Relative Circumferential Positions Research Articles

Investigating the mechanism of flow of transonic compact crossover tandem diffuser

Dealing with high transonic airflow at the outlet of a mixed-flow impeller is a challenging issue in research on the design of efficient and compact diffusers. A low aspect ratio and an adverse pressure gradient in the passage of the diffuser can lead to flow separation on the hub side of the bend and the suction side of the aft blade. Tandem blading can be used to attain flow control through an appropriate relative circumferential tandem position (λ). However, a comprehensive understanding of flow in a compact crossover tandem diffuser (CTD) requires further investigation. This study provides a detailed analysis of the mechanism of flow in a compact crossover baseline tandem diffuser (CBTD) as well as the influence of different values of λ on the structure of flow of the CTD. The findings show that the CBTD can suppress secondary flow separation on the hub side of the bend by reasonably distributing the radial load. We also found that a value of λ of 75% can delay the point of separation on the suction side of the aft blade over a wide range of spans, where this inhibits the corner separation vortex and improves the structure of flow and performance of the diffuser. We also preliminarily explore the impacts of excitation of full-span jet intensities with different values of λ on the corner separation vortex on the suction side of the aft blade and offer guidance for the design of a compact and efficient CTD.

Excitation force on a pump-jet propeller: The clocking effect of pre-swirl stator

The impact of the clocking effect of the pre-swirl stator on the excitation force of a pump-jet propeller is investigated in this paper. The clocking effect, a common concept in fluid machinery, is applied and extended to the relative circumferential position between the pre-swirl stator and the submarine hull in this paper. The research is conducted using computational fluid dynamics (CFD) and water tunnel experiments. The CFD results demonstrate that the clocking effect exerts a negligible influence on the steady performance of the pump-jet. However, the excitation force of the rotor is greatly influenced by it. This is due to the fact that the stator, when positioned at various clocking positions, generates different wakes that change the amplitude and phase distribution of the rotor strips’ excitation force. Furthermore, the experimental results demonstrate that the influence of the clocking effect on the duct vibration and the noise radiated by the pump-jet should not be ignored, the trend of which is consistent with that of the excitation force obtained by CFD, thereby establishing a clear correlation between the excitation force and the vibration and noise level. This paper is of guiding significance for the low-noise design of submarine pump-jets.

Influence of Position of Intake Struts on Unsteady Load and Vibration of First-Stage Rotor

To investigate the influence law and mechanism of the relative circumferential position of intake struts on the unsteady load and vibration of the first stage rotor, the first 1.5-stage of a heavy-duty gas turbine compressor with intake struts was numerically simulated. The analysis of the flow field and vibration of the rotor blade reveals that the circumferential position of intake struts has little effect on aerodynamic performance but obviously changes the unsteady load and vibration level of the rotor blade. When strut and inlet guide vane wakes coincide, they are strengthened, resulting in the overall enhancement of the unsteady load and vibration on the rotor blade. The circumferential position of struts changes the combined effect of strut wakes and the first stage stator potential flow on the rotor blade, which has an obvious influence on the unsteady load and vibration in the middle chord length but has little influence on the unsteady load near the leading and trailing edges. Research results provide reference and guidance for the installation of struts.

Optimization of the centrifugal slurry pump through the splitter blades position

Optimal transfer of two-phase solid-liquid flow (slurry flow) has long been a major industrial challenge. Slurry pumps are among the most common types of centrifugal pumps used to deal with this transfer issue. The approach of improving slurry pumps and consequently increasing the efficiency of a flow transmission system requires overcoming the effects of slurry flow such as the reduction in head, efficiency, and wear. This study attempts to investigate the changes in the pump head by modifying the slip factor distribution in the impeller channel. For this purpose, the effect of splitter blades on slip factor distribution to improve the pump head was investigated using numerical simulation tools and validated based on experimental test data. Next, an optimization process was used to determine the characteristics of the splitter (i.e., length, number, and environmental position of the splitter) based on a combination of experimental design methods, surface response, and genetic algorithm. The optimization results indicate that the splitters were in a relative circumferential position of 67.2% to the suction surface of the main blade. Also, the optimal number and length of splitter blades were 6 and 62.8% of the length of the main blades, respectively. Because of adding splitter blades and the reduction in the flow passage, the best efficiency point (BEP) of the slurry pump moved toward lower flow rates. The result of splitter optimization was the increase in pump head from 29.7 m to 31.7 m and the upkeep of efficiency in the initial values.

