Radial Inlet Research Articles

Stall Inception Analysis on Axial Compressors With Different Rotor Loading Distributions Under Radial Inlet Distortions

Abstract Stability studies were conducted on a single-stage, low-speed compressor with different rotor loading-distribution designs under a uniform inlet, 10% intensity, and 20% intensity total tip pressure distortion inlet conditions via numerical calculations, theoretical model predictions, and experimental methods. The steady numerical performance was in basic agreement with experimentally measured performance. The theoretical prediction model showed an error within 1.5%, which is less than that of the steady numerical calculation. The total tip pressure distortion reduced flow stability. Conversely, the design of moving the rotor loading axially rearward significantly improved the flow stability. The blade loading analysis showed that the radial distortion caused a radial redistribution of rotor loading. The increase in the rotor-tip loading due to tip distortion was the main reason for the reduced flow stability. In contrast, the design of moving the rotor loading axially rearward reduced the rotor-tip leading-edge loading, enhancing the flow stability. Moreover, an analysis of the unsteady flow validated the findings of the blade loading analyses. It was found that the periodic evolution of the tip leakage vortex (TLV) had an adverse effect on flow stability. In addition, the modified rotors could prevent the tip leakage flow (TLF) from spilling from the leading edge and prevent the interaction of different diffusing regions, decreasing the probability of flow separation.

Effect of radial inlet distortion on aerodynamic stability in a high load axial flow compressor

Radial inlet distortion induced by boundary layer separation can significantly affect the aerodynamic performance of the compressor. The effect of radial inlet distortion on the flow structure is numerically investigated in a high load axial flow compressor. The inlet boundary is determined by the experimental results at the downstream of the distortion generator. The results reveal that tip distortion leads to a reduction in the stall margin, whereas hub distortion extends it. Radial distortion redistributes the main flow toward undistorted region due to the obstructive effect of lattice ring. The deficit in axial velocity with tip radial distortion causes the rotor to operate at a higher incidence angle near the casing, while hub radial distortion alleviates the tip blade loading. The detailed three-dimensional flow field analysis indicates that increased blade loading with tip distortion shifts the trajectories of both primary and secondary tip leakage flow toward the leading edge, thereby expanding the blockage region. Conversely, hub radial distortion unloads the rotor tip region, thereby reducing the blockage region induced by tip leakage flow. Additionally, with hub distortion, the location of separation line on the blade suction surface moves closer to the leading edge, and the flow separation around the trailing edge is intensified.

Flow stability analysis on low-speed compressor with swept rotor blades under radial inlet distortions

Flow stability enhancement for axial flow compressors under radially distorted inlet conditions through rotor sweep design is an important issue for designers. To investigate the couped effect of rotor swept and radial inlet distortion on flow stability, steady numerical simulations, theoretical model predictions, and experimental validations were conducted for a low-speed, single-stage axial compressor (TA36) under various intensities of tip total pressure distorted inlet conditions with different swept rotor configurations. The steady pressure rise significantly decreases as the intensity of the distortion increases, whereas the rotor sweep has little effect on the pressure rise characteristic. The maximum error via model prediction is 1.25 %, while for steady numerical calculation, it is 3.89 %. Higher intensities of distortion lead to worse flow stability. Under radially distorted inlet conditions, forward sweep enhances flow stability whereas backward sweep further worsens it. What's more, quantitative analysis shows that the stability enhancement of forward sweep cannot fully counteract the adverse impact of radial distortion on flow stability. Elevated rotor tip loading was identified as the primary cause of instability under tip total pressure distorted inlet conditions. Forward sweep can slightly reduce this loading, whereas backward sweep has the opposite effect. Furthermore, the impact of rotor sweep on rotor tip loading intensifies with increasing distortion intensity. Unsteady flow field analysis was conducted. Which shows that radial distortion and blade sweep both affect flow stability by altering the intensity of tip leakage flow.

