Suction Side Research Articles

Calibration of strain gauges on a model runner blade combining numerical and experimental data

In this paper, we present the calibration setup, method, and results for a set of strain gauges installed on the trailing edge of the runner blades of a model Francis turbine. The calibration work is done as a step in the HydroFlex project, with the goal of taking experimental data to validate numerical models to better estimate the reduction in lifetime from more flexible operation. Due to the complex geometry of the blade, an analytical solution for the stresses for a given load is not possible to obtain, so calibration is needed. A combination of strain measurement and numerical analysis is used to correlate the response from the strain gauges directly to the strains parallel to the trailing edge. The strain gauges are installed on the suction side of the blades, and close to the hub and shroud, and the calibration is done by applying known weights on the shroud using a tailor made blade fixture. The signal from the sensors is passed through a set of miniature amplifiers that fits in the hub of the model runner. The numerical setup is done in ANSYS Mechanical, and is set up to fully replicate the conditions of the physical setup. The results shows that the method is viable, however there is a challenge with the response, and thus required amplification, due to the stiffness of the runner blade material.

Numerical flow field investigation around guide vane of a high head Francis turbine

Guide vanes are the most eroded component of the Francis turbine, and flow instabilities around guide vanes influence the flow field at the runner inlet. Guide vane cascade can be considered an alternative method to investigate the flow field, which maintains flow similarity with the prototype turbine. The objective of this paper is to numerically analyze the flow field around the guide vane cascade. A single guide vane cascade numerical model is developed to perform the simulation using commercial software ANSYS 2022. Two turbulence models, shear stress transport k-ω and standard k-ε, perform steady-state simulation at the best efficiency point. The pressure and velocity distribution are obtained at mid-span, and around the pressure and suction sides of the guide vane. Numerical simulation on a scaled prototype full turbine has also been performed to measure the Francis turbine’s torque and efficiency. The modified Bhilangana- III guide vane profile is installed in the B-III hydropower plant in India and taken as a reference Francis turbine. The velocity and pressure distributions obtained around guide vanes of the scaled full turbine are compared with the velocity and pressure distributions of the single guide vane cascade. A difference of 7.25 % in maximum velocity and 9.40 % in maximum pressure at the mid-span of the guide vane is found between the guide vane cascade and scaled full turbine at the best efficiency point. The overall efficiency of the scaled turbine is also measured, and a difference of 0.83 % between the numerical result and scaled hill chart at the best efficiency point was found.

Numerical Simulation Study on Flow Characteristics of Multistage Centrifugal Pumps under Different Inlet Gas Void Fractions

The flow characteristics of multistage centrifugal pumps in transporting gas–liquid mixed media are highly complex; particularly, the unstable flow of the passage at high gas contents exacerbates energy losses, leading to a decrease in pump efficiency and stability. The excess energy loss in the pump is not conducive to the concept of sustainable development. In this study, a numerical simulation of multistage centrifugal pumps was conducted based on the Euler–Euler heterogeneous two-fluid model. This research revealed that gas primarily accumulates on the suction side of each impeller stage, and the gas distribution decreases progressively with each stage. As the interstage gas volume fraction (IGVF) increases, the gas accumulation within the pump becomes more pronounced. The gas volume fraction of each component is negatively correlated with the flow rate, and the change is more obvious in the impeller. The turbulent kinetic energy distribution inside the impeller is positively correlated with the gas distribution. There is a large fluctuation at 0.6Q and 0.8Q, and the distribution of the impeller vortex is asymmetric. However, the impeller has a lower turbulent kinetic energy near 1.2Q, which indicates that the emergence of gas in the medium increases the high-efficiency area of the multistage pump to a certain extent. This paper reveals how the gas phase is distributed, how energy is lost in the multistage pump, and the gas–liquid two-phase flow characteristics in the pump, which have certain guiding significance for the design and working-condition adjustments of the gas–liquid mixed pump.

