Inlet Total Temperature Research Articles

Efficient Uncertainty Quantification and Sensitivity Analysis on the Aerothermal Performance of Turbine Blade Squealer Tip

Abstract It is important to accurately estimate the impact of flow and geometric variations for engineering design and manufacture. In this paper, an efficient uncertainty quantification analysis framework based on the combination of Universal Kriging (UK) metamodels and sparse Polynomial Chaos Expansion (PCE) is proposed. A challenging analytical test function and an engineering test are considered to investigate the response performance of the UK-PCE method. Then, this method was applied to the uncertainty quantification on the aerodynamic and heat transfer performance of GE-E3 rotor blade squealer tip. Meanwhile, a global parameter sensitivity analysis using the Sobol Indice method is carried out to identify the key parameters for the aerothermal performance of the squealer tip. Wherein, the inlet total temperature is considered as flow condition uncertainty parameters and tip clearance and cavity depth are considered as geometrical uncertainty parameters. The results show that the UK-PCE method reduces the computational cost by more than 70% in comparison to the typical PCE method. Under the influence of the uncertain geometry and operating conditions, the heat flux of the squealer tip basically conforms to the normal distribution and the statistical mean value of it increased by 5.32% relative to the design value and the probability of it deviating from the design value by 5% is as high as 44.62%. The result of sensitivity analysis reveals that the uncertainty of the aerodynamic characteristics of the squealer tip is almost entirely caused by the tip clearance which accounts for 90.31% and 98.77% of the variance of the leakage flow rate and total pressure loss coefficient. And it is also a key variable for the uncertainty of the heat transfer performance considering that its variance indexes for tip heat flux and blade heat flux are 31.23% and 73.14%, respectively. Finally, the influence mechanisms of the uncertainty parameters on the aerothermal performance of the squealer tip are investigated by detailed flow and thermal field analysis.

Investigations on the aerothermal performance of the turbine blade winglet squealer tip within an uncertainty framework

A improved efficient uncertainty quantification analysis framework is proposed by the combination of sparse Polynomial Chaos Expansion (PCE) and Universal Kriging (UK) metamodel to obtain the surrogate model. Meanwhile a challenging analytical test function and an engineering test are considered to investigate the response performance of UK-PCE method. The results show that the UK-PCE method reduces the computational cost by more than 70% in comparison to the typical PCE method. Then this method was applied to the uncertainty quantification of the effect of the Conventional Squealer Tip (CST) and Winglet Squealer Tip (WST) on the aerodynamic and heat transfer performance of GE-E3 rotor blade tip. Additionally, the Sobol Indice method is carried out as a global parameter sensitivity analysis to identify the key parameters for aerothermal performance of the CST and WST. Wherein, the inlet total pressure, inlet total temperature and inlet flow angle is considered as flow condition uncertainty parameters and tip clearance are considered as geometrical uncertainty parameters. The influence mechanisms of the uncertainty parameters on the aerothermal performance of the CST and WST are investigated by detailed flow and thermal field analysis. According to the results of the uncertainty quantification calculation, the mean values of leakage flow rate of both CST and WST have increased remarkably compared with the design values, and it is worth nothing that the increase of the mean value and the standard deviation of leakage flow rate of WST is much larger than that of CST. Therefore, in actual operation, the ability of WST to control the leakage flow rate will be much lower than expected. Further, the study of heat transfer performance uncertainty quantification shows that the mean value and standard deviation of the heat flux of WST are larger than that of CST, indicating that the use of winglet structure will instead make the heat transfer performance of the blade tip worse in actual operation. The result of sensitivity analysis reveals that the tip clearance is the parameter that contributes most to the uncertainty of the aerothermal performance of CST and WST, so the geometric accuracy of the tip clearance should be strictly ensured in the turbine blade assembly and marching process. What needs to be noted is that the influence of the inlet total temperature on the uncertainty of the heat transfer performance of the CST and WST is also not negligible, hence a satisfactory control system should be designed in the actual operation of gas turbine so the fluctuation of inlet total temperature can be attenuated rapidly.