Statistical analysis of the reproducibility of residual stress measurements in cold extruded parts

Cold extruded components are characterized by residual stresses, which originate from the experienced manufacturing process. For industrial applications, reproducibility and homogeneity of the final components are key aspects for an optimized quality control. Although striving to obtain identical deformation and surface conditions, fluctuation in the manufacturing parameters and contact shear conditions during the forming process may lead to variations of the spatial residual stress distribution in the final product. This could lead to a dependency of the residual stress measurement results on the relative axial and circumferential position on the sample. An attempt to examine this problem is made by the employment of design of experiments (DoE) methods. A statistical analysis of the residual stress results generated through X-Ray diffraction is performed. Additionally, the ability of cold extrusion processes to generate uniform stress states is analyzed on specimens of austenitic stainless steel 1.4404 and possible correlations with the pre-deformed condition are statistically examined. Moreover, the influence of the coating, consisting of oxalate and a MoS2 based lubricant, on the X-Ray diffraction measurements of the surface is investigated.

Numerical simulation and performance optimization of the centrifugal fan in a vacuum cleaner

This paper focuses on the efficiency improvement of a centrifugal fan used in a vacuum cleaner. In order to check the performance of the centrifugal fan system, computational fluid dynamics (CFD) analysis is used. The numerical simulation with CFD tool is carried out with RNG [Formula: see text] two-equation turbulence model based on Reynolds-averaged Navier–Stokes equations. To perform the coupling between rotating impeller and stationary area, the multiple reference frame (MRF) model is used. The numerical results of the fan are validated against with experimental results and are found to be highly reliable. The design and optimization of diffuser and impeller of a centrifugal fan are realized by using numerical investigations. For reducing the kinetic energy loss inside the fan, a guide baffle is added to optimize diffuser. The optimization results show that overall efficiency of the fan is improved by 5.27% and considering the lower efficiency of impeller caused by blockage at the blade inlet, etc., the design of impeller with long-short blades is proposed. Several cases of affecting factors under different operating conditions are simulated. Relative length (denoted as [Formula: see text]) and circumferential position of short blades are chosen as design variables. It is found that the efficiency of a fan with a relative length of 0.7 can be increased by 9.34%, and the best circumferential position of short blades is between two adjacent long blades.

A Comprehensive Investigation of Blade Row Interaction Effects on Stator Loss Utilizing Vane Clocking

Blade row interactions drive the unsteady performance of high-pressure compressors. Vane clocking is the relative circumferential positioning of consecutive stationary vane rows with the same vane count. By altering the upstream vane wake's path with respect to the downstream vane, vane clocking changes the blade row interactions and results in a change in steady total pressure loss on the downstream vane. The open literature lacks a conclusive discussion of the flow physics governing these interactions in compressors. This paper presents the details of a comprehensive vane clocking study on the embedded stage of the Purdue three-stage axial compressor. The steady loss results, including radial total pressure profiles and surface flow visualization, suggest a shift in the stator 2 corner separations occurs between clocking configurations associated with the maximum and minimum total pressure loss. To better understand the flow mechanisms driving the vane clocking effects on the steady stator 2 performance, time-resolved interrogations of the stator 2 inlet flow field, surface pressure unsteadiness, and boundary layer response were conducted. The stator 2 surface flows, both pressure unsteadiness and boundary layer transition, are influenced by vane clocking and interactions between rotor 1 and rotor 2, but neither of these results indicate a cause for the change in steady total pressure loss. Moreover, they are a result of upstream changes in the flow field: the interaction between the stator 1 wake and rotor 2 results in a circumferentially varying pattern which alters the inlet flow field for the downstream row, including the unsteadiness and frequency content in the tip and hub regions. Therefore, under different clocking configurations, stator 2 experiences significantly different inlet blockage and unsteadiness from the rotor 2 tip leakage flow and hub corner separation, which, in turn, shifts the radial blade loading distribution and subsequent loss development of stator 2.