Impact of Swirling Flow on the Overall Cooling Effectiveness and TBCs Insulation Characteristics of Turbine Vane

Modern gas turbines find extensive applications in aero engines, power generation, marine, and various other industries. Most numerical studies concentrate on turbine aero-thermal performance under different external conditions with vane or coupon; there are a few published results on combustor-turbine interactions. This study reveals the cooling performance of the first stage with or without coatings to provide a reference for high-performance combustors and turbine-integrated design. The results of the study show that (1) The velocity and temperature distribution inside the combustion chamber are obviously affected by the swirling flow. A central recirculation zone is formed near the central axis, and two external recirculation zones are formed between the inlet section of the combustion chamber and the fluid reattachment point. (2) Inside the combustion chamber, the flame temperature in the central recirculation zone is relatively high, and the range of the high-temperature zone expands with the increase of axial distance. Increasing the swirl number decreases the peak temperature level in the combustion chamber. (3) Under the influence of swirl number, the greater the swirl number, the greater the cooling effectiveness of most areas on the vane surface. (4) In regions where there is a decrease in local heat flux, positive values are evident. This suggests that the application of a coating in these areas results in a reduction of heat transfer from the vane to the mainstream. (5) When comparing the coated vane to the uncoated vane, the cooling effectiveness across the entire surface is notably enhanced, with a particularly significant improvement observed on the vane’s suction side. With the increase of Cax, the difference in cooling effectiveness increment under different swirl numbers also increases.

RANS Prediction of Losses and Transition Onset in a High-Speed Low-Pressure Turbine Cascade

Current trends in aero-engine design are oriented at designing high-lift low-pressure turbine blades to reduce engine weight and dimensions. Therefore, the validation of numerical methods able to correctly capture the boundary layer transition at cruise conditions with a steady inflow for high-speed blades is of great relevance for turbine designers. The present paper details numerical simulations of a novel open-access high-speed low-pressure turbine test case that are performed using RANS-based transition models. The test case is the SPLEEN C1 cascade, tested in transonic conditions at the von Karman Institute for Fluid Dynamics. Both physics-based and correlation-based transition models are employed to predict blade loading, boundary layer characteristics, and wake development. 2D simulations are run for a wide range of operating conditions ranging from low to high transonic Mach numbers (0.7–0.95) and from low to moderate Reynolds numbers (70,000–120,000). The γ-Re˜θt transition model shows a good performance over the whole range of simulated operating conditions, thus demonstrating a good capability in both reproducing blade loading and average losses, although the wake’s width is underestimated. This leads to an overestimation of the total pressure deficit in the center of the wake which can exceed experimental measurements by more than 50%. On the other hand, the k-ν2-ω model achieves satisfactory results at Ma6,is = 0.95, where the boundary layer state is affected by the presence of a weak shock impinging on the blade suction side which thickens the boundary layer, leading to a predicted shape factor equal to five, downstream of the shock. However, at low and moderate Mach numbers, the k-ν2-ω model predicts long or open separation bubbles contrary to the experimental findings, thus indicating insufficient turbulence production downstream of the boundary layer separation. The slow boundary layer transition in the aft region of the suction side that is exhibited by the k-ν2-ω model also affects the prediction of the outlet flow, featuring large peaks of a total pressure deficit if compared to both the experimental measurements and the γ-Re˜θt predictions. For the k-ν2-ω model, the maximum overestimation of the total pressure deficit is approximately 60%.

Accelerated Degradation Test on Electric Scroll Compressor Using Controlled Continuous Liquid Slugging

