Range Of Pressure Ratios Research Articles

Dynamic characteristics and prediction and control models of subsonic exhaust from a container

This study combines experimental measurements, numerical simulations, and theoretical analysis to investigate the subsonic discharge process in a container under normal temperature and pressure conditions. Experimental data captured the internal pressure dynamics during exhaust at the atmospheric environmental pressure. Numerical simulations using OpenFOAM validated the isothermal exhaust model against the experimental results. Under the assumption of ideal gas and isothermal processes, a nonlinear differential equation was derived to describe the evolution of the container's internal pressure. This equation was simplified for a specific range of pressure ratios, yielding analytical solutions for the internal pressure of the container under both constant and variable external pressures. The effectiveness of the expressions of pressure inside the container was verified by comparing them with experimental and numerical simulation data. We further developed a formula for predicting exhaust mass flow rate, with a prediction error within 9%. An improved formula was subsequently proposed to reduce the error to below 0.4%, enhancing prediction accuracy. For containers with variable external pressure, a method for controlling the exhaust mass flow rate by predicting external pressure changes was proposed, demonstrating its effectiveness in achieving precise control.

Prediction of Leakage Flow Rate and Blow-Down in Brush Seals via 2D CFD Simulation with Porosity Correction

Brush seals are extensively used in rotating equipment, such as gas turbines and compressors, providing effective sealing while accommodating radial, axial, and angular movements between components. In this study, the performance of brush seals with and without clearances was predicted through axisymmetric 2D computational fluid dynamic (CFD) simulations using a porous media model. Because the accurate modeling of a brush seal requires the appropriate porosity to be determined and the flow resistance to be calculated, a porosity correction was performed based on the brush seal’s geometry and pressure ratio. The corrected porosity was then used to calculate the flow resistance and the leakage flow rate was predicted. Based on the results, the corrected porosity significantly improved the accuracy of the previously unreliable leakage flow rate predictions, regardless of the presence of clearances. For cases with a clearance, the blow-down effect was determined through CFD simulations for the given geometry and was compared with experimental data. The leakage flow rate predictions were highly accurate, with a relative error of less than 5% across a pressure ratio range of 1.5–4.

Effect of Ramp Geometry on Single Expansion Ramp Nozzle Performance Characteristics

In high-speed flight regimes, the drag plays a significant role in determining the overall performance of the aerospace vehicle. One proposed solution is to integrate a single expansion ramp nozzle (SERN) at the aft of the vehicle to mitigate the drag effects. This work investigates the effects of nozzle geometry on flow and performance characteristics of SERN with a thrust-optimized parabolic and minimum-length nozzle ramp contours, which have not been explored with regard to these aspects. A computational study is carried out on these two ramp contours using compressible Reynolds Averaged Navier–Stokes equations over a range of nozzle pressure ratio (NPR). In the tested range of NPR, the restricted shock separation is found to be the chief mode of flow separation in SERN, along with the change in the size of recirculation zone and separation bubble. At NPR 3, the thrust-optimized parabolic ramp contour shows an increment of thrust coefficient by 29.2% over the minimum-length nozzle; whereas at NPR 3.5, the minimum-length nozzle demonstrates an increment of thrust coefficient by 56.3% over the thrust-optimized parabolic at 0-deg M cowl angle. Further, in the tested range of NPR, the minimum-length nozzle shows an improved lift coefficient at 5 deg cowl angle.

