A Computer Program for Simulating Transient Behavior in Steam Turbine Stage Pressure of AHWR

The last stage blades (LSBs) of low-pressure (LP) turbine power plants have been historically specified and designed on the basis of optimization studies by matching the turbine to the condenser/cooling system for a specified unit rating. LSB sizes for U.S. nuclear applications currently range from 38 in. to 52 in. for unit ratings of 600 MWe to 1200 MWe. LP turbine arrangements usually consist of two or three double-flow sections in parallel. Last stage end loadings (last stage mass flow divided by the last stage annulus area) vary from approximately 8000lb∕hsqftto14,000lb∕hsqft, with corresponding unit loadings (electrical output in megawatts divided by last stage annulus area) of 1.1 MWe∕sqftto2.1MWe∕sqft. Several power plants have been upgrading/replacing their LP turbines. Considerations include efficiency, reliability, power uprates, operating license renewals (nuclear), aging, inspection, and maintenance. In some cases, LP turbine rotors are being replaced with new rotors, blading, and steam path. Others are replacing LP turbines with new and advanced designs incorporating improved technology, better materials, optimized steam paths, more efficient blading, longer LSB sizes, redesigned exhaust hoods, etc. Unlike the other stages in the LP turbine, the last stage performance is affected by both the upstream (load) and downstream (condenser) conditions. While the LP turbines are being upgraded or replaced, no major modifications or upgrades are being made to the condensers. To address vibration effects due to increased flows and velocities from power uprates, the condenser tubes may be staked. Circulating water pumps may or may not be upgraded depending upon the particular application. Consequently, while improvements in LP turbines lead to more efficient utilization of the available energy and higher output, the last stage performance may be out of synchronization with the existing condenser/cooling system. Undersized or oversized LSB sizes in relation to the unit rating and end loading may result in less than optimum performance depending upon the design and operating range of the condenser/cooling system. This paper examines the various factors that affect last stage performance of LP turbines. Using a case study, it discusses the relationships between the last stage, the unit rating, the end loading, and the operating range of the condenser/cooling system. It examines different last stage exhaust loss curves and provides recommendations for selection of LSB sizes for optimum performance.

The last stage blades (LSB) of low-pressure (LP) turbines power plants have been historically specified and designed on the basis of optimization studies by matching the turbine to the condenser/cooling system for a specified unit rating. LSB sizes for U.S. nuclear applications currently range from 38” to 52” for unit ratings of 600 Mwe to 1200 Mwe. LP turbine arrangements usually consist of two or three double-flow sections in parallel. Last stage end loadings (last stage mass flow divided by the last stage annulus area) vary from approximately 8,000 lb/hr-sq.ft to 14,000 lb/hr-sq.ft, with corresponding unit loadings (electrical output in megawatts divided by last stage annulus area) of 1.1 Mwe/sq.ft to 2.1 Mwe/sq.ft. Several power plants have been upgrading/replacing their LP turbines. Considerations include efficiency, reliability, power uprates, operating license renewals (nuclear), aging, inspection and, maintenance. In some cases, LP turbine rotors are being replaced with new rotors, blading and steam path. Others are replacing LP turbines with new and advanced designs incorporating improved technology, better materials, optimized steam paths, more efficient blading, longer LSB sizes, redesigned exhaust hoods, etc. Unlike the other stages in the LP turbine, the last stage performance is affected by both the upstream (load) and downstream (condenser) conditions. While the LP turbines are being upgraded or replaced, no major modifications or upgrades are being made to the condensers. To address vibration effects due to increased flows and velocities from power uprates, the condenser tubes may be staked. Circulating water pumps may or may not be upgraded depending upon the particular application. Consequently, while improvements in LP turbines lead to more efficient utilization of the available energy and higher output, the last stage performance may be out of synch with the existing condenser/cooling system. Undersized or oversized LSB sizes in relation to the unit rating and end loading may result in less than optimum performance depending upon the design and operating range of the condenser/cooling system. This paper examines the various factors that affect last stage performance of LP turbines. Using a case study, it discusses the relationships between the last stage, the unit rating, the end loading and, the operating range of the condenser/cooling system. It examines different last stage exhaust loss curves and provides recommendations for selection of LSB sizes for optimum performance.