Refrigerant-based electric scroll compressors are known for their reliability, efficiency, and quiet operation. They are often used in heat pump systems due to their ability to efficiently handle varying levels of load conditions, both for heating and cooling modes of operation. As electric compressors are considered the heart of the heat pump system, being able to determine degradation of compressors prior to failure is of paramount importance for the health of this system. Typical failures for electric scroll compressors range from electrical faults, refrigerant leaks, to mechanical failures and overheating. Specifically, one of the primary failure modes for an electric scroll compressor is mechanical damage due to the high stress effects of refrigerant liquid slugging. These stresses are due to excessively high internal pressures exhibited on the compressor scrolls, which are generated by compressing liquid refrigerant at the suction side of the compressor. This paper provides a new testing methodology that introduces liquid slugging at various degrees of refrigerant quality to degrade a compressor to near the end of useful life. Furthermore, this test aims to determine specific operating conditions and signals that can indicate early compressor degradation. This fault injection configuration consists of a modified heat pump system with the addition of two low pressure heat exchangers added in parallel (with respective electronically controlled expansion valve for each heat exchanger) used to control the refrigerant quality during compressor operations. For a given refrigerant quality, the heat pump system was operated at a fixed compressor performance conditions to sustain liquid slugging for a fixed duration. Afterwards, refrigerant was controlled to be pure vapor at the compressor suction side and the compressor was controlled at several different performance conditions (i.e., fixed compressor suction superheat temperature and compressor pressure ratios, at various compressor speeds), so as to duplicate conditions known to us from the compressor component data sheet for an ideal electric scroll compressor. Through these tests, the results show that the severity of scroll failures depend heavily on the refrigerant quality and the amount of liquid slugging exposure time. Furthermore, symptoms of compressor degradation are detected using the following signals: i) temperature and pressure at the compressor suction side, ii) temperature and pressure at the compressor discharge side, and iii) electric compressor speed and power consumption. To further aid in determining the compressor degradation ground truth, complete compressor teardown was performed to identify sections within the compressor that exhibited significant amounts of wear as compared to a stock compressor.

A comprehensive deviation analysis of film cooling effectiveness measurements using pressure sensitive paint under various conditions

The application of pressure-sensitive paint (PSP) has been extensively utilized to measure the effectiveness of film cooling. During the experiment, the pressure fields for the air-jet case and the foreign-gas-jet case are usually assumed to be identical. However, when there is a disparity in density between the foreign gas and the air, the difference in pressure distributions cannot be disregarded in high-speed or complex flow conditions. The film cooling effectiveness deviation caused by pressure variation was analyzed by formula derivation. The deviation distribution was obtained through the numerical simulation of the experimental process. The results indicated that the deviation is universal under various conditions. For the film cooling on a flat plate, there is a butterfly-shaped negative deviation region and a narrow symmetrical positive deviation zone. The presence of the compound angle significantly increases the deviation and results in a positive deviation region upstream of the hole. The measurement deviation is widely distributed and exhibits significant magnitudes on the blade tip. The deviation range on the suction side is primarily concentrated near the hole. Specifically, the deviation on the pressure side can be almost neglected. A correction method is proposed, involving the use of an oxygen mixture with the same density as the foreign gas and the same oxygen mole fraction as air. This method proves effective in significantly reducing the deviation in all cases.

The acoustic signature of a rudder in the wake of a propeller: Comparison between infinite and semi-infinite approximations

The acoustic analogy is adopted to reconstruct the sound pressure levels from a propeller–rudder system, using the database of instantaneous realizations of the solution from Large-Eddy Simulations, conducted on a cylindrical grid of 3.8 billion points. Results are compared across incidence angles and rudder geometries, approximated by hydrofoils of infinite and semi-infinite spanwise extents. The latter parameter does not affect significantly the acoustic pressure at no incidence, but its influence grows for increasing angles. Actually, trends are different at inner and outer radii. In the vicinity of the propeller wake, the acoustic signature is dominated by the non-linear sources of sound and is higher when the infinite approximation of the rudder geometry is considered, due to the massive separation affecting the suction side of the hydrofoil. In contrast, moving away along the radial direction the lead goes to the linear sources of sound on the surface of the hydrofoil, which are higher in the case of the semi-infinite approximation of the rudder. Surprisingly, separation phenomena, more significant on the suction side of the infinite hydrofoil, result in a lower loading component of the sound, at least in the range of low frequencies considered in the present study, maybe due to a shift of the acoustic signature of the system towards higher frequencies.