Effects of the ring clearance on the aerodynamic performance of a CO2 centrifugal compressors annular seal: A numerical study

Computational fluid dynamics simulations are performed on a floating-ring annular seal of a Carbon Dioxide (CO2) centrifugal compressor. The numerical methodology has been validated by comparing the numerical results for the labyrinth function of a stepped-type labyrinth seal with those from experiments. An annular seal of a CO2 compressor is considered and the effects of the rings’ clearances on the seal function are investigated. Results showed that although the leakage rate grows considerably with increasing ring clearance, the leakage function rises marginally with clearance. Furthermore, the leakage function remains almost constant with increasing the inlet total pressure and temperature. Results also showed that the minimum required flow rate of the barrier gas grows substantially with increasing the ring clearance.

Performance characteristics of a divergent vortex tube

In this paper performance characteristics for a Ranque-Hilsch vortex tube are presented. The vortex tube was of divergent design and optimised for both size and performance, to be used to supply cold air to turbomachinery experiments with feed air in the supply pressure range 3.0–7.0 bar, and with overall feed mass flow rates in the range 0.05–0.14 kg/s. Optimum fixed parameters selected from the literature were: the ratio of cold-exit diameter to tube inlet internal diameter (0.50); the ratio of combined inlet-nozzle throat area to the tube inlet internal cross-sectional area (0.22); the vortex tube half-angle (3°); the number of inlet nozzles (6); the half-angle of the hot exhaust conical splitter (45°) and the ratio of tube length to tube inlet internal diameter (20). Free parameters that were investigated were: the overall total-to-static pressure ratio between inlet and cold-exit conditions (3.0, 5.0, and 7.0) and the cold-gas mass fraction (0.0–1.0). Comprehensive experiments were performed to characterise the vortex tube performance in terms of the following parameters: non-dimensional cold and hot-outlet temperatures; non-dimensional cold and hot-gas energy separation; isentropic efficiency referenced to cold-gas expansion; and coefficient of performance (COP). A transient heat flux correction technique was implemented to correct for unsteady heat flux terms from the working gas to the vortex chamber walls. Joule-Thomson effects were accounted for by introducing a corrected inlet total temperature. Cold-exit and hot-exit temperature separations were found to increase with pressure ratio. Non-dimensional cold-exit temperature had a minimum at cold-gas mass fraction of approximately 0.40. Non-dimensional hot-exit temperature increased approximately linearly with cold-gas mass fraction. COP decreased with increasing pressure ratio and had a peak value at cold-gas mass fraction approximately 0.60. Isentropic efficiency was relatively insensitive to pressure ratio and had a peak value at cold-gas mass fraction approximately 0.23. In the range investigated the lowest non-dimensional cold-exit temperature (normalised by inlet temperature) was 0.91, the highest coefficient of performance was 0.097, and the highest isentropic efficiency was 0.23. Full details of the design are given, allowing implementation by other researchers.

Effects of Reversed Shock Waves on Operation Mode in H2/O2 Rotating Detonation Chambers

Operation modes are an important topic in the research of Rotating Detonation Chamber (RDC) as it can affect the stability of RDC. However, they have not been discussed in detail due to the limitation of measurement means in experiments. The aim of this research is to investigate the mechanism of different operation modes by numerical simulation. In this paper, a numerical simulation for RDCs with separate injectors is carried out. Different operation modes and mode switching are analyzed. There is a series of reversed shock waves in the flow field. It was found that they have great effects on operation mode and mode switching in RDCs. A reversed shock wave can transit into a detonation wave after passing through isolated fresh gas region where fresh gas and burnt gas distribute alternatively. This shock-to-detonation transition (SDT) phenomenon will influence the ignition process, contra-rotating waves mode and mode switching in RDCs. SDT makes the number of detonation wave increases, resulting in multi-wave mode with one ignition. Moreover, quenching of detonation waves after collision and SDT after passing through isolated fresh gas region are the mechanism of contra-rotating waves mode in RDCs with separate injectors. In addition, when the inlet total temperature increases, a shock wave is easier to transit into a detonation wave. The distance that a shock wave travels before SDT decreases when temperature increases. This will result in mode switching. Therefore, SDT determines that there is a lower bound of detonation wave number.