As an aircraft engine operates from sea level take-off (SLTO) to altitude cruise, the low pressure (LP) turbine Reynolds number decreases. As Reynolds number is reduced the condition of the airfoil boundary layer shifts from bypass transition to separated flow transition. This can result in a significant loss. The LP turbine performance fall-off from SLTO to altitude cruise, due to the loss increase with reduction in Reynolds number, is referred to as a lapse rate. A considerable amount of research in recent years has been focused on understanding and reducing the loss associated with the low Reynolds number operation. A recent 3-1/2 stage LP turbine design completed a component rig test program at Honeywell. The turbine rig test included Reynolds number variation from SLTO to altitude cruise conditions. While the rig test provides detailed inlet and exit condition measurements, the individual blade row effects are not available. Multi-blade row computational fluid dynamics (CFD) analysis is used to complement the rig data by providing detailed flow field information through each blade row. A multi-blade row APNASA model was developed and solutions were obtained at the SLTO and altitude cruise rig conditions. The APNASA model predicts the SLTO to altitude lapse rate within 0.2 point compared to the rig data. The global agreement verifies the modeling approach and provides a high confidence level in the blade row flow field predictions. Additional Reynolds number investigation with APNASA will provide guidance in the LP turbine Reynolds number research areas to reduce lapse rate. To accurately predict the low Reynolds number flow in the LP turbine is a challenging task for any computational fluid dynamic (CFD) code. The purpose of this study is to evaluate the capability of a CFD code, APNASA, to predict the sensitivity of the Reynolds number in LP turbines.

The vortex rope in the draft tube is considered as the major contributor to pressure pulsation at partial load (PL) conditions, which causes the hydro unit to operate unstably. Based on the prototype Francis turbine HLA551-LJ-43 in the laboratory, J-grooves are designed on its conical section in this paper. We used numerical simulation to study the effect of the J-grooves on vortex suppression and energy dissipation in the draft tube. Four typical operating conditions were chosen to analyze the vortex suppression; the corresponding flow ratios Q* are 100%, 82%, 69%, and 53%, respectively. Entropy production theory is used to calculate the energy losses and assess the effect of the J-groove on energy dissipation under part-load conditions. By comparing entropy production, circumferential and axial velocity components, swirl intensity, pressure pulsation, and vortex distribution in a draft tube with and without J-grooves at different operating conditions, it can be concluded that the entropy production on the wall containing a conical section with J-grooves is obviously smaller than that without J-grooves, the effects of J-grooves on reducing circumferential velocity component Vu, pressure pulsation, and weakening vortex intensity and vortex rope in the conical section are obvious, especially at part load and deep part-load operating conditions. Using J-grooves shows better performance on vortex control and energy dissipation in the draft tube of a Francis turbine at partial load conditions.

The objective of the present work is to establish the effect of spacer and geometrical parameters of nuclear fuel rods on the turbulent mixing rate in subchannels of the advanced heavy water reactor (AHWR) rod bundle. Experiments on the AHWR rod bundle have been carried out in a scaled test facility developed at Bhabha Atomic Research Centre, Trombay, Maharashtra. In order to confirm the validity of the proposed method, experimental data on the turbulent mixing rate were obtained using a tracer technique under adiabatic conditions with 3.5-m vertical test channels, consisting of three subchannels. The spacer was installed at 2963 mm (37 mm at the end of the mixing section), 2926 mm (74 mm at the end of the mixing section), and 2889 mm (111 mm at the end of the mixing section) from the entry section in the test section, respectively, for three different positions. The experimental results (blockage ratio 4%) have been compared with the case without spacer and finally new correlations have been developed between average mixing number, combined Reynolds number, and gap-to-centroidal ratio (S/δ). The range of average Reynolds number covered was 0 to 6424. The correlation is applicable for a vertical pressure tube–type boiling water reactor (AHWR) with a reasonable accuracy. The instrument was calibrated prior to each set of analyses with standard solution. It predicts a reasonable mixing at a higher S/δ as compared to without spacer, which is the most improved feature of the correlation when compared with the existing ones. The uncertainty analysis has been carried out for the measurement of flow rate, concentration, and height of the test section. The proposed correlation may be applicable for the thermal-hydraulic design of an AHWR with an improved accuracy. A complete set of mixing data was obtained which can be used to calibrate thermal-hydraulic codes.

