for low/intermittent production from the IAM which is acting as the digital twin of the field.

Research on Response Characteristics and Control Strategy of the Supercritical Carbon Dioxide Power Cycle

With the development of GEN-IV nuclear reactor technology, the supercritical carbon dioxide (SCO2) Brayton cycle has attracted wide attention for its simple structure and high efficiency. Correspondingly, a series of research has been carried out to study the characteristics of the cycle. The control flexibility of the power generation system has rarely been studied. This paper carried out a dynamic performance of the 20 MW-SCO2 recompression cycle based on the Simulink software. In the simulation, the response characteristics of the system main parameters under the disturbances of cooling water temperature, split ratio, main compressor inlet temperature and pressure were analyzed. The results show that the turbine inlet temperature is most affected by the disturbances, with a re-stabilization time of 2500–3000 s. According to the response characteristics of the system after being disturbed, this study proposed a stable operation control scheme. The scheme is coordinated with the main compressor inlet temperature and pressure control, recompressor outlet pressure control, turbine inlet temperature control and turbine load control. Finally, the control strategy is verified with the disturbance of reduced split ratio, and the results show that the control effect is good.

Investigation of variable geometry orifice design for improving centrifugal compressor low-end performance and stable operating range

Active control of the inlet flow area in a centrifugal compressor is a method to improve compressor aerodynamic performance and stall margin. As a core part of the area control device, the variable geometry orifice is investigated and its two key design parameters are analyzed in detail, the setting angle of the orifice with respect to the shroud casing and the radial height of the orifice to the shroud casing from the orifice inner rim. This paper proposes a physics-based equation that describes the relationship of the two parameters with compressor mass flow rate and then validates the equation using numerical simulations. As far as the setting angle, the physics-based equation suggests not to be larger than 90°. The numerical results not only validate the physics-based equation but also show the most optimal angle of 78°. In terms of the orifice height, both the physics-based equation and the numerical simulations suggest an active height control of orifice in the compressor inlet duct.

Accommodation of Multi-Shaft Gas Turbine Switching Control Gain Tuning Problem to IGV Position

This article aims to discuss the influence of compressor Inlet Guide Vane (IGV) position on gas turbine switching control system gain tuning problem. The distinction between IGV and normally reckoned working conditions is differentiated, and an improved double-layer LPV model is proposed to estimate the protected parameters under various IGV positions. Controller gain tuning is conducted with single and multi-objective intellectual optimization algorithms. Simulation results reveal that normally used multi-objective optimization procedure is unnecessary and time-consuming. While with the comprehensive indicator introduced in this paper, the calculation burden can be greatly eased. This improvement is especially advantageous when tuning work is carried out under multiple IGV positions.

Компактный аппаратно-программный комплекс для диагностики электронных регуляторов САУ ГТД в эксплуатации

The relevance of creating a compact hardware and software complex is analyzed to ensure a full check of the operability of electronic regulators of gas turbine engines, in particular, the AI-35 engine, developed by SE "Ivchenko-Progress". The article describes the composition and functionality of the device developed by Element JSC, which was named “Complex of software and hardware for imitation of actuators and engine sensors”. The complex under consideration is intended both for autonomous use and for work as part of an automated workstation (AWS), which in turn is a part of the AI-35 engine semi-natural simulation stand. A feature of the complex is that it contains built-in mathematical models of the engine, electric drive pump-fuel regulator, as well as sensors installed on the engine. Based on the results of processing digital signals from an automated workstation or a touchscreen display, the complex generates output analog and frequency signals – rotor speed, pressure at the compressor outlet, the temperature at the compressor inlet, temperature of gases at the outlet of the turbine. The complex also generates control signals for the imitation of igniting pyro plugs and a fuel pyrovalve, in particular, it provides an imitation of their "combustion" by breaking the circuit. The built-in touchscreen display makes it easy for the operator conducting the governor and engine tests to use the complex as intended. With the help of the display, without using a PC, the operator can manually control the process of simulating the issuance of a command to start the engine by changing the values of the rotor speed, form various modes of engine operation, setting the appropriate parameters, simulate engine surge, etc. The functionality of the developed complex provides debugging of GTE control algorithms and subsequent tests of the regulator.

Impact of volumetric system design on compressor inlet conditions in supercritical CO2 cycles

The paper aims to improve the understanding of the dependency of compressor inlet conditions close to the critical point in supercritical CO₂ (sCO₂) cycles on different volumetric cycle designs. The compressor inlet conditions are fixed by the specific static outlet enthalpy of the main cooler and the static pressure determined by the mass of CO₂ in the closed cycle. While in a previous study the authors analyzed effects on the compressor inlet conditions with respect to the specific static enthalpy in the pseudocritical region for constant inlet pressure, this paper focuses on the influence of the volume of the heater and cooler. The analysis is based on experimental observations from two different experimental sCO₂ cycles, the SUSEN loop and the HeRo loop. The change of compressor inlet pressure upon change of the cooling power is substantially different and caused by the different volumetric design of the cycles. A simple model based on the volumes of the hot and cold sections in the cycle is developed to understand the dependency of compressor inlet conditions on the volumetric design. In terms of the volumetric design of the cycle, the paper will improve the knowledge of the challenges in stable compressor operation close to the critical point.

Surge Prevention Techniques for a Turbocharged Solid Oxide Fuel Cell Hybrid System

Pressurized solid oxide fuel cell systems are one of the most promising technologies to achieve high efficiencies and reduce pollutant emissions. This study focuses on an innovative layout, based on an automotive turbocharger, which improves cost effectiveness at small size (<100 kW), despite reducing slightly the efficiency compared to micro gas turbines based layouts. This turbocharged system poses two main challenges. On one side, the absence of an electrical generator does not allow the direct control of the rotational speed. On the other side, the large volume of the fuel cell stack between compressor and turbine alters the dynamic behavior of the turbocharger during transients, increasing the risk of compressor surge. The pressure oscillations associated with surge are particularly detrimental for the system and could damage the materials of the fuel cells. The aim of this paper is to investigate different techniques to drive the operative point of the compressor far from the surge condition when needed, increasing its reliability. Using a system dynamic model, developed with the TRANSEO tool by TPG, the effect of different anti-surge solutions is simulated: (i) water spray at compressor inlet, (ii) compressor fogging, (iii) air bleed, (iv) recirculation and (iv) ejector-aided recirculation at compressor intake. The system is simulated with two different control strategies, i.e. constant fuel mass flow and constant turbine inlet temperature. Different solutions are evaluated based on surge margin behavior, both in the short and long terms, but also monitoring other relevant physical quantities of the system.