A Study on Adapted Similitude Modeling Method of Turboexpander With Different Gas Working Fluids

Abstract The study on similitude modeling method of turboexpander with different working fluids is not only the key technical means and necessary method for the research and development of turboexpander with special working fluids but also an effective way to further expand the application scope of a turboexpander. In this paper, an adapted similitude modeling method (ASMM), which is based on dimensional analysis, actual characteristics of real gas, and seven similitude criteria, is proposed. Based on modeling criterion π4, the new similitude modeling relationship of turboexpander with different gas working fluids is obtained based on rotational speed, inlet total temperature, specific heat ratio, and gas constant. Aiming at the ASMM, the similitude modeling performance of turboexpander with air, methane, CO2, and helium is verified by using the computational fluid dynamics method. The results show that the modeling effects on aerodynamic performance are well predicted in a wide range including the design point (expansion ratio 2.9∼5.0), and the errors of the total-to-total isentropic efficiency, relative equivalent mass flow rate, relative equivalent shaft power are less than 0.74%, 1.94%, and 1.69%, respectively. Methane and CO2 have the best modeling performance, their errors of efficiency, relative equivalent mass flow rate, and relative equivalent shaft power are all less than 0.5%; Furthermore, the ASMM also has pinpoint accuracy with the prediction of the internal flow field, which provides a good idea for further research on special working fluid turboexpander and an approach to expand the application scope of turboexpanders.

A multi-fidelity simulation method research on front variable area bypass injector of an adaptive cycle engine

Front Variable Area Bypass Injector (Front-VABI) is a component of the Adaptive Cycle Engine (ACE) with important variable-cycle features. The performance of Front-VABI has a direct impact on the performance and stability of ACE, but the current ACE performance model uses approximate models for Front-VABI performance calculation. In this work, a multi-fidelity simulation based on a de-coupled method is developed which delivers a more accurate calculation of the Front-VABI performance based on Computational Fluid Dynamics (CFD) simulation. This simulation method proposes a form of Front-VABI characteristic and its matching calculation method between it and the ACE performance model, constructs a coupling method between the (2-D) Front-VABI model and the (0-D) ACE performance model. The result shows, when ACE works in triple bypass mode, the approximate model cannot account for the effect of Front-VABI pressure loss on Core Driven Fan Stage (CDFS) design pressure ratio, and the calculated error of high-pressure turbine inlet total temperature is more than 40 K in mode transition condition (the transition operating condition between triple bypass mode and double bypass mode). In double bypass mode, the approximate model can better simulate the performance of Front-VABI by considering the local loss of area expansion. This method can be applied to the performance-optimized design of Front-VABI and the ACE control law design during mode transition.

Numerical study on unsteady film cooling performance of turbine rotor considering influences of inlet non-uniformities and upstream coolant

High-pressure turbine (HPT) rotor blades work in a harsh environment with high temperature and rotational speed. Affected by blade row interaction and inlet non-uniformities, the rotor flow field behaves with significant unsteady characteristics. In order to study the unsteady film cooling performance of the rotor blade, unsteady numerical simulations were conducted on the film-cooled first stage vane and blade of GE-E3 engine HPT. Time-resolved results of cases with hot streak (HS) and combined HS and swirl were compared to the case with uniform inlet total temperature and velocity to investigate the effect of inlet non-uniformities. A simulation with non-film-cooled stator vane (NFCS) was also studied to reveal the impact of stator film coolant. The results showed that unsteady film cooling effectiveness fluctuations at the leading edge (LE) region are the most significant, with the mean-to-peak fluctuation amplitude reaching over ±100%. LE cooling air unsteady excursion induced by the stagnation line oscillation is the main cause of this behavior. Vane coolant and inlet non-uniformities have shown a distinguished influence on the coolant attachment and migration at LE, thus affecting the film cooling effectiveness. At blade pressure side (PS) and suction side (SS), vane coolant and inlet non-uniformities affect the fluctuation amplitude of film cooling effectiveness by changing the static pressure perturbation behavior. Simultaneously, the existence of HS will decrease the SS time-averaged film effectiveness by a factor of 10%. In comparison, swirl has shown a negative effect on PS film effectiveness by a factor of 6%.