The Interactions of Turbine Hot Streak and Leakage Flow from the Inter-Platform Gap

ABSTRACTThe paper presents the effects of the leakage flow from the inter-platform gap on the migration of hot streak in a first stage turbine by three-dimensional unsteady Reynolds-Averaged Navier-Stokes simulations. Five circumferential positions of the hot streak are considered. The comparisons between the results with/without slot leakage show significant differences. The leakage changes the hot streak in the vane passage significantly and it protects the vane suction surface trailing from the hot gas. The leakage also changes the secondary flow and results in forming a new couple of vortices in the vane passage. In general, rotor passage, the hot gas usually gathers in the rotor hub and the pressure surface. In the present study, the leakage coolant from upstream slot is entrained to the unsteady rotor secondary flows and transported toward the rotor hub and pressure surface effectively. The cooling effect is related to the relative circumferential positions between the hot streaks and slot. When the hot streak is positioned at the slot suction side, the time-averaged temperature reduction on the blade leading edge can be more than twice of that for the hot streak at the slot pressure side.

Simulation of Indexing and Clocking with Harmonic Balance

The aim of this paper is to demonstrate how the harmonic balance method can be used to predict rotor–rotor and stator–stator interactions in turbomachinery. These interactions occur in the form of clocking and indexing. Whereas clocking refers to the dependency of the performance on the relative circumferential positioning of the rotors or stators, the term indexing is used when different blade (or vane) counts lead to an aperiodic time-averaged flow. The approach developed here is closely related to the one presented by He, Chen, Wells, Li, and Ning, who generalised the Nonlinear Harmonic method to zero-frequency disturbances. In particular, configurations with only one passage per blade row are used for the simulations. We validate the methods by means of the simulation of a fan stage configuration with rotationally asymmetric inlet conditions. It is demonstrated that the harmonic balance solver is able to accurately predict the inhomogeneity of the time-averaged flow field in the stator row. Moreover, the results show that the approach offers a considerable gain in computational efficiency.

Impact of inlet distortion on turbocharger compressor stage performance

In a turbocharger system, curved pipes are usually used to connect compressors with other parts due to limited packaging space. It is well known that an elbow can generate flow distortion to and interact with the compressor inducer and therefore deteriorate compressor stage performance. The compressor efficiency change may vary with relative positions of inlet elbow and volute. The compressor’s stable flow range is also possible to vary due to the shift of surge and/or chock points. In this paper, eight relative circumferential positions between the inlet elbow and the volute were studied by 3D numerical simulations with experimental validations. The numerical results confirm that adjusting the inlet bend from one circumferential orientation to others does cause an obvious deviation in the compressor aerodynamic efficiency. The result also indicates that the total pressure deficit and the vortices at the compressor inlet are the main contributors to the compressor operating range. With the numerical findings in this paper which was validated by experimental measurements, it is suggested that unfavorable orientations of an elbow relative to volute should be avoided in an intake system.

Influence of the Distribution of Dual Cascades on Double Vanes Based on the Solid-Liquid Two-Phase Flow

The relative positional relationship between the stay vanes and guide vanes is researched to analyze the impact on the hydraulic performance of the Turbine based on N-S equations and RNG k-ε turbulence model under the conditions of sandy water with the numerical simulation method. There are main five kinds of the relative positional relationship between the dual cascades is used to analyse the trends of the distribution about the pressure and velocity. The relative circumferential positions between the dual cascades have obviously effect on the flow verified. And the velocity vector and the pressure distribution on the surface of the guide vanes are studied further. The results show that energy performance is best if little circumferential position differences between the dual cascades in two typical conditions. However, the distribution about the pressure and velocity is uneven on the active surface of guide vanes, exacerbating the local abrasion of the vanes.