Transient lubrication analysis of journal-thrust coupled bearing considering time-varying loads and thermal-pressure coupled effect

The journal-thrust coupled bearing (abbreviated as JTC bearing) works at the end of the crankshaft in diesel engine, with the function of carrying radial load and prevent axial movement of the crankshaft. The journal part and the thrust part of this special bearing both form the oil film lubrication when subjected to the time-varying loads in axial and radial directions during the working condition. In this work, the JTC bearing in marine diesel engines was analyzed using a transient thermal elastohydrodynamic (TEHD) lubrication model. The thermal and pressure (thermal-pressure) coupled effects were taken into consideration based on the flow, pressure, and thermal continuity conditions between the journal and thrust parts. Moreover, the transient time-varying load was considered in the lubrication analysis to explore the coupled effect under the actual operating conditions. A test rig was built to validate the established transient TEHD lubrication model for the JTC bearing. The thermal-pressure coupled effect between the journal and thrust parts was found to significantly affect the transient lubrication behaviors of the JTC bearing, which cannot be ignored. Also, different boundary conditions were investigated for the influence of the coupled effect on transient lubrication characteristics, including axial clearances, radial clearances, waveforms of radial load, incline angles and inlet oil temperatures. This work could theoretically support the lubrication design of the JTC bearings used in the diesel engine crankshafts.

Numerical study on the effect of radial inlet chamber on the performance of oblique flow compressor

Numerical study on the effect of radial inlet chamber on the performance of oblique flow compressor

INVESTIGATING THE SUITABILITY OF MULTI-SCROLL VOLUTES FOR IMPROVING SPANWISE INCIDENCE OF MIXED FLOW TURBINE ROTORS WITH VARYING BLADE CONE ANGLES IN AUTOMOTIVE TURBOCHARGING APPLICATIONS

Abstract A Mixed Flow Turbine (MFT) is not constrained to a radial inlet blade angle, providing additional design freedom. As the MFT leading edge varies in radius, the spanwise incidence angle varies, leading to additional separation on the blade suction surface (SS) near the hub because of increasingly positive incidence, most noticeable at off-design conditions. A multi-scroll volute was previously paired with a 45° blade cone angle (Λ) MFT which generated non-uniform spanwise flow that improved off-design efficiency at the cost of peak efficiency. The current study identified the range of blade cone angles that benefitted from a multi-scroll volute to reduce incidence at the hub region. A numerical investigation was conducted which determined the influence a multi-scroll volute can have on MFTs with different blade cone angles. When the MFT with large blade cone angle (Λ=60°) was paired with a multi-scroll volute, the efficiency improved by 2.2%pts at design and 0.5%pts at off-design conditions. The incidence improved and mass flow rate increased at the hub region. The MFT with smaller blade cone angle (Λ=30°) had an efficiency loss of 1.3%pts at design and 0.8%pts at off-design conditions when paired with a multi-scroll volute due to increased incidence within the hub region. The multi-scroll volute concept was shown to offer efficiency improvements for MFTs with larger blade cone angles through better management of the non-uniform spanwise velocity distribution at rotor inlet.

Computational Fluid Dynamics Prediction of Rotordynamic Coefficients for Grooved Seals: Model and Numerical Sensitivity

Abstract Computational fluid dynamics (CFD) studies for annular seals continues to gain popularity as a powerful tool for seal rotordynamic analysis, but the wide variety in setup and modeling choices without sufficient justification prevent more widespread use of these methods. This study applies the quasi-steady (QS) method for rotordynamic coefficient prediction to an incompressible grooved seal model in order to rigorously quantify the influence of various prominent modeling choices on prediction results. Variation of the upstream region configuration confirms the dependence of the cross-coupled stiffness on the development of circumferential velocity, which is a strong function of upstream geometry. An axial inlet upstream region is shown to be a sufficient approximation to a radial inlet with axial symmetry, representative of a back-to-back seal configuration. Significant stiffness variation is observed for particular downstream region configurations, though the additional pressure perturbation is mostly confined to the downstream region itself. When no downstream region is included, sensitivity to the amount of pressure profile blending enforced at the seal outlet plane is demonstrated, further underscoring the need for an experimentally accurate downstream geometry. This is the first paper dedicated to a quantitative sensitivity investigation of this nature specific to incompressible grooved seals that examines upstream and downstream region configuration, rotor centrifugal growth effects, and modeling whirl amplitude. Use of these results will foster more accurate application of the QS method for rotordynamic predictions of incompressible grooved seals, ultimately enabling more widespread use of CFD methods for general seals predictions.

