Variable Guide Vanes Research Articles

Numerical Investigation and Optimization of Variable Guide Vanes Adjustment in a Transonic Compressor

In the present work, numerical simulation and optimization was carried out to analyze the mechanism of the variable guide vanes (VGVs) of a transonic compressor. A seven-stage transonic compressor including three-stage VGVs was studied. The VGVs were adjusted individually and jointly under different IGV opening degrees. Changes in performance and shock wave were analyzed, and the coupling effect of the VGV joint adjustment was summarized. Aiming at the maximum efficiency, the joint turning angles were optimized. A novel phenomenon was found wherein the VGV adjustment can affect not only its own performance and that of adjacent downstream blades, but also that of upstream blades. Incidence and performance of upstream blades are improved, but those of the VGV and its adjacent downstream blades are deteriorated. VGV adjustment weakens the shock wave and shock-induced boundary layer separation. The optimal solution for VGV joint adjustment is the combination of the optimal solutions for single VGV adjustments. The joint adjustment optimization improves the efficiency by 0.2–1.93% under different IGV opening degrees.

Variable Guide Vane Scheduling Method Based on the Kinematic Model and Dual Schedule Curves

The variable guide vanes (VGV) of gas turbine engines are commonly utilized to expand operating range and to improve efficiency of the compressor. Guiding air flow using the VGVs in the compressor prevents aerodynamic instability by making proper incidence angle to the blades. In this study, we dealt with rig-type three-stages VGVs for developed engine tests. The three link mechanism of VGVs are linked to each other with two hydraulic actuators, and inevitably, induced hysteresis exists between vane rotations and actuators strokes, due to links with non-fully constrained degree of freedoms for easy installation and instrumentation, as well. Therefore, the adjustment of each VGVs link mechanism is required to satisfy vane angle demands. To adjust coupled three-stages VGVs link mechanism, an analytical VGV-link kinematic model was derived, and effects of two adjusting parameters (lengths of bell cranks and vertical links) were discovered. Lastly, we obtained two vane angle schedule curves from the experiments according to link moving directions, and applied them to the engine controller to minimize hysteresis of the variable inlet guide vane (VIGV). The proposed VGV adjusting and controlling method can be simply applied to the pre-designed or pre-manufactured VGVs system without mechanical compensation or additional cost.

Off-design heating/power flexibility for steam injected gas turbine based CCHP considering variable geometry operation

Owing to the fluctuating energy demand from consumer side, combined cooling, heating and power (CCHP) system operates at off-design condition most of the time. Moreover, the heating/power surplus is a common problem for the conventional CCHP system. In order to improve the precision of performance prediction and partly relieve the heating surplus, a steam injected gas turbine (STIG) based CCHP system considering off-design condition is proposed. The system consists of a steam injected gas turbine, double-pressure heat recovery steam generator (HRSG), heat exchanger, absorption chiller and auxiliary boiler. Two different operation strategies including turbine inlet temperature (TIT) strategy and variable guide vanes (VGVs) strategy, are illustrated to access the part-load performance of gas turbine and CCHP system. The performance indicators, like primary energy saving rate (PESR), primary energy rate (PER) are set up to evaluate the thermodynamic performance of the CCHP system. A simple gas turbine (SGT) based CCHP is chosen as the comparative object and two energy demand cases are selected to validate the advancement. The results show that VGVs strategy does not improve the gas turbine efficiency significantly but bring more exhaust heat into HRSG. VGVs strategy advances the heating to power ratio, PESR and PER around the whole part load condition, i.e., PESR is elevated from 0.3254 to 0.3743 by VGVs at the half of gas turbine load without injected steam. Injecting steam is a more effective way to improve gas turbine efficiency rather than using VGVs strategy while implementing same gas turbine load. Steam injection does not always enhance the PESR, but the PER keeps decreasing as injected steam flow increases around the whole load. STIG based CCHP system with VGVs operation strategy gets the best performance among these studied approaches, and the maximum enhancement of PESR reaches 0.3171 in the proposed energy demand cases.