Numerical study of an acoustic field effect on boundary layer transition mechanism

The laminar-to-turbulent transition mechanism is fundamentally important for the concepts aiming at reducing CO2 emissions and noise pollution. This research is focused on understanding the acoustic excitation effect on the transition mechanism with a laminar separation bubble. The transition over the suction side of the NACA 0012 airfoil at an angle of attack of 2 degrees and Reynolds number of 2 × 105 with zero free-stream turbulence intensity is considered. The investigation is performed based on three flow cases obtained for a smooth and wavy surface modified airfoils using the large-eddy simulation method. The acoustic excitation is controlled by keeping or removing a naturally occurring acoustic feedback loop by introducing surface waviness on the airfoil’s pressure side. The flow solution for the standard NACA 0012 airfoil provides the acoustic excitation case, whereas the airfoil with the wavy surface on the pressure side provides the case without acoustic excitation. The results confirm that a shorter separation bubble and earlier laminar-to-turbulent transition can be triggered in response to the acoustic excitation. Furthermore, the coupling of the acoustic field and hydrodynamic instabilities is investigated. Finally, it is shown by referring to experimental data that the Kelvin-Helmholtz instabilities inside the separation bubble are amplified by the acoustic excitation.

Numerical investigation of virtual control surfaces for lift control on NACA0015 airfoil

The plasma actuators as virtual control surfaces are assessed numerically as a means to control the lift of NACA0015 airfoil at the full angle of attack (without stall). The virtual control surface for increasing lift is realized by the pressure side (PS) plasma actuators that induce an upstream jet and the suction side (SS) plasma actuators that induce a downstream jet (SSD plasma actuator), while the one for reducing lift is realized by the SS plasma actuators that induce an upstream jet (SSU plasma actuator). Numerical simulation is achieved by solving the two-dimensional Reynolds averaged Navier–Stokes using the finite volume method. The plasma actuator adopts the empirical model proposed by the author before. The simulation of the air flow was performed for the freestream velocity of 20 m/s (Re=1.03 × 106) and the induced jet momentum coefficient between 0.0846% and 0.9027%. The calculation results show that the optimal number of DBD actuators for increasing the lift is related to the angle of attack. The SS flow separation of the high angle of attack greatly reduces the control effect of the PS actuator, which can be eliminated by arranging the actuators in front of the separation point. Finally, a virtual control surfaces configuration containing three groups of seven plasma actuators is obtained.

Study on full-coverage film cooling characteristics on turbine vanes under the effect of trailing-edge shock wave

In transonic turbines, the oblique shock wave emanating from the stator's trailing edge impinges on the neighboring suction side, which has a complex effect on boundary layer flow. Numerical studies were performed to investigate the influence of oblique shock wave on suction-side film cooling, and the numerical results were validated by model experiments. The sudden increase of static pressure downstream of shock wave is adverse to coolant outflow, and cooling effectiveness shows a notable drop. Furthermore, injecting coolant into boundary layer can increase kinetic energy, and weaken flow separation caused by shock wave. Detailed influences of geometric and thermodynamic parameters on film cooling performance were analyzed. The increase of pressure ratio causes the downward motion of shock wave, which is beneficial to film cooling. The increase of hole size improves cooling effectiveness before shock wave, but reduces cooling effectiveness after shock wave. Cooling effectiveness decreases as hole inclination angle, hole pitch and spacing increases. Adding hole diameter or reducing hole inclination angle, hole pitch and spacing can increase discharge coefficient. Laminated cooling and film cooling were compared. By introducing jet impingement and pin fins, laminated structures can generate higher cooling effectiveness but lower discharge coefficient.

Controlling secondary flow in high-lift low-pressure turbine using boundary-layer slot suction