Study on the Influence of Radial Inlet Chamber Splitter Blades on the Oblique Flow Compressor Performance

The oblique flow compressor is one of the important components in the compressed air energy storage (CAES) system. The structural shape of the radial inlet chamber (RIC) directly affects the compressor performance, and a reasonable RIC design should achieve the smallest total pressure loss and outlet distortion as much as possible to meet the structural design. To study the influence of splitter blades, 4 RICs equipped with different numbers of splitter blades are designed, and the performance of 4 RICs and the overall performance of the compressor is calculated. The results show that with the increase in the number of splitter blades, the stall margin increases from 6.3% to 13.94%. At the design point, the isentropic efficiency is highest for the RIC with 17 splitter blades, and the pressure ratio is highest for the RIC with 11 splitter blades. Compared with the direct axial intake mode, the uniformity of the relative leakage distribution and the attack angle distribution of the impeller leading edge under 4 radial intake modes are poor. However, with an increase in the number of splitter blades, the uniformity of the relative tip leakage and the attack angle distribution gradually increase. The flow loss of RIC will increase simultaneously, though the uniformity of the outlet aerodynamic parameters distribution improves, and the influence on the downstream component performance gradually weakens. There is an optimal number of splitter blades in RIC, which balances the total pressure loss and distortion coefficient.

Hydrodynamic instability of premixed tubular flame stabilized in stretched rotating flow

The paper analyzes the hydrodynamic instability of a cylindrical flame stabilized in a converging rotating gas flow simulating the flow in a cyclone combustion chamber. The analysis was carried out within the framework of a two-dimensional model describing the gas flow with radial and tangential supply of combustible gas through the walls of a cylindrical chamber. In the stationary case, the gas flow in combustion products and the combustible mixture is described by the solution for a rotating tornado-shaped vortex. The rotation of the gas creates a centrifugal force, which has a stabilizing effect on the flame perturbations. The dependences of the perturbations growth rate on the wave vector of perturbations, the radial and tangential inlet gas velocities, and other parameters of the problem are obtained. The analytical criterion of neutral stability separating regions of stable flame with respect of any perturbations and flame instability in the plane of radial and tangential velocities is obtained. In the absence of rotation and at the large flame radii, the model converts into the Landau- Darrieus model of flame hydrodynamic instability.

Genetic optimization design for aerodynamic structure of oblique flow compressor radial inlet chamber in compressed air energy storage system

AbstractThe compressor plays a significant role in the compressed air energy storage (CAES) system, and its performance directly determines the overall efficiency of the system and the economy of energy storage. Internal flow losses and outlet distortion due to poor design of its radial inlet chamber (RIC) geometry can degrade the performance of downstream components and reduce compressor unit performance. In this article, a multiobjective optimization design is carried out for the RIC of the oblique flow compressor in CAES system, and a parametric optimization design method of the RIC annular convergent channel meridian profile is developed. The optimal Latin hypercube experimental design (opt LHD) method is used to generate the sample library, and the radial basis function neural network (RBFNN) is used to establish the surrogate model of each design parameter and RIC performance. The multiobjective optimization is executed by the second‐generation non‐dominated sorting genetic algorithm (NSGA‐II). After optimization, the area of the annular convergent channel of the RIC is expanded, the transition of the meridian profile is smoother, the distortion coefficient of the RIC is reduced by 0.58%, and the total pressure loss coefficient is reduced by 16.45%. By using the optimized RIC, the performance of oblique flow compressor has been improved. Compared with the original model, the total pressure ratio and isentropic efficiency of the whole machine at the design point have been increased by 0.6% and 0.32%, respectively.