PHANTOM COOLING EFFECTS ON ROTOR BLADE SURFACE HEAT FLUX IN A TRANSONIC FULL SCALE 1+1/2 STAGE ROTATING TURBINE

Abstract An experimental and numerical investigation of phantom cooling effects on cooled and uncooled rotating high pressure turbine blades in a full scale 1+1/2 stage turbine test is carried out. Objectives set to capture, separate, and quantify the effects of upstream vane film-cooling and leakage flows on the downstream rotor blade surface heat flux. Multiple series of tests were carried out in the Air Force Research Laboratory, Turbine Research Facility, at Wright-Patterson Air Force Base, Ohio. A non-proprietary research turbine test article is uniquely instrumented with high frequency double-sided thin film heat flux gauges custom made at AFRL. High bandwidth, time resolved surface heat flux is measured on multiple film-cooled and non-film-cooled HPT rotor blades downstream of both film-cooled and non-film-cooled vane sectors. Upstream wake passing and heat flux is characterized on both rotor pressure and suction side surfaces, along with quantifying rotor phantom cooling effects from non-uniform 1st stage vane film cooling and leakage flows. Fast response heat flux measurements quantify how rotor phantom cooling impacts the blade pressure side greatest; increasing along the pressure side towards the trailing edge. It is discovered upstream vane film-cooling alone can account for 50% of the rotor blade cooling effect, and even outweigh the rotor blade film cooling effect far from the blade showerhead holes. Added unsteady numerical simulation demonstrates how variations in inlet total temperature and incidence angle can also contribute to circumferentially non-uniform rotor heat flux.

Steady active control of noise radiation from highly heated supersonic jets.

The goal of the present investigation is to study the effect of using fluid inserts for noise control at high exhaust temperatures by performing a sequence of large eddy simulations on a typical military-style nozzle, both with and without fluid inserts, at jet inlet total temperature ratios of 2.5, 5, and 7. An exact physics-based splitting of the jet flow-field into its hydrodynamic, acoustic, and thermal components reveals clear evidence of a reduction in the radiation efficiency of Mach waves from the controlled jet. This effect is far more pronounced at afterburner conditions, where the location of the maximum noise reduction is observed to shift upstream with increase in jet temperature, thus matching the maximum location of the jet OASPL directivity. Moreover, the maximum noise reduction achieved at afterburner conditions exceeds that obtained at lower exhaust temperatures. This is encouraging and shows that the effectiveness of the fluid inserts improves with an increase in jet exhaust temperature. Furthermore, by accounting for the effect of bleeding off bypass air for the fluid inserts in the LES simulation, this noise reduction is predicted to be achieved at a conservative thrust loss estimate of under 2% at both laboratory and afterburner operating conditions.

선박폐열회수시스템을 위한 외향반경류형 터빈 기본 설계

Based on the IMO 2020 Regulation and EEDI Phase 3, international demand for eco-friendly ships is growing. The waste heat recovery system on vessels has a potential to reduce CO₂ emissions of 5 to 10% while improving engine efficiency. This study aims to design ORC (Organic Rankine Cycle) and radial outflow turbine for the waste heat recovery system using exhaust gas in vessels. A designed cycle is simple ORC using R245fa as a working fluid. 1D turbine design utilizes Euler`s turbomachinery equation, specific speed, specific diameter and commercial software. Once the initial model of the ROT (Radial Outflow Turbine) was designed, a case study was conducted by different numbers of stage. For a case study, we chose a 5-stage ROT and analyzed its design and off-design performances using rotational speed, inlet total pressure and temperature. The designed 5-stage ROT has the power output of 480.9 kW and total-to-static efficiency of 86.8% at the design point. The off-design performance can be a preliminary guidance to operate an ROT in practice.

Thermodynamic analysis and optimization of organic Rankine cycles based on radial-inflow turbine design