Performance Analysis of Wave Rotor Combustor Integration into Baseline Engines: A Comparative Study of Pressure-Gain and Work Cycles

This study presents two concepts for integrating a wave rotor combustor (WRC) into a baseline engine: the wave rotor pressure-gain cycle (WRPGC) and the wave rotor work cycle (WRWC). Performance parameters were calculated under different thermodynamic cycles, and a comparative analysis of the thermodynamic cycles was conducted, considering both the ideal- and actual-loss conditions. Furthermore, the impact of the WRC precompression ratio, turbine inlet temperature, and fixed peak cycle temperature on the thermodynamic-cycle performance was investigated. The results indicate that embedding a WRC into a baseline engine with a compressor pressure ratio higher than 24.0 does not lead to an improvement in the thermal efficiency. However, under a baseline engine pressure ratio of 3.6, the actual-loss WRC cycle achieves efficiency improvements of 40.5% and 49.5% in the WRPGC and WRWC, respectively, compared to the baseline engine cycle. Increasing the wave rotor precompression ratio or the turbine inlet temperature ratio results in greater performance improvements for the WRWC compared to the WRPGC. When the peak cycle temperature of the wave rotor is fixed, there exists a narrow pressure ratio range wherein the WRPGC outperforms the WRWC. Therefore, the WRPGC is more suitable for embedment in baseline engines with lower pressure ratios.

A fast uncertainty quantification methodology and sampling technique for joint probability distribution of the Arrhenius rate expression: a case study applied to H2/CO kinetic mechanism

This work proposes a fast, novel, mathematically robust, and elegant unconstrained Method of Uncertainty Quantification (MUQ) for the temperature-dependent Arrhenius rate constant using Cholesky Decomposition (CD) of the covariance matrix of the Arrhenius parameters. The Arrhenius parameters of a reaction are treated as normally distributed correlated random variables. The MUQ method lends itself to an approach for Sampling of Arrhenius Curves (SAC), which automatically ensures that the generated samples are consistent with the distribution of Arrhenius parameters. The Method of Uncertainty Quantification and Sampling of Arrhenius Curves (MUQ-SAC) is used to train a quadratic polynomial response surface (PRS). Three important classes of Arrhenius curves possible within the SAC method are identified. From the total set of targets, a small subset of targets is first used to study the combinations of different classes of Arrhenius curves and their proportions within the design matrix, which is used to train PRS. Based on this understanding, response surfaces are generated for 64 ignition delay targets (Tig), which comprises of a wide range of pressure (P: 1--32.7 atm), temperature (T: 916-DIFadd-2869 K), and equivalence ratio (ϕ: 0.5--6.11), as well as for 74 laminar flame speed targets (Fls), spanning P: 1--25 atm, T: 285--600 K, and ϕ: 0.6--5. The H 2 /CO sub-mechanism of FFCM1.0 is chosen for the case study in which 22 reactions (66 Arrhenius parameters) are considered active parameters. The quality of the generated PRS is measured using the relative Maximum Residual Error (MRE). The quality of PRS is also checked against the search iterations encountered during mechanism optimisation. Accurate PRS could be generated over the search iterations, validating that the SAC method is able to span the entire uncertainty domain while training the PRS. The implementation of the MUQ-SAC method is made available at https://github.com/KrunalPanchal1995/MUQ-SAC.git.

Mind the gap: non-local cascades and preferential heating in high-β Alfvénic turbulence

ABSTRACT Characterizing the thermodynamics of turbulent plasmas is key to decoding observable signatures from astrophysical systems. In magnetohydrodynamic (MHD) turbulence, non-linear interactions between counter-propagating Alfvén waves cascade energy to smaller spatial scales where dissipation heats the protons and electrons. When the thermal pressure far exceeds the magnetic pressure, linear theory predicts a spectral gap at perpendicular scales near the proton gyroradius where Alfvén waves become non-propagating. For simple models of an MHD turbulent cascade that assume only local non-linear interactions, the cascade halts at this gap, preventing energy from reaching smaller scales where electron dissipation dominates, leading to an overestimate of the proton heating rate. In this work, we demonstrate that non-local contributions to the cascade, specifically large-scale shearing and small-scale diffusion, can bridge the non-propagating gap, allowing the cascade to continue to smaller scales. We provide an updated functional form for the proton-to-electron heating ratio accounting for this non-local energy transfer by evaluating a non-local weakened cascade model over a range of temperature and pressure ratios. In plasmas where the thermal pressure dominates the magnetic pressure, we observe that the proton heating is moderated compared to the significant enhancement predicted by local models.