Influence of the Distribution of Dual Cascades on Double Vanes Based on the Solid-Liquid Two-Phase Flow

The relative positional relationship between the stay vanes and guide vanes is researched to analyze the impact on the hydraulic performance of the Turbine based on N-S equations and RNG k-ε turbulence model under the conditions of sandy water with the numerical simulation method.There are main five kinds of the relative positional relationship between the dual cascades is used to analyse the trends of the distribution about the pressure and velocity. The relative circumferential positions between the dual cascades have obviously effect on the flow verified.And the velocity vector and the pressure distribution on the surface of the guide vanes are studied further.The results show that energy performance is best if little circumferential position differences between the dual cascades in two typical conditions.However, thedistribution about the pressure and velocity is uneven on the active surface of guide vanes, exacerbating the local abrasion of the vanes.

Investigation on Influence of Design Parameters for Tandem Cascades Diffuser Using DOE Method

The tandem cascade can be used as an efficient way to improve the compressor load. As for the interaction parameters between two rows of the tandem diffuser, it is known that the relative circumferential position, radial gap between two rows, ratio of chord length of two rows, difference of the stagger angle between the front row and rear row blades have significant impact on the performance of the tandem cascade diffuser. In the literature, there is a lack of references for evaluating quantitatively the influence of important tandem design parameters on the tandem diffuser, and thus the adjustment ranges of the tandem parameters cannot be determined accurately. In order to investigate the influences of the tandem design parameters on the compressor performance, in an economically affordable manner, the influences of the design parameters for the tandem cascades diffuser were investigated by Design of Experiments (DOE) method. The orthogonal experimental designs are performed for the radial gap R between the front row and rear row, inlet stagger angle θ of the rear row and relative circumferential position L between the front row and rear row of the tandem diffuser. The DOE analysis results demonstrate that the inlet stagger angle θ of the rear row has significant influence on the response value of total pressure ratio and isentropic efficiency. The relationship between the design parameters of the tandem diffuser and the compressor performance is obtained from the DOE method. The design parameters are adjusted and determined according to the DOE analysis, and then the validation calculations are carried out. The parameter selection capacity of DOE method has been validated by the results. The design parameters determined from DOE analysis can be effectively used in the design process of the tandem diffuser, with notably reduced amount of simulation of each parameter.

Experimental Investigation of a Truncated Pipe Diffuser With a Tandem Deswirler in a Centrifugal Compressor Stage

The subject of this paper is the experimental investigation of three different geometric configurations of the diffusing system in a high pressure centrifugal compressor stage for a jet engine application. The objective of this study is twofold. On the one hand, it seeks to explain the impact of truncating a diffuser and a redesigned tandem deswirler on the global stage performance; on the other hand, it aims to correlate the performance differences with local flow phenomena. For this purpose, a state-of-the-art centrifugal compressor test rig was used. Particle image velocimetry measurements visualize the separation behavior in the pipe diffuser passage. Thereby it is shown that the truncation of the diffuser changed the boundary conditions for the downstream deswirler including a high incidence. Thus, a new tandem deswirler design was implemented and measured. Moreover, the relative position of the two tandem rows is investigated. An optimal relative circumferential position for the stage efficiency and static pressure rise was found. This paper gives fundamental insight into the physical mechanisms of the influence of three geometric configurations in a centrifugal compressor stage, especially in the pipe diffuser and the deswirler. Hence, this study contributes in furthering knowledge of the fundamental principles of flow phenomena in the diffusing system of a centrifugal compressor.