In recent years, high-temperature organic Rankine cycle (ORC) with a heat source temperature over 300 °C has attracted interests, which has wide range of applications from industrial point of view. However, few researchers have focused on the coupled design and optimization of the high-temperature ORC system and radial-inflow turbine (RIT). In this work, a coupled design of the ORC system and RIT with the heat source inlet temperatures of 300, 350 and 400 °C is developed using non-dominated sorting genetic algorithm. The ORC thermal efficiency and turbine performance factor (PF) are introduced as optimization objectives. Two mixtures of siloxanes, seven pure siloxanes and nine pure hydrocarbons are considered as working fluid candidates. In addition, the thermodynamic comparison between mixtures of siloxanes and pure working fluids is presented. Moreover, the influences of the turbine inlet total temperature, total-to-static expansion ratio, and specific speed on the ORC thermal efficiency, turbine performance, and turbine size are investigated. The results show that the turbine power output and cycle thermal efficiency are more sensitive to the expansion ratio while turbine size is more sensitive to the turbine inlet total temperature and specific speed. In addition, PF increases with the rise of the turbine inlet total temperature, expansion ratio and specific speed. Moreover, compared with pure working fluids, mixtures of siloxanes have higher efficiencies, but larger turbine and heat exchanger size. Cyclohexane, toluene, m-xylene and hexane with higher PF and smaller size of turbine and heat exchanger are promising working fluids in applications where the compact turbine and heat exchanger is preferred, such as vehicle waste heat recovery.

Design of a two spool contra-rotating turbine for a turbo-fan engine

Contra-rotating turbines offer enhanced performance over their conventional co-rotating configurations. In addition, vaneless contra-rotating turbine stages offer lesser stage length along with improved performance. Contra-rotating turbines with a vaned LP stages offer a controlled work-split between the stages over a wider range of operating conditions by maintaining inlet swirl to the second rotor. The objective of the present work is to design an equivalent vaned contra-rotating turbine for an existing co-rotating configuration of a two-spool turbo fan engine. The contra-rotating turbine is designed by retaining the existing flow path and HP turbine, and redesigning the LP turbine for fixed radial distributions of inlet total temperature, pressure and swirl. A comparative study between performance of the co-rotating and contra-rotating turbines is carried out for different speeds. Cascade testing of the LP stator and rotor mean sections was carried out to validate the analysis. The LP stage of contra-rotating turbine exhibits a performance improvement by 2% points at design point, as per flow predictions. The reduced flow deflection in stator row is the primary reason for significant reduction in profile and secondary losses in contra-rotating turbine, which contributed to the performance improvement. A significant reduction of 23% in blade weight and 45% in LP stator vane count is obtained.

Analysis of ultra-low uncertainty gas turbine flow capacity measurement techniques

Accurate assessment of nozzle guide vane (NGV) capacity is essential for understanding engine performance data, and to achieve accurate turbine stage matching. In accelerated engine development programmes in particular, accurate and early assessment of NGV capacity is a significant advantage. Whilst the capabilities of computational methods have improved rapidly in recent years, the accuracy of absolute capacity prediction capability is lower than experimental techniques by some margin. Thus, experimental measurement of NGV capacity is still regarded as an essential part of many engine programmes. The semi-transient capacity measurement technique, developed and refined at the University of Oxford over the last 10 years, allows rapid and accurate measurement of engine component (typically fully cooled NGVs) capacity at engine-representative conditions of Mach and Reynolds numbers and coolant-to-mainstream pressure ratio. The technique has been demonstrated to offer considerable advantages over traditional (industrial steady-state) techniques in terms of accuracy, time and operating cost. Since the original facility was constructed, the facility has been modularised to allow for rapid interchange of test vane modules, and the instrumentation has been optimised to drive down the uncertainty in NGV capacity. In this paper, these improvements are described in detail, and a detailed uncertainty analysis is presented of the original facility, the current facility, and a proposed future facility in which the uncertainty of the measurement has been driven down to a practical limit. The bias errors of the three facilities are determined to be ±0.535%, ± 0.495% and ±0.301%, respectively (to 95% confidence). The corresponding precision uncertainties are ±0.028%, ±0.025% and ±0.025%, respectively. The extremely low precision uncertainty in particular allows very small changes in capacity to be resolved. This, combined with rapid interchangeability of test modules, allows studies of the sensitivity of capacity to secondary influences with much greater flexibility than was previously possible. Consideration is also given to the definition of vane capacity in systems with several streams at different conditions of inlet total pressure and temperature. A typical high pressure (HP) NGV has three distinct streams: a mainstream flow; coolant flow ejected from film cooling holes (distributed over the vane surface); and trailing edge coolant ejection. Whilst it is helpful for the coolant mass flow rates and inlet temperatures to be included in the definition, only a relatively small difference arises from the way in which this is achieved. Several definitions appear to share similar usefulness in terms of their robustness to changing inlet conditions of individual streams, but the favoured definition offers the possibility of isolating sensitivities to key effects such as trailing edge coolant ejection. This is achieved by explicitly expressing vane capacity as a function of two controlling pressure ratios. The overall purpose of this paper is to review and analyse in detail the current state-of-the-art in gas turbine flow capacity measurement.