The design of high-lift Low-Pressure Turbines (LPTs) causes the separation of the boundary layer on the suction side of the blade and leads to a strong secondary flow. This present study aims to minimize secondary losses through endwall slot suction and incoming wakes in a front-loaded high-lift LPT cascade with Zweifel of 1.58 under low Reynolds number of 25000. Two slotted schemes for the boundary layer of the endwall were designed (Plan A and Plan B), and the effects of suction mass flow on secondary flow were studied. The underlying physics of the endwall boundary layer of the suction and secondary flow under unsteady wakes was discussed. The results show that slot suction at the endwall boundary layer can significantly suppress the secondary flow by removing low-momentum fluids. Plans A and B significantly reduced the secondary kinetic energy by 44.2% and 36.9%, respectively, compared with the baseline cascade at the suction mass flow ratios of 1%. With an increase in the mass flow ratio of suction, the secondary flow was gradually reduced in both Plans A and B. It is more beneficial to control the secondary flow to destroy the intersection of the pressure side and suction side of the horseshoe vortex before it develops into a passage vortex. Under unsteady wakes, the combined effects of incoming wakes and endwall boundary layer suction can further suppress the secondary flow at the suction mass flow ratios of 2% for Plan A, because the positive and negative vorticity inside upstream wakes accelerated the mixing of the main flow and secondary flow and thus increased the energy of secondary vortices.

A method proposed to predict particle deposition based on critical viscosity model and roughness height prediction in a turbine cascade

Abstract Particle deposition is a common phenomenon in a turbine cascade. It can change the surface condition, which influences the flow and heat transfer. It is very important to accurately predict the particle deposition and surface condition changes. In this study, a combined particle deposition algorithm is proposed based on the critical viscosity deposition model and roughness height prediction. It couples the influence of surface roughness into the particle deposition. The combined model newly developed is employed for the particle deposition. Its effects in a turbine cascade with the combine model is discussed. The results show the deposition is mainly concentrated on the leading edge of the cascade and the pressure side. Small diameter particles are mainly deposited on the suction side and the large are mainly deposited on the pressure side due to inertial effect. The deposition number increases with the particle diameter. As time goes by, more particles deposit on the wall, which builds roughness height and shows a spreading characteristic. Heat transfer is enhanced by the surface roughness and flow characteristics including separation vortex and leakage vortex, in which flow pattern may dominate the effect. In addition, the separation vortex and leakage vortex have a significant effect on the deposition distribution, especially for smaller diameter particles

Marine propeller optimisation through user interaction and machine learning for advanced blade design scenarios

ABSTRACT The complexity of the marine propeller design process is well recognised and is related to contradicting requirements of the stakeholders, complex physical phenomena, and fast analysis tools, where the latter are preferred due to the strict time limitations under which the entire process is carried out. With all this in mind, an optimisation methodology has been proposed and presented earlier that combines user interactivity with machine learning and proved to be useful for a simple blade design scenario. More specifically, the blade designer manually evaluates the cavitation of the designs during the optimisation and this information is systematically returned into the optimisation algorithm, a process called interactive optimisation. As part of the optimisation, a machine learning pipeline has been implemented in this study, which is used for cavitation evaluation prediction in order to solve the user fatigue problem that is connected to interactive optimisation processes. The proposed methodology is investigated for two case studies of advanced design scenarios, relevant for a real commercial situation, that regard controllable-pitch propellers for ROPAX vessels, and the aim is to obtain a set of optimal, competent blade designs. Both cases represent scenarios with several design variables, objectives and constraints and with conditions that have either suction side or pressure side cavitation. The results show that the proposed methodology can be used as a support tool for the blade designers to, under strict time constraints, find a suitable set of propeller designs, some of which can be considered equal or even superior to the delivered design.

The impact of mainstream ingress on the leakage flow and loss in partial shrouded turbines

The vital source of the leakage loss in shrouded LP turbines is the interaction between the leakage flow and mainstream at the exit cavity and downstream of the rotor tip. This paper numerically investigates the effect of the shroud design on the leakage loss. The results show that the mainstream ingress in the exit cavity is the key flow feature affecting the intensity and the resultant loss of the interaction between the two flows, which is highly intenser in partial shrouded turbines than full shrouded turbines and causes three aspects of impact: Firstly, the abundant amount of ingested mainstream raises the pressure in the exit cavity, reducing the axial leakage flow rate through the sealing structure. However, there is circumferential leakage flow at the rotor trailing edge due to the lack of the blockage of the shroud platform. In addition, the ingested mainstream also develops into backflow and a streamwise vortex in the exit cavity, intensifying the mixing of the leakage flow and mainstream. Thirdly, the pressure raise in the cavity promotes the convergence of the cavity outflow at the suction side of the rotor blade, thus expanding the impact region of the leakage flow and increasing the mixing loss downstream. The above impacts result in an efficiency decrease of up to 0.90% in the partial shrouded turbine compared to the full shrouded turbine. Based on the loss mechanisms of mainstream ingress, this paper presents an optimized shroud design, which can effectively reduce the loss in the rotor tip by suppressing the mainstream ingress phenomenon. In this way, the optimized shroud design has improved considerably the aerodynamic efficiency by about 0.50%.