Analysis of Tangential Leakage Flow Characteristics of Oil-Free Scroll Expander for a Micro-Scale Compressed Air Energy Storage System.

Tangential leakage loss is the primary factor that significantly affects the output performance of oil-free scroll expanders. A scroll expander can function under different operating conditions, and the flow of tangential leakage and generation mechanism is different. This study employed computational fluid dynamics to investigate the unsteady flow characteristics of the tangential leakage flow of a scroll expander with air as the working fluid. Consequently, the effects of different radial gap sizes, rotational speeds, inlet pressures, and temperatures on the tangential leakage were discussed. The tangential leakage decreased with increases in the scroll expander rotational speed, inlet pressure, and temperature, and decreased with decrease in radial clearance. With an equal-proportional increase in radial clearance, the flow form of the gas in the first expansion and back-pressure chambers became more complicated; when the radial clearance increased from 0.2 to 0.5 mm, the volumetric efficiency of the scroll expander decreased by approximately 5.0521%. Moreover, because of the large radial clearance, the tangential leakage flow maintained a subsonic flow. Further, the tangential leakage decreased with increase in rotational speed, and when the rotational speed increased from 2000 to 5000 r/min, the volumetric efficiency increased by approximately 8.7565%.

Investigation of the characteristics of an indirect plasma torch

The main task of creating plasma technologies is to improve the operation parameters of its main element - the plasma torch, which is achieved by designing and constructing its main nodes. The paper analyzes the principles of designing a plasma torch and investigates the characteristics of an arc discharge plasma torch. The possibilities of increasing the thermal stability of the anode structure are considered; the speed and trajectory of powder particles are studied; the axial introduction of the powder through the cathode and the thermal stability of the cathode are studied. Using the finite element method, the effect of the anode shape on the service life of the plasma torch is studied by estimating the heat release power under the condition above the melting temperature of copper (anode). The optimal anode geometry for effective cooling of the unit with radial inlet and outlet of the coolant is determined. The influence of the thermal load on the cathode part of the plasma torch is studied, the thermophysical characteristics of the cathode on the operational characteristics of the plasma torch during the thermal load are taken. The dynamics of the particle by axial injection of the powder through the cathode is calculated, and the dynamics of the heating of the powder particle is determined. The output of the carrier gas is stabilized by a swirler and has great dynamics and is located in the high-temperature part of the arc. The trajectory of the movement of a powder particle in the nozzle area is calculated, which corresponds to the average value of the velocity ≈450-500 m/s. It is found that an increase in the cathode diameter from 3 to 5 mm reduces the thermal load by 50%.

Supercritical carbon dioxide in an array of micro impinging jets

Heat transfer of micro multi-jet with supercritical carbon dioxide is experimentally studied. A thermal micro specimen chip constituting of a concentric distribution of three resistance temperature detectors (RTDs) on a serpentine heater, which was mechanically supported by a 500 µm thick fused silica substrate, was microfabricated and used to obtain the heat transfer coefficient under a range of operating conditions. The jets issued from a concentric array of thirteen micro jets with an interject spacing (S/d) of ∼ 1.5, each measuring ∅205 µm, which were perpendicularly positioned over the temperature sensors with a relative standoff, L/d, of 7.3. The effect of radial position, heat flux, mass flux and inlet pressure on the heat transfer were studied at an inlet temperature of 21.7 °C.Results showed a uniform heat transfer coefficient over the heater with optimum values recorded mostly around the pseudocritical condition. In addition, the heat transfer coefficient increased with pressure above the critical condition, which was tied to a corresponding increase in the pseudocritical temperature. Furthermore, the observed heat transfer characteristics of the micro jet impingement cooling using multi-jet were compared to single jet under the same working conditions. This comparison showed that although the multi-jet ensued a more uniform temperature distribution over the heater, the single jet performed better due to an undermined heat transfer process in the multi-jet — a consequence of the jet-to-jet interaction.