Combining effect of optimized axial compressor variable guide vanes and bleed air on the thermodynamic performance of aircraft engine system

Aim of this work is to provide evidence of the effectiveness of combined use of the variable guide vanes (VGVs) and bleed air on the thermodynamic performance of aircraft engine system. This paper performed the comparative study to evaluate the overall thermal performance of an aircraft engine with optimized VGVs and bleed air, separately or simultaneously. The low-bypass ratio turbofan engine has been modeled with a 0D/1D modeling approach. The genetic algorithm is employed to find the optimum schedule of VGVs and bleed air. There are four types of design variables: (1) the inlet guide vane (IGV) angle, (2) the IGV and 1st stator vane (SV) angles, (3) bleed air mass flow rate at the exit of the axial compressor, and (4) both type 2 and type 3. The optimization is conducted with surge margin constraints of more than 10% and 15% in the axial compressor. The results show that the additional use of the bleed air increases the efficiency of the compressors. Overall, the percentage reductions of the total fuel consumption for the engine with the IGV, 1st SV and bleed air schedule is 1.63% for 15% surge margin constraints when compared with the engine with the IGV schedule.

Introduction of Circumferentially Nonuniform Variable Guide Vanes in the Inlet Plenum of a Centrifugal Compressor for Minimum Losses and Flow Distortion

In the oil and gas industry, large variations in flow rates are often encountered, which require compression trains with a wide operating range. If the stable operating range at constant speed is insufficient, variable speed drivers can be used to meet the requirements. Alternatively, variable inlet guide vanes (IGVs) can be introduced into the inlet plenum to provide pre- or counterswirl to the first-stage impeller, possibly eliminating the need for variable speed. This paper presents the development and validation of circumferentially nonuniform IGVs that were specifically designed to provide maximum angle variation at minimum losses and flow distortion for the downstream impeller. This includes the comparison of three concepts: a baseline design based on circumferentially uniform and symmetric profiles, two circumferentially nonuniform concepts based on uniquely cambered airfoils at each circumferential position, and a multi-airfoil configuration consisting of a uniquely cambered fixed part and a movable part. The idea behind the circumferentially nonuniform designs was to take into account nonsymmetric flow features inside the plenum and a bias toward large preswirl angles rather than counter-swirl during practical operation. The designs were carried out by computational fluid dynamics (CFD) and first tested in a steady, full-annulus cascade in order to quantify pressure losses and flow quality at the inlet to the impeller at different IGV setting angles (ranging from −20 deg to +60 deg) and flow rates. Subsequently, the designs were mounted in front of a typical oil and gas impeller on a high-speed rotating rig in order to determine the impact of flow distortion on the impeller performance. The results show that pressure losses in the inlet plenum could be reduced by up to 40% with the circumferentially nonuniform designs over the symmetric baseline configuration. Furthermore, a significant reduction in circumferential distortion could be achieved with the circumferentially nonuniform designs. The resulting improvement in impeller performance contributed approximately 40% to the overall efficiency gains for inlet plenum and impeller combined.

A full engine cycle analysis of a turbofan engine for optimum scheduling of variable guide vanes

This paper proposes a full engine cycle analysis to derive the schedule of variable guide vanes (VGVs) in a multi-stage axial compressor for improving the performance of a turbofan engine with required surge margin. Most researchers assumed the operating line of a compressor in process of scheduling of VGVs. However, it has been known that the performance of a compressor is influenced by the angle of VGVs. As a result, the performance variation of a compressor can affect an engine. Therefore, a full engine cycle analysis is conducted to consider the effect of VGVs on a turbofan engine. The VGVs are applied to the front stages of the high pressure compressor in the low-bypass ratio turbofan engine. The compressor of the front stages is transonic three-stage axial flow compressor. The commercial engine simulation program, NPSSTM is employed to analyze the on- and off-design performance of the turbofan engine. 1D meanline analysis is used for performance prediction of a multi-stage axial flow compressor with VGVs. The engine simulation program is coupled with the compressor performance prediction tool to consider the engine performance variation with application of the VGVs. The proposed scheduling algorithm of the inlet guide vane (IGV) and stator vanes (SV) is adjusting the vanes angle to have the minimum loss incidence angle at all rotor blades and to satisfy the required surge margin at off-design condition. The result shows that the proposed algorithm can obtain the scheduling of the IGV, 1st and 2nd SVs angle with stable operation and improved specific fuel consumption of the engine.