Multi-objective aerodynamic optimization of expansion–deflection nozzle based on B-spline curves

An expansion–deflection nozzle (EDN) is an altitude-compensated nozzle that can accommodate a wide range of nozzle pressure ratio (NPR) variations. An EDN design with good thrust performance under both high- and low-NPR conditions can effectively improve the launch capability of the vehicle. In this study, a multi-objective aerodynamic optimization design is developed considering the performance of the EDN in both open and closed wake modes. The design method of the outer wall and pintle of the EDN is developed using B-spline curves. The design variables are the coordinates of the control points of the curves, and the objective functions are the thrust efficiencies of the EDN at NPRs of 30 and 400. The nozzle thrust is obtained using a Reynolds Averaged Navier–Stokes (RANS) equation solver and validated by experimental results. A radial basis function neural network and a non-dominated sorting genetic algorithm II (NSGA-II) are used to construct the surrogate model and search for the Pareto front, respectively. The relationship between the nozzle contour geometry and the nozzle thrust characteristics of the four optimised individuals on the Pareto front is discussed and analysed. The results demonstrate the effectiveness of the multi-objective optimization design for an EDN. One of the optimized designs improved the thrust efficiency at NPR = 30 by 3.5 % while improving the thrust efficiency at NPR = 400 by 0.6 %. Moreover, to ensure superior performance of the EDN in both operating modes, the nozzle length and pintle ending angle must be designed as a compromise, whereas a larger nozzle exit angle is favoured for both conditions. This study demonstrates the potential of the B-spline method for nozzle optimization design.

Exergetic efficiency and exergy-based ecological function performance optimizations for two irreversible simple Brayton refrigeration cycle models

Air (Brayton) refrigerator has some application potentials nowadays. Based on two irreversible models of constant- and variable-temperature heat reservoir simple Brayton refrigerators established in previous references, this paper further derives exergetic efficiencies and ecological functions, and provide exergy-based comprehensive comparative analyses and optimizations for the two cycle models. Comparative studies among coefficient of performance (COP), cooling load, exergetic efficiency and ecological function characteristics are performed, including general performance analyses for fixed effectivenesses of heat exchangers and performance optimization by optimizing heat conductance distribution and optimizing heat capacity rate marching between heat-reservoir and working substance. For constant-temperature heat reservoir cycle, when select optimal pressure ratio, exergetic efficiency indicator is more reasonable than cooling load and ecological function indicators. When optimizing heat conductance distribution, cooling load indicator is almost the same as exergetic efficiency indictor. For variable-temperature heat reservoir cycle, the reasonable range of pressure ratio is that slightly larger than optimal one at maximum COP. For fixed pressure ratio, the difference between two optimal heat conductance distributions corresponding maximum cooling load and maximum exergetic efficiency is small. Various fixed design parameters have their influence features on the general performances and optimal performances of the cycle models, they should be considered specifically and pointedly. The major difference comparing with classical thermodynamic analysis is the consideration of heat-transfer loss in heat exchangers herein.

Generation of compressed air by overdriven free-displacer thermocompressors – Experimental investigation of a single stage

A thermocompressor cascade of identical stages has been identified as a promising approach to utilize waste heat for the direct generation of compressed air. This contribution presents the first design, realization and experimental investigation of a single-stage prototype featuring a free displacer oscillating in overdriven mode, which has so far only been devised and analyzed theoretically and by simulations. It is self-excited by the p,V-work generated by its rod, which periodically plunges into the cold cylinder volume. In general, the experimental performance confirms the expectations, as a stable, self-controlled operation is possible within a wide range of pressure ratios and inlet pressure levels. However, the theoretical maximum pressure ratio, at which the machine would inevitably stop, is not reached experimentally. Instead, operation continues at a lower pressure ratio, where the net mass flow drops to zero due to leakage effects. This behavior could be confirmed by an enhanced numerical model. In addition, an automatic, self-excited start by decreasing the pressure ratio could be experimentally confirmed. This is a typical industrial operating scenario, when compressed air is fed to a reservoir and consumption increases. These promising findings strongly suggest the realization and testing of a multi-stage cascade as the next step.