Investigation of the Flow Field and Aerodynamic Load on Impellers under Guide Vanes with a Self-Induced Slot in Compressor Radial Inlet

The flow field and the efficiency of the compressor can be improved and increased by the guide vane in the radial inlet chamber. However, the guide vane generates the wake and results in the rotor–stator interaction, which threatens the safety of the impeller. This paper investigated the guide vane with a self-induced slot (SIS) in a radial inlet, and the self-induced slot was a passive flow control method. Through computational fluid dynamics (CFD) simulation, the radial inlet containing unevenly distributed guide vanes (UGVs) in the hydrogen compressor was studied to clarify the flow phenomenon in the radial inlet and the aerodynamic load on the impellers. The simulation results showed that the self-induced slot did not affect the compressor performance but improved the pure wake style to the weak wake near the shroud region. The aerodynamic load on the impeller leading edge was obtained under different radial inlets through unsteady simulation. The dominant frequency and the pulse amplitude of aerodynamic load were obtained by fast Fourier transforms (FFTs). The SIS model had lower amplitude values at the impeller passing frequency, and the reduction in amplitude was about 18% compared to the UGV model near the impeller shroud region.

Analysis of flow distribution uniformity of parallel tube sets with radial inlet

In this paper, the flow distribution uniformity of parallel tubes with radial inlet is studied. Based on the Fluent simulation module in ANSYS WORKBENCH, the numerical simulation of parallel pipe sets is carried out, and the regularity of flow distribution uniformity of parallel pipe sets at radial inlet under different gas flow rates is obtained. In order to make the obtained law more universal, under the condition of constant simulation conditions, change the inlet position and the number of inlet, through a large number of simulation, get the flow distribution uniformity law under different conditions, and found that these laws have similarity.

Aerodynamics of a partial shrouded low-speed axial flow fan

The fan installed in the outdoor unit of air-conditioning (AC) systems is often partially shrouded to increase the inlet area and allow the installation of a larger upstream heat exchanger. However, the effect of radial inflow from the unshrouded part on the aerodynamic performance of the fan is seldom studied. The current paper studies the flow structure in a partially shrouded fan to understand the effects of radial inlet flow on the main flow and the flow in the tip region. The results showed that the flow from the unshrouded region has the same scale as the axial inflow in a partially shrouded fan. The flow field and tip leakage vortex development in the partially shrouded fan are substantially different and the loss corresponding to the TLV is intensified compared to the fully shrouded one. In a partially shrouded fan, the TLV rolls up adjacent to the tip section due to the interaction with radial inflow and follows the tip chord in the unshrouded part. The TLV then moves away from the suction surface in the shrouded part inducing a large blockage and loss at the fan outlet. A vortex street is created outside the fan by the exiting TLV which restricts the main flow from radial expansion and increases the fan backpressure. The reverse flow near the shroud is mainly driven by the TLV and can be controlled by changing the TLV trajectory.

Design and Computational Fluid Dynamics Analysis of a Novel Compact Mixing Chamber in Blast Furnace Ironmaking

Abstract Homogeneous mixing of hot air from the hot blast stove with suitable quantity of cold air in a mixing chamber is very essential to maintain uniform temperature of hot air at all tuyers of a blast furnace. Proper design of the mixing chamber is very important for stable and efficient operation of blast furnace, lower energy consumption, and lower carbon dioxide emission. Comprehensive understanding of the physics of the mixing process is very essential for efficient design of the mixing chamber. In this paper, computational fluid dynamics (CFD) simulations are conducted to analyze the mixing of hot and cold air in a tangential cold gas inlet type and in a radial cold gas inlet type mixing chambers, which are commonly used in the industry. Results show that both types of mixing chamber produce very non-homogeneous mixture of cold and hot air despite having large mixing length in the long hot blast main. Also, design of a novel compact mixing chamber is presented and CFD analysis of this mixing chamber is conducted. The new mixing chamber is found to produce almost homogeneously mixed air stream within a very short length due to very high turbulence of the intensely swirling air flow. Also, the new mixing chamber is found to save large amount of high-quality thermal energy, which is wasted in the other two designs through the wall of the long hot blast main.