Characterisation of a low pressure turbine for turbocompounding applications in a heavily downsized mild-hybrid gasoline engine

In the present work, a new technique is proposed for feedwater heating in Low Pressure (LP) turbine section of regenerative Rankine cycle. Main objective of this technique is to minimise exergy destruction in feedwater heating. The proposed technique comprised of using absorption heat boosters i.e. Absorption Heat Pump (AHP) and Absorption Heat Transformer (AHT) with LiBr–water as the working fluid. Heat booster consumes heat in the form of low quality steam from LP turbine, deliver it at better quality in absorber, and in some configuration, condenser. This heat is used for feedwater heating, which results in reduction in exergy destruction in the process. Various configurations of LP turbine section with absorption heat booster have been simulated. Results show that overall increased power output as high as 0.54% from LP turbine can be obtained. Exergy analysis of LP turbine section with heat booster shows that exergy saved through this technique get transformed into equal amount of additional power output.

Boundary layer separation and reattachment is often an unavoidable feature of low pressure (LP) turbine, one of the main causes of this phenomenon is the high altitude low Reynolds number experienced by the modern LP turbine stage in aero-engine. Although an excellent turbine airfoil design can avoid flow separation on certain extent, but within flight envelope, LP turbine’s characteristic Reynolds number may varied greatly, so it will be still under the risk of the presence of separation bubble. In this two parts paper a new concept of slotted-blade was raised to testify the gain of the blade slotting. A high aerodynamic loading LP turbine blade IET-LPTA was under investigated with different Reynolds number. Computational results reveal that the blade slotting could be a way of choice to suppress separation bubble and reduce profile loss under the condition of low Reynolds number, although its position and geometry need to be further investigated.

Simulation and thermoeconomic analysis of different configurations of gas turbine (GT)-based dual-purpose power and desalination plants (DPPDP) and hybrid plants (HP)

Technical feasibility study for coupling a desalination plant to an Advanced Heavy Water Reactor

Flow controlling of boundary layers separation of low-pressure (LP) turbine blade is still a high leverage area for advent of high lift and ultra-high lift LP turbines. At cruising conditions, the Reynolds number in the LP turbine reduces (due to the decrease in air density) to the critical value that flow starts to separate from the blade suction surface. In the present study, cascade T106A is used to control the laminar separation bubble on the suction side of the blade. Fluent® commercial CFD code with gamma theta transition model has been employed to study the boundary layer separation at various different turbulent intensities. Numerical results are validated with the available experimental data and are in good agreement. An optimize dimple is used to control the boundary layer separation at low and intermediate turbulent intensities. Normalized loss coefficient is reduced to about 5% with the help of optimal dimple size and location, which increase the LP turbine efficiency. C p plots and boundary layers profiles are made for flow visualization.