Extensive analysis of the applicability range of the linear kinetic approaches in the case of the pressure driven gas mixture flows

The study of gas mixture flows through micro- and macro-channels remains a very attractive area for theorists and experimentalists worldwide, mainly due to their great practical applicability in several aspects of science and industry. The present work includes a comparative study between the linear (McCormack model) and the nonlinear (DSMC method) kinetic theories of binary gas mixture flows through channels over a wide range of the involved parameters. The results show that the McCormack model is a reliable kinetic model for predicting the gas mixture flow behavior. Specific criteria with respect to the applicability range of the linear kinetic theory of short and long capillaries are proposed. The analysis shows that the separation phenomenon remains strong even in the case of small pressure drops. The applicability range of the linear kinetic theory for binary gas mixture flows driven by large pressure drops is obtained to be smaller compared to that of single gases but still wide enough covering a wide range of pressure ratios. Furthermore, the present work shows that the long capillary theory remains a very powerful tool for studying the gas mixture flow behavior under weak and strong nonequilibrium conditions. This work provides a kinetic database of the linear kinetic data (as supplementary material), which until today is still missing from the literature, and as it is shown throughout this work, it can be used far beyond the restrictions defined by the linear kinetic theory.

Characterization of cavitation zone in cavitating venturi flows: Challenges and road ahead

Dynamic features of a cavitating venturi have been a topic of investigation for the past few decades. This review presents state-of-the-art of experimental and numerical studies in cavitating venturi to address the challenges in understanding flow behavior and developing reliable numerical models. Many experimental studies have shown that two strongly coupled mechanisms, namely, Re-entrant Jet and the bubbly shock influence the cavitation zone behavior. We provide pointers from the past and recent studies to the influence of geometry and operating conditions, introducing changes in cavity oscillation. From an operational viewpoint, the modeling studies need to predict four crucial parameters related to its steady and dynamic operation: choked mass flow rate, operating pressure ratio range, cavitation length, and frequency of cavity oscillations. In this paper, we discuss the possible ways to properly configure a one-dimensional (1D) model, which can be a handy tool for extracting the key integral parameters. Realistic predictions require direct numerical simulations, which is not always an economically viable option. Recent three-dimensional (3D) simulations with compressible formulations for flow field and a cavitation model coupled with large eddy simulations to handle turbulence have achieved some success in predictions. Many simplified approaches have been popular. In this paper, we systematically bring out the predictability limits of popularly used mixture models coupled with cavitation and turbulence in more commonly studied two-dimensional (2D) and fewer three-dimensional geometries. Two-fluid models could provide answers, but further studies are required to mitigate the modeling challenges and to enable realistic predictions of the steady and dynamic features of this elegant flow control device for a chosen application.

The influence of cross shear and contact pressure on the wear of UHMWPE-on-PEEK-OPTIMA™ for use in total knee replacement