Numerical aero-thermal study of high-pressure turbine nozzle guide vane: Effects of inflow conditions

Accurate predictability of high-pressure turbine nozzle guide vane aero-thermal performance is highly desired in the development campaign due to the exposure of the component to a frequent and high heat load. In this paper, the representative vane profile in modern aero-engines is numerically studied. Aerodynamics and aero-thermal validations of the blade profile have been performed in comparison with the available experimental data. It has been shown that a satisfactory agreement could be achieved with the use of the transitional turbulence model shear stress transport γ–θ due to its superiority in capturing the laminar–turbulent transition. Sensitivity studies on the increase in the inlet turbulence intensity, inlet endwall boundary layer thickness, and inlet total temperature profile have been performed to understand the impact of inflow conditions’ uncertainty on the aero-thermal predictability. Increasing the inlet turbulence intensity increases the pressure surface heat transfer coefficient and induces an earlier transition onset on the suction surface. Due to the rapid decay of turbulence intensity in the numerical model, the use of an artificially high inlet turbulence intensity has been shown to be effective in the prediction improvement. On the other hand, the change in the inlet boundary layer thickness influences the formation and strength of the secondary flow, namely, horseshoe vortex and passage vortex. These secondary flow phenomena affect the local blade surface heat transfer coefficient in the near-endwall region although the most significant rise in heat transfer is found on the endwall. The temperature distortion amplitude of a hot streak and its relative clocking position with the vane significantly affect the heat flux distribution. In contrast, the heat transfer coefficient is less sensitive to the change in hot streak conditions. However, it has been shown that increasing the temperature distortion amplitude could induce a larger difference among different clocking configurations. In addition, decreasing the difference between the fluid and wall temperature would delay the transition onset and stabilize the boundary layer. Further analysis of the unsteady effects has been carried out by comparing the steady and time-averaged flow solutions. It has been observed that the discrepancy between these solutions is attributed to the flow field nonlinearity. Thus, a significant discrepancy can be found in the laminar–turbulent transition as well as in the trailing edge region. However, since the contribution of these regions on the total area-averaged heat transfer is small, their influence on the total vane heat transfer is limited.

Fluid Thermal Effect on Non-contacting Labyrinth Seal of 20 MW Steam Turbine

This paper is divided into two parts; the first describes a CFD analysis of a gland packing labyrinth seals in 20 MW steam turbine in LNG plant using ANSYS CFX code as an isothermal simulation in fluid domain. The results of two turbulence models k-ε and k-ω SST are compared and validated against experimental data. It is shown that the labyrinth seal leakage is proportional to the clearance cube so any variation in clearance can have a significant impact on the steam leakage. This clearance between the shaft and the labyrinth seal vary as a function of operating temperature due to the different rates of thermal expansion of the materials for these two components. Likewise the fluid temperature has a direct effect on fluid dynamic behavior. For that; the second part of the paper investigates the effect of fluid thermal conditions of the labyrinth seal via the heat transfer and Nusselt number variation in the stator and the rotor, for different cases of inlet temperature (400 °C, 200 °C, 100 °C, 50 °C) and pressure ratio (2.5, 4.5, 6.5) for an ideal gas. Also it is important to know the temperature distribution across tooth and cavities of the labyrinth seal, and finally the Influence of Inlet total temperature on fluid pressure drop in the labyrinth seal will be treated for improving and readjusting the steam turbine sealing system.

Fundamental experiments of radio‐frequency preionized inert gas plasma MHD electrical power generation

AbstractA seed‐free radio‐frequency (RF) preionized inert gas plasma MHD electrical power generation has been first demonstrated in fundamental experiments with a shock‐tunnel facility. An enthalpy extraction ratio of 2.6% was successfully obtained even under an inlet total temperature of 2200 K at which the power generation can be operated continuously. Since the RF input power required for the preionization tends to be increased for lower inlet total temperature, the reduction of the RF input power is needed for further improvement in the total performance.