Feather-inspired flow control device across flight regimes

Bio-inspired flow control strategies can provide a new paradigm of efficiency and adaptability to overcome the operational limitations of traditional flow control. This is particularly useful to small-scale uncrewed aerial vehicles since their mission requirements are rapidly expanding, but they are still limited in terms of agility and adaptability when compared to their biological counterparts, birds. One of the flow control strategies that birds implement is the deployment of covert feathers. In this study, we investigate the performance characteristics and flow physics of torsionally hinged covert-inspired flaps mounted on the suction side of a NACA2414 airfoil across different Reynolds numbers, specifically 200,000 and 1,000. These two Reynolds numbers are representative of different avian flight regimes where covert feathers have been observed to deploy during flight, namely cruising and landing/perching. We performed experiments and simulations where we varied the flap location, the hinge stiffness, and the moment of inertia of the flap to investigate the aerodynamic performance and describe the effects of the structural parameters of the flap on the aerodynamic lift improvements. Results of the study show up to 12% lift improvement post-stall for the flapped cases when compared to the flap-less baseline. The post-stall lift improvement is sensitive to the flap’s structural properties and location. For instance, the hinge stiffness controls the mean deflection angle of the flap, which governs the resulting time-averaged lift improvements. The flap moment of inertia, on the other hand, controls the flap dynamics, which in turn controls the flap’s lift-enhancing mechanism and how the flap affects the instantaneous lift. By examining the time-averaged and instantaneous lift measurement, we uncover the mechanisms by which the covert-inspired flap improves lift and highlights similarities and differences across Reynolds numbers. This article highlights the feasibility of using covert-inspired flaps as flow control across different flight missions and speeds.

Turbine Blade Endwall Heat Transfer and Film Cooling Performance With Multigap Jets and Film Holes

Abstract Due to manufacturing, assembly, and operational conditions, gaps are commonly presented in the turbine components, such as platform blade-to-blade gap (slashface gap) and rim cavity platform gap (slot gap). The coolant ejected through these gaps not only limits hot mainstream gas ingestion into the disk cavity but also has the potential to provide endwall film cooling coverage. Nevertheless, the interaction of these gap flows, predesigned film hole jets, and endwall secondary flows, significantly impacts endwall heat transfer and film cooling performance and leads to a more complicated flow field near endwall. To further understand the endwall flow physics behavior in this complicated flow field, the combined effects of film hole jets and multigap leakages (slashface jet and slot jet) were experimentally studied in a transient wind tunnel with a six-blade linear cascade (nonrotating). The endwall heat transfer was measured and recorded by the IR technique at inlet average turbulence intensity (Tu) of 7.5% and an exit Mach number (Maex) of 0.4. In addition, detailed numerical predictions were also performed to discuss the flow physics near endwall and the multigap leakages behavior. Results indicated that the slashface jet is an essential contributor to endwall film cooling performance in this endwall configuration. The slashface jet delays the development of the film hole jets, leading to an enhancement of film cooling performance downstream of the film holes. Increasing the mass flow ratio of the slashface jet (MFRslashface) can prevent the high-temperature mainstream ingestion, reduce the thermal failure risks, and increase the peak of film cooling effectiveness downstream of the endwall (167% at MFRslashface = 0.5%). Due to the limitation and hindrance impacts of the disk vortex (DV), the cavity vortex (CV), and the suction side leg of the horse-shoe vortex (HV,s), the slot flow is confined to a small region downstream of the slot gap.