Evaluation of the Self-Cooling Performance of a Flux-Switching Permanent Magnet Machine With Airfoil-Shaped Rotor

The objective of this article is to evaluate the self-cooling performance of a novel integrated flux-switching permanent magnet (FSPM) machine with an airfoil-shaped rotor. The rotor of the proposed integrated machine is functioning as both a rotor of the motor as well as an axial fan. It rotates to draw air from the ambient into the rotor and accelerate the flow through the rotor stage. The high-speed flow provides forced convection to the rotor, stator, windings, and magnets. Therefore, self-cooling is achieved. Accounting for manufacturing challenges of the airfoil blades, three-dimensional (3-D) printed blade caps are designed and assembled over the laminated rotor poles for the airfoil-shaped rotor. The electromagnetic performance of the continuous-skewed stator slot is compared with the step-skewed stator slot. Three housing configurations are proposed in terms of housing with radial inlets, housing with axial inlets, and no housing. The electromagnetic performance is verified by 3-D finite element analysis (FEA). The convective heat transfer coefficients of the three housing configurations are calculated by analytical methods and numerical simulations by 3-D computational fluid dynamics. The effect of encapsulations on the windings is also evaluated by FEA. A prototype machine is built and tested. Experimental results of measured temperature distributions on the stator and windings are included to validate the numerical simulation results.

Experimental Validation of the Aerodynamic Performance of an Innovative Counter-Rotating Centrifugal Compressor

Turbomachinery with double counter-rotating impellers offers more degrees of freedom in the choice of design and control parameters compared to conventional machines. For these innovative machines, the literature review shows that more publications concerning axial type turbomachines are available than centrifugal ones. This work deals with a design and experimental performance analysis, applied to two counter-rotating impellers of a centrifugal compressor “CRCC”. CRCC was designed with a specifically developed tool based on mean-line approach coupled with optimization algorithms and a stream-curvature through-flow method to satisfy the design criteria. This paper presents an experimental validation of the CRCC design tool and its performances against the baseline “SR”, composed of one centrifugal impeller and a volute for which experimental data are available. CRCC numeric simulations are also validated by experimental data. For a fair comparison between CRCC and SR, the same volute is used for both configurations. The CRCC studied here includes a first conventional impeller with an axial inlet and a radial outlet, while the second impeller is parametrically designed and can be considered a rotating bladed diffuser with a radial inlet and outlet. The obtained results show that CRCC can deliver a pressure rise increase of two compared to SR, along with an increase of isentropic efficiency and also validate the design method of this novel layout. The experimental results also show that the speed ratio of CRCC has a positive effect on the surge and shock margin.

Flow Control of Radial Inlet Chamber and Downstream Effects on a Centrifugal Compressor Stage

Radial inlet chambers are widely used in various multistage centrifugal compressors, although they induce extra flow loss and inlet distortions. In this paper, the detailed flow characteristics inside the radial inlet chamber of an industrial centrifugal compressor have been numerically investigated for flow control and performance improvement. First, the numerical results are validated against the experimental data, and flow conditions inside the inlet chambers with different structures are compared. They indicate that, in the non-guide vane scheme, sudden expansions, tangential flows and flow separations in the spiral and annular convergent channels are the major causes of flow loss and distortions, while using guide vanes could introduce additional flow impacts, separations and wakes. Based on the flow analysis, structure improvements have been carried out on the radial inlet chamber, and an average increase of 4.97% has been achieved in the inlet chamber efficiencies over different operating conditions. However, the results further reveal that the increases in the performance and overall flow uniformity just in the radial inlet chamber do not necessarily mean a performance improvement in the downstream components, and the distribution of the positive tangential velocity at the impeller inlet might be a more essential factor for the efficiency of the whole compressor.