Uncertainty Quantification in high-density fluid radial-inflow turbines for renewable low-grade temperature cycles

The inclusion of uncertainties in the design of turbines for renewable low-grade temperature power cycles is becoming a crucial aspect in the development of robust and reliable power blocks capable of handling a better range of efficiencies over a wider range of operational conditions. Modelling high-density fluids using existing Equations of State adds complexity to improving the system efficiency and little is known on the effect that the uncertainties of Equations of State parameters may have on the turbine efficiency. The purpose of this paper is to quantify the influence of coupled uncertain variables on the total-to-static efficiency of a radial-inflow Organic Rankine Cycle turbine with a high-density fluid R143a in a low-grade temperature renewable power block. To this end, a stochastic solution is obtained by combining a multi-dimensional generalized Polynomial Chaos approach with a full three-dimensional viscous turbulent Computational Fluid Dynamics solver for high-density radial-inflow turbines. Both operational conditions (inlet total temperature, rotational speed and mass flow rate) and Equations of State parameters (critical pressure and critical temperature) are investigated, highlighting their importance for turbine efficiency based on the consideration of three Equations of State, namely, Peng-Robinson, Soave-Redlich-Kwong, and HHEOS. This study, which is performed for both nominal and off-design operational conditions, highlights the inlet temperature as the most influential operational uncertain parameters, while the critical pressure is the most sensitive parameter for the three Equations of State tested. More importantly, it demonstrates a higher level of sensitivity of the SRK Equations of State, in particular at off-design operational conditions. This is a crucial aspect to take into account for the robust designs of Organic Rankine Cycle turbines for low-grade temperature renewable power cycles working at various conditions. It is expected that the proposed stochastic approach may consequently positively support the renewable energy sector to develop more robust and viable systems.

Investigation of the Pressure Gain Characteristics and Cycle Performance in Gas Turbines Based on Interstage Bleeding Rotating Detonation Combustion.

To further improve the cycle performance of gas turbines, a gas turbine cycle model based on interstage bleeding rotating detonation combustion was established using methane as fuel. Combined with a series of two-dimensional numerical simulations of a rotating detonation combustor (RDC) and calculations of cycle parameters, the pressure gain characteristics and cycle performance were investigated at different compressor pressure ratios in the study. The results showed that pressure gain characteristic of interstage bleeding RDC contributed to an obvious performance improvement in the rotating detonation gas turbine cycle compared with the conventional gas turbine cycle. The decrease of compressor pressure ratio had a positive influence on the performance improvement in the rotating detonation gas turbine cycle. With the decrease of compressor pressure ratio, the pressurization ratio of the RDC increased and finally made the power generation and cycle efficiency enhancement rates display uptrends. Under the calculated conditions, the pressurization ratios of RDC were all higher than 1.77, the decreases of turbine inlet total temperature were all more than 19 K, the power generation enhancements were all beyond 400 kW and the cycle efficiency enhancement rates were all greater than 6.72%.

Numerical Investigation of a Steam Nozzle with Focus on Non-Equilibrium Condensation and Unsteady Flow Behavior

Present work analyses the condensation of superheated water vapor in supersonic Barschdorff nozzle. The influence of pneumatic mounts in 3D laval nozzle is analyzed using steady and unsteady two phase non-equilibrium condensation steam flow model in Ansys CFX16. Mesh independency studies in 2D model showed that at a lower inlet total temperature and very fine mesh (e.g. 100.2°C and 77k mesh elements) there is problem with the convergence using steady simulation. This is possibly due to the ability of very fine mesh to capture the small flow unsteadiness. The variation in location of Wilson’s point, Wilson’s pressure and maximum sub-cooling rate at the centerline of the nozzle is below 1.5%. The 2D CFD nucleation rate is 50% stronger and droplet diameter is 18% higher compared to the 3D CFD results. The deviation in nucleation rate and droplet diameter at nozzle outlet is the result of dissipation due to wing structure in the 3D model. Nucleation zone predicted by Ansys CFX16 is far upstream the experimental one. Different correction factors in modified nucleation model were used to fit the computed pressure distribution with the experimental one. The correction factor is dependent on boundary conditions and nozzle profile. It is thus concluded that the significance of such correction factor is not unique.