PEEK-OPTIMA™ polymer is being considered as an alternative material to cobalt chrome in the femoral component of total knee arthroplasty to give a metal-free knee replacement system. Simple geometry pin-on-plate wear simulation can be used to systematically investigate and understand the wear of materials under many different conditions. The aim of this study was to investigate the wear of UHMWPE-on-PEEK-OPTIMA™ under a range of contact pressure (2.1–80 MPa) and cross-shear ratio (0–0.18) conditions.With increasing contact pressure, there was a trend of decreasing UHMWPE wear factor with a significant difference (p<0.001) in the wear factor of UHMWPE under the different contact pressure conditions of interest. Under uniaxial motion (cross-shear ratio = 0), the wear of UHMWPE was low, introducing multi-axial motion increased the wear of the UHMWPE. There was a significant difference (p<0.01) in the wear factor at different cross-shear ratios however, post hoc analysis showed only the study carried out under unidirectional motion to be significantly different from the other conditions.With varying contact pressure and cross-shear ratio, the wear of UHMWPE against PEEK-OPTIMA™ polymer showed similar trends to previous studies of UHMWPE-on-cobalt chrome.

The oscillating Fischer-Tropsch reaction.

The mechanistic steps that underlie the formation of higher hydrocarbons in catalytic carbon monoxide (CO) hydrogenation at atmospheric pressure over cobalt-based catalysts (Fischer-Tropsch synthesis) have remained poorly understood. We reveal nonisothermal rate-and-selectivity oscillations that are self-sustained over extended periods of time (>24 hours) for a cobalt/cerium oxide catalyst with an atomic ratio of cobalt to cerium of 2:1 (Co2Ce1) at 220°C and equal partial pressures of the reactants. A microkinetic mechanism was used to generate rate-and-selectivity oscillations through forced temperature oscillations. Experimental and theoretical oscillations were in good agreement over an extended range of reactant pressure ratios. Additionally, phase portraits for hydrocarbon production were constructed that support the thermokinetic origin of our rate-and-selectivity oscillations.

Evaluation of generalized k-ω turbulence model in strong separated flow estimation of thrust optimized parabolic nozzle

One of the frequently reported defects of RANS-based turbulence models is overestimation of turbulent kinetic energy production in high speed separated flow problems, which causes significant prediction errors. The correct estimation of such flow in thrust optimized parabolic nozzles extremely depends upon the accurate prediction of the onset of flow separation. In this paper, firstly, the significant error of conventional RANS-based turbulence models is shown to predict the onset of flow separation in this type of nozzles. Then, the prediction accuracy is improved through the modification of the essential parameters of the generalized k-ω (GEKO) turbulence model. It was found that modifying the separation and mixing parameters of the GEKO model to realize the turbulent kinetic energy production resulted in the accurate prediction of onset of flow separation at the extensive range of nozzle pressure ratios. Using this modified model with new coefficients reduced the error of about 30% of the k-ω-sst model in estimating the onset of flow separation. Also, the nozzle pressure value at which the transition from free shock separation (FSS) to restricted shock separation (RSS) occurs is well predicted by this approach. After strengthening the turbulence model, the flow physics has been investigated with increasing and decreasing nozzle chamber pressure. The length of the separation shock and reflected shock waves which impose the presence of FSS or RSS patterns and transitional phenomena are discussed. Our new findings show that unlike the transition from FSS to RSS, the inverse transition from RSS to FSS did not depend on the length of the separation and reflective shocks.

Experimental Study on Mechanical Behavior of Gas Transmission Shield Tunnel Segments

To analyze the mechanical behavior of the shield tunnel segment lining of underwater pipelines, based on the prototype segment structure practically applied in a project, a local model test of the combined shield segment considering front and rear ring staggered joints was designed. The internal forces and strains, joint opening and misalignment, and structural deflection change with the axial pressure ratio at different locations of the segment in the range of axial pressure ratio 0.02–0.54 were investigated, and the final failure form of the segment structure was also obtained. The experiment results show that in the assembly segments, the middle segment has the highest stiffness, followed by the side segments. When the segments are damaged, the maximum opening of the longitudinal joint is 1.75 mm. Because the overall damage of the segments is earlier than the joint damage, it is suggested that the development of structural cracks, joint misalignment, and structural deflection be taken as the basis for evaluating the safety of tunnel segments. When the axial compression ratio is loaded above 0.50, top concrete crush damage occurred in the middle segment, while the concrete on both sides happened to incur an oblique 45° shear damage.