In this work, the effects of Turbine Center Frame (TCF) wakes on the aeromechanical behavior of the downstream Low Pressure Turbine (LPT) blades are numerically investigated and compared with experimental data. A small industrial gas turbine has been selected as a test case, composed of a TCF followed by the two low pressure stages and a Turbine Rear Frame (TRF) before the exhaust plenum. Full annulus unsteady computations of the whole low-pressure module have been performed. Two operating conditions, full (100%) and partial (50%) load, have been investigated with the aim of highlighting the impact of TCF wakes convection and diffusion through the downstream rows. Attention was paid to the harmonic content of rotors’ blades. From an aerodynamic point of view, the results show a slower decay of the wakes through the downstream rows in off-design conditions as compared to the design point. The wakes generated by the struts at partial load persist throughout the domain outlet, while they are chopped and circumferentially transported by the rotors motion. This is due to the strong incidence variation at which the TCF works, which induces the growth of wide regions of separated flow on the rear part of the struts. Nevertheless, the analysis of the rotors’ frequency spectrum reveals that moving from design to off-design conditions, the effect of the TCF does not change significantly, thanks to the filtering action of the first LPT stage movable Nozzle Guide Vane (NGV). From unsteady calculations the harmonic contribution of all turbine components has been extracted, highlighting the effect of statoric parts on the last LPT blade. Anyhow the TCF harmonic content remains the most relevant from an aeromechanic point of view as per experimental evidence, and it is considered for a Forced Response Analysis (FRA) on the last LPT blade itself. Finally, aerodynamic and aeromechanic predictions have been compared with the experimental data to validate the numerical approach. In the last part of this paper some general design solutions, that can help mitigation of the TCF wakes impact, are discussed.

Further improvement of state-of-the-art low-pressure (LP) turbines (LPTs) has become progressively more challenging. LP design is more than ever confronted to the need to further integrate complex models and to shift from single-component design to the design of the complete LPT module at once. This leads to high-dimensional design spaces and automatically challenges their applicability within an industrial context, where computing resources are limited and the cycle time is crucial. The aerodynamic design of a multistage LP turbine is discussed for a design space defined by 350 parameters. Using an online surrogate-based optimization (SBO) approach, a significant efficiency gain of almost 0.5pt has been achieved. By discussing the sampling of the design space, the quality of the surrogate models, and the application of adequate data mining capabilities to steer the optimization, it is shown that despite the high-dimensional nature of the design space, the followed approach allows to obtain performance gains beyond target. The ability to control both global as well as local characteristics of the flow throughout the full LP turbine, in combination with an agile reaction of the search process after dynamically strengthening and/or enforcing new constraints in order to adapt to the review feedback, not only illustrates the feasibility but also the potential of a global design space for the LP module. It is demonstrated that intertwining the capabilities of dynamic SBO and efficient data mining allows to incorporate high-fidelity simulations in design cycle practices of certified engines or novel engine concepts to jointly optimize the multiple stages of the LPT.

The Advanced Heavy Water Reactor (AHWR) is a new power reactor concept being developed at Bhabha Atomic Research Centre, Mumbai. The reactor retains many desirable features of the existing Pressurised Heavy Water Reactor (PHWR), while incorporating new, advanced safety features. The reactor aims to utilise the vast thorium resources available in India. The reactor core will use plutonium as the make-up fuel, while breeding (233)U in situ. On account of this unique combination of fuel materials, the operational characteristics of the fuel as determined by its radioactivity, decay heat and radio-toxicity are being viewed with great interest. Radio-toxicity of the spent fuel is a measure of potential radiological hazard to the members of the public and also important from the ecological point of view. The radio-toxicity of the AHWR fuel is extremely high to start with, being approximately 10(4) times that of the fresh natural U fuel used in a PHWR, and continues to remain relatively high during operation and subsequent cooling. A unique feature of this fuel is the peak observed in its radio-toxicity at approximately 10(5) y of decay cooling. The delayed increase in fuel toxicity has been traced primarily to a build-up of (229)Th, (230)Th and (226)Ra. This phenomenon has been observed earlier for thorium-based fuels and is confirmed for the AHWR fuel. This paper presents radio-toxicity data for AHWR spent fuel up to a period of 10(6) y and the results are compared with the radio-toxicity of PHWR.

Overview of the physics challenges in design of new energy systems