Effect of Variable Guide Vanes and Natural Gas Hybridization for Accommodating Fluctuations in Solar Input to a Gas Turbine

In recent years, several prototype solar central receivers have been experimentally demonstrated to produce high temperature and high pressure gas capable of driving a gas turbine engine. While these prototype receivers are generally small (<1 MWth), advancements in this technology will allow for the development of solar powered gas turbine engines at a commercial level (sizes of at least several megawatts electric (MWe)). The current paper analyzes a recuperated solar powered gas turbine engine, and addresses engine considerations, such as material limitations, as well as the variable nature of solar input. In order to compensate for changes in solar input, two operational strategies are identified and analyzed. The first is hybridization, meaning the solar input is supplemented via the combustion of fossil fuels. Hybridization often allows for an increase in net power and efficiency by adding heat during periods of low solar thermal input. An alternative strategy is to make use of variable guide vanes on the compressor of the gas turbine engine, which schedule to change the air flow rate into the system. By altering the mass flow rate of air, and assuming a fixed level of heat addition, the operating temperature of the engine can be controlled to maximize power or efficiency. The paper examines how to combine hybridization with variable guide vane operation to optimize gas turbine performance over a wide range of solar thermal input, from zero solar input to solar-only operation. A large material constraint is posed by the combustor, and to address this concern two alternative strategies—one employing a bypass valve and the other a combustor modified to allow higher temperature inlet air—are presented. Combustor modifications could include new materials and/or increased cooling air. The two strategies (bypass versus no bypass) are compared on a thermodynamic basis. It is found that it is possible to operate the gas turbine across the entire range without a significant drop in performance in either design through judicious adjustment of the vanes, though both approaches yield different results for certain ranges of solar input. Finally, a yearly assessment of solar share and thermodynamic performance is presented for a 4.3 MWe gas turbine to identify the overall benefits of the operational strategies. The annualized thermodynamic performance is not appreciably different for the two strategies, so that other factors such as mechanical design, operational issues, economics, etc. must be used to decide the optimal approach.

Design methods of the ABB Alstom Power gas turbine dry low emission combustion system

This paper describes the conceptual design and aerothermal approach of the ABB ALSTOM POWER UK Limited (ABB ALSTOM POWER) dry low emission (DLE) combustion system directed towards all current and future power ranges. A set of parameters was employed as a common criterion to design the company's combustion system across the product range. The parameters made it possible to scale the combustion system to operate at any required firing temperature without the penalty of achieving the low emission targets. The logic and sensible air mass mapping and testing management based on a basic knowledge of the aerothermodynamics of the combustion system and its integral parts produced reliable operation and engine results. The combustion system aerothermodynamic design considers the constraints of maintaining combustor specifications while introducing a reliable ultra-low NO x concept with minimal structural change to engine design. Furthermore, the ignition loop, piloting and stability margins were issues continuously assessed through a defined application programme to examine their impact on engine operability at various load conditions. A main radial swirler injector is utilized for both gas and liquid to produce a fuel lean mixture for combustion at full-load operating conditions, while a pilot fuel injector guarantees a local fuel-rich zone to sustain stability at low power conditions. The carefully planned switch-over between the pilot and main swirler provides smooth operation and low emission across the load range conditions. The company combustion system relies upon the principle of aerodynamic variable mixing with a single vortex generator burner. The partial premixing process takes place at the radial inflow swirler slots before the fuel—air mixture is introduced into a prechamber and thereafter into the combustion chamber. For vane passage injection the liquid liquid fuel atomization should be at an optimum and the vane passage and prechamber length set to provide the vaporization period. The impingement cooling scheme aided by a thin layer of thermal barrier coating (TBC) achieved an excellent combustor wall temperature at all operating conditions and across the DLE engines product range. The scheme made it possible to direct a large amount of air towards the swirler to achieve the lean premix combustion. Substantial CO emission reduction at part load was achieved by variable guide vanes (VGV) modulation for the single-shaft engines. This action inhibits NO formation without slowing the CO oxidation process to a frozen condition. The variable mixing regime approach and accurate air management has demonstrated an ultra-low NO x emission of 12–15 and 32–35 ppmv (corrected to 15% O2) at the full-load condition while operating on gas and distillate-2 fuel respectively. Moreover, the system exhibited low CO and dynamics oscillation capability for both gas and liquid fuel operation. At the present time, the one-dimensional analysis has been proved to be a reliable tool for combustion system designers to produce a preliminary design configuration. The particular choice for a commercial computational fluid dynamics (CFD) code to satisfy various criteria of the swirling combusting flow is proving to be difficult due to constraints regarding slover and/or methods limitation. The results obtained from the high-pressure air facilities, engine beds and field trials represent a true technological achievement through collective engineering design efforts towards emission and pollution control for small- and medium-range gas turbine engines.