Compressibility effects in turbulent channel with weak spanwise rotation using direct numerical simulations

Direct numerical simulations of temporally evolving turbulent channel flows with a weak spanwise rotation are conducted at a rotation number of 0.05 and Mach numbers of 0.3, 1.5, and 3.0 to investigate the influence of compressibility effects on turbulent statistics and large-scale structures. The corresponding Reynolds numbers are 2820, 3000, and 4880. Investigation shows that many asymmetric characteristics for incompressible flow also hold for compressible flow. The mean and fluctuating turbulent statistics distributions are similar to those for incompressible flows and shift from the suction side toward the pressure side. Weak spanwise rotation alters the mean the Mach number. The recovery enthalpy collapses between the pressure and suction sides and is independent of the Mach number. The Reynolds shear stress distributions are similar for compressible flows but with larger slopes than incompressible flows. When introducing semi-local scaling, the turbulent kinetic energy budget at pressure side is insensitive to compressibility effects. The average spanwise spacing of near-wall streaks increases as with the Mach number. The number of Taylor–Görtler vortex pairs is determined primarily by the aspect ratio of the computational domain, and is independent of the compressibility effects.

Effect of Blade Twist on The Flow Characteristics of Gas-Liquid Two-Phase Flow in a Spiral Axial Flow Pump

The mixing of oil and gas forms the foundation of deep-sea oil and gas extraction and transportation. However, traditional conveying equipment has low efficiency and high failure rates. In this study, a spiral axial flow gas and liquid multiphase pump was used as the base model. The Eulerian multiphase flow model and RNG turbulence model were used for numerical simulations to analyze the internal flow field of the multiphase pump. A modification scheme was proposed to twist the airfoil shape and create a twisted vane. The twisted blade with the center of the hub-side flange chord length as the twisting center was twisted in the counterclockwise direction to help reduce the relative volume of gas in the flow channel. When the twisted vane with the hub-side airfoil type trailing edge point as the twisting center was twisted in the suction side direction, it helped to accelerate the movement of the gas-liquid mixture at the trailing edge of the back of the vane and further reduced the low velocity zone at the back of the vane. When the twist center is located at the hub side wing type trailing edge point of the twist vane, the twist degree is 0.214. This results in the maximum head and efficiency of the pump, improves gas phase aggregation phenomenon, and enhances the performance of the multiphase pump.

Effects of the misalignment and axial gap on performance of a cover-plate pre-swirl system with impellers for gas turbine cooling

Impellers are designed and used in the cover-plate cavity of the pre-swirl system of modern gas turbines to keep the circumferential velocity of the airflow consistent with the local velocity of the rotor. This reduces the aerodynamic loss of the pre-swirl air delivery system for turbine cooling and further improves pre-swirl system performance. However, in practical applications, the cover-plate disk with impellers is usually installed and fixed to the turbine disk by buckles, which leads to the possibility of the circumferential position of impellers deviating from the design intention during installation and a certain axial gap between impellers and the turbine disk, resulting in deviations in cooling performance. In this work, low-radius cover-plate pre-swirl systems with and without impellers are compared through numerical simulations, and the effects of the impeller circumferential displacement angle (θ) in the range of −0.5° to 0.5° and the axial gap (Δ) in the range of 0%–25% of the cover-plate cavity width are investigated on the flow characteristics and system cooling performance. Results indicate that the impellers are sensitive to the manufacturing and installation deviations. The non-designed circumferential displacement of the impeller will misalign it with the rotating receiver holes and supply holes, hindering the airflow movement in the radial direction and increasing the back pressure of the impeller. Consequently, the severe vortices on the suction side downstream of the impeller leading edge can occur and the entropy production can increase. Numerical results show that when the impeller is displaced by 0.5° circumferentially, the temperature drop effectiveness decreases significantly, and is about 21% lower than that at the designed condition. Moreover, while the axial gap is small, the overall flow pattern and system temperature drop are only slightly affected. As the axial gap increases, there are more cooling airs flowing through the axial gap and not subject to the work of the impeller. Therefore, the temperature drop starts to fall and the swirl ratio declines. For the system studied, the temperature drop effectiveness decreases by around 7.8% when the axial gap reaches 25% of the cover-plate cavity width.