Numerical Investigation of Low Solidity Vaned Diffuser Performance in a High-Pressure Centrifugal Compressor—Part III: Tandem Vanes

As Part III, following the authors’ previous studies, the aerodynamic performance of two different tandem LSDs (low solidity diffusers), Tandem (A) and (B), in a high-pressure centrifugal compressor was numerically investigated over flow rates from impeller choke to minimal flows available in computation. Tandem (A) was of conventional design where the first row came directly from the authors’ previous studies (Part I Oh and Agrawal, 2007, “Numerical Investigation of Low Solidity Vaned Diffuser Performance in a High-Pressure Centrifugal Compressor - Part I : Influence of Vane Solidity,” ASME Paper No. GT2007-27260, and Part II: Oh et al., 2008, “Numerical Investigation of Low Solidity Vaned Diffuser Performance in a High-Pressure Centrifugal Compressor - Part II : Influence of Vane Stagger,” ASME Paper No. GT2008-50178) selected as the highest efficiency vane at design flow, and the second row was designed to be added considering flow conditions at the exit of the first row vane. Tandem (B) followed a creative patent-pending concept where the number of the first row vanes was doubled with much smaller vane chord keeping a low solidity. A position parameter of RCP (relative circumferential position) was introduced to see the effect of the relative location of the second row vane. Using an in-house Navier-Stokes solver with finite volume time marching methods, overall performance was predicted to be compared with each other. Detailed investigation on the behavior of the static pressure recovery and the total pressure loss coefficient in both diffuser designs helps determine why Tandem (A) design is better and the case of RCP = 0.3 gives the best performance.

A hot-streak (combustor) simulator suited to aerodynamic performance measurements

A new hot-streak (combustor) simulator has been designed and implemented in a turbine test facility at QinetiQ Farnborough (the QinetiQ Isentropic Light Piston Facility, ILPF) to study the impact of temperature distortion on high pressure (HP) turbine efficiency, aerodynamics, and heat transfer. The ILPF is an engine scale, short duration, rotating transonic turbine test facility, in which M, Re, Tg/ Tw, and The hot-streak simulator is a second-generation design, in which cold gas is introduced into a hot mainstream though radial and circumferential slots upstream of the turbine stage. The simulator is rotatable, so the effect of clocking (relative circumferential position of hot streak and nozzle guide vane leading edge) can easily be investigated. An emphasis was placed on accurate measurement of turbine inlet enthalpy flux so that the impact of hot streaks on turbine efficiency could be investigated. The hot-streak simulator differs from all previous systems in that a pronounced radial and circumferential temperature profile has been generated, with a hot-streak to vane count of 1:1. The profile is very well matched (non-dimensionally) to the target profile, which is a combustor temperature profile measured in a modern operating engine at the most extreme point in the cycle. The most accurate area survey of a simulated temperature profile has been conducted to date, and this demonstrates that the simulator offers an exceptionally high degree of circumferential symmetry and run-to-run repeatability. The design and commissioning of the simulator is described, and the measured temperature profiles are compared with the target profile.

Clocking effect in a two-stage compressor with different inter-blade-row gaps

A multi-stage axial compressor has inherently unsteady flow fields because of the following main reasons: (1) relative positions between rotor and stator airfoil; (2) the buildup of converted wakes lead to complex wake/wake and wake/airfoil interactions. The distributions of the potential flows and wakes in the flow passage are depended on the relative positions of blade rows in axial and circumference direction, so variations in the relative axial positions (axial gap) and circumferential positions (clocking effect) of stators or rotors can change these distributions, leading to different compressor efficiency. The current study presents the experimental/numerical result of a low-speed axial compressor, considering the combined effects of stator clocking and variation of axial gaps. Testing was conducted in Two-Stage Axial Compressor Facility in Harbin Institute of Technology. In the test, time averaged data were collected. The results of experimental and time accurate flow calculation for 2 axial gaps, 8 clocking positions for each gap are compared. It is shown that clocking determines the degree of interaction of a stator with the wake of another upstream stator for different gaps between the blade rows.

Numerical Simulation of Rotor Clocking Effect in a Low-Speed Compressor

Two-dimensional (2D) unsteady numerical simulation has been applied to study the effect of the variation in relative circumferential positions of rotors on the performance of a low speed compressor. The result shows that the variation will change the relative position of upstream rotor wake to the downstream rotor as well as the periodic and turbulent velocity fluctuations on the airfoils. When the upstream rotor wake impinges upon the leading edge of the downstream rotor, the corresponding stage efficiency will be higher; when the upstream wake