Experimental characterization of cavitation zone and cavity oscillation mechanism transitions in planar cavitating venturis

Cavitating venturi is a passive flow rate anchoring device used in varied industrial applications. The dynamics of the cavitation zone can be of interest to ascertain the controlled operation of cavitating venturi under varying pressure ratios. In the current work, we present the results of the complete characterization of three planar cavitating venturis with different divergent angles. Quasi-steady experiments are conducted for a pressure ratio range of 0.39–0.95 and an inlet Reynolds number range of 7.3 × 104–1.28 × 105. Shadowgraphy and high-speed imaging are used to obtain the cavitation zone length and the oscillation frequencies. Spectral proper orthogonal decomposition and discrete Fourier transform are used to assess the dynamics of the cavitation zone. The cavitation zone behavior has been delineated into three specific zones (named R1, R2, and R3 in this work) during the operation when the cavitation is fully contained within the divergent section. Two Strouhal number ranges (based on the inlet dimensions), StD,in≥ 0.1 for large-scale cloud shedding and StD,in≤ 0.05 for small-scale oscillations of the attached cavity, are ascertained as a primary indicator of the dynamic behavior. The current work confirms that the dynamics is governed by re-entrant jet at high cavitation numbers in R1 and the combined action of the re-entrant jet and the bubbly shock wave (collapse-induced) at low cavitation numbers in R3. The transition in the cavitation zone behavior in R2 primarily causes a shift in the sensitivity of the cavitation zone and the dominant frequencies over the operating pressure ratios. In the present work, we show that the span of the transition region (R2) decreases with an increase in the divergent angle.

Effects of High Rotational Speed on Leakage and Windage Heating of Staggered Labyrinth Seals With Smooth and Honeycomb Lands

Abstract Being an important component of aero-engines, the labyrinth seal has always been the focus of research for leakage characteristics. Rotation is usually neglected or taken for minimal effect on seal leakage in previous studies. However, the effect of high rotational speed is inevitable to understand the leakage characteristics of labyrinth seal accurately. Meanwhile, due to high rotational speed, viscous heat is generated massively to result in the rapid temperature rise of leakage flow. Also, the influence of rotational speed on windage heating inside the seal clearance has not been indicated completely. Therefore, the leakage and windage heating of staggered labyrinth seals with smooth and honeycomb lands were experimentally and numerically studied. The large-scale and multifunctional sealing test rig were employed to carry out the experiments with rotational speed 12,000 rpm and pressure ratio range 1.1–2.2. The simulation data obtained by three-dimensional computational fluid dynamics methodology show great agreement with experimental results. Notably, the leakage coefficient is not monotonically decreasing with increased rotational speed, but exists a maximum peak at RPM = 8000. The variation of axial kinetic energy in seal clearance entrances provides a clear explanation of the phenomenon. Rotational speed plays an important role in windage heating, and honeycomb cell size is of secondary importance. Based on simulation data, the calculating formula of windage heating is fitted and shows great performance. This study can provide theory and data support for the follow-up structural optimum design of the labyrinth seal.

Influence of measurement parameters on hydrogen absorption properties of hydrogen storage alloys

ABSTRACT To predict real-time performance of metal hydride-based systems, La0.9Ce0.1Ni5 and LaNi4.7Al0.3 alloys are opted to investigate the influence of operating temperature and supply pressure on absorption kinetics. For the same, the pressure ratio is varied from 1.5 to 4 by keeping the temperature constant. Later, the operating temperature is varied (20–80°C) for the above range of pressure ratio. The study revealed that the absorption kinetics of metal hydrides is substantially influenced by operating temperature and supply pressure. It is observed that with an increase in pressure ratio (1.5, 2, 2.5, 3, and 3.5), the hydrogen supply pressure increases (9.75, 13, 16.25, 19.5, and 22.75), which creates high driving potential consequently results in faster reaction rates. However, increase in operating temperature (20°C and 40°C) at constant supply pressure (25 bar) results in slower reaction rates due to decrease in driving potential because the equilibrium pressure of La0.9Ce0.1Ni5 is higher at high temperature. The similar effect is obtained for LaNi4.7Al0.3. The experimental measurements are carried out using an in-house Sievert’s apparatus and are compared with numerical results obtained through a mathematical model that results in good agreement.

Statistical characteristics of liquid injection by jet pump in the process of hydrocarbon production

Purpose.To determine the effective range of pressure ratios in the working fluid at the inlet to the jet pump and at its outlet and to determine the numerical characteristics of the random variable – the injection coefficient, provided that the normal distribution law is implemented and rational values of the injection coefficient are achieved, with the determination of the probability of its implementation. The methods. The calculation is carried out using the statistical numerical characteristics of the injection coefficient and the justification of the initial conditions regarding the ratio of pressures at the inlet and outlet of the jet pump. Findings. The operating pressure range is set within (60...160) bar, which corresponds to the throttling pressure when the liquid passes through the nozzle of the jet pump within the limits accepted in the oil industry. The effect on the value of the injection coefficient separately of the pressure at the inlet and outlet of the jet pump, as well as the complex effect with the determination of the probable range of pressure at the inlet within 360...460 bar and at the outlet 330...336 bar, while -the injection ratio varies from 0 to a maximum value of 0.96. The range of variation of the injection coefficient within 3 σ with the centering of the random variable and the determination of the mathematical expectation with the value of 0.48 is constructed. The originality. It was found that within half of the mean square deviation, the established value of the probability of realization of the injection coefficient is 0.383. Within the mean square deviation, the established value of the probability of realizing the injection coefficient is 0.683, which confirms the high probability of realizing the injection coefficient with a centering of 0.48 Practical implementation. The obtained results of the calculations make it possible to substantiate the design parameters and energy parameters of the system of supplying the working fluid from the surface during the design of the pump and the development of the technology of its application with the achievement of rational values of the injection coefficient. This will increase the efficiency of the jet pump for cleaning the near-stem area of the oil well and will contribute to the increase of hydrocarbon production.

Comparison of Secondary Flow Characteristics in Mixed-Flow Turbine between Nozzleless and Symmetric Nozzle Vane Angles under Steady-State Flow at Full Admission

In industrial applications, radial or mixed-flow turbines are frequently used in energy recovery systems, small turbines for producing power, and turbochargers. The implementation of radial or mixed-flow turbines helps to maintain high efficiency at a large range of pressure ratios by reducing the overall turbine losses and secondary flow losses. Numerous findings on secondary flow development research adopting double-entry turbines can be obtained in the public domain, except asymmetric volute, which is less well-researched. The focus of the present work is to investigate the evolution of secondary flows and their losses in a mixed-flow turbine used in an asymmetric volute turbine, by employing an experimentally validated three-dimensional computational fluid dynamics (CFD). The flow topology is analyzed to explain the formation and evolution of flow separations at the pressure, suction, and hub surfaces. As the opening angle of the nozzle vane increases, the incidence angle falls into the positive range while the maximum pressure difference between the shroud and hub decreases by about 40%. The results also show that the development of secondary flow accounts for the majority of losses and induced the centrifugal pressure head influence. The presence of symmetric nozzle vanes in both large and small scrolls is also found to have a significant detrimental effect on the turbine efficiency, which is 4% lower than the nozzleless case. Furthermore, significant flow separation is observed in the symmetrical nozzle vane configuration as opposed to that of nozzleless. In addition, the centrifugal pressure head indicated by the maximum pressure difference between the hub and shroud influences the overall turbine efficiency, as the symmetrical nozzle vane arrangement is introduced with two different turbine rotational speeds of 30 K rpm and 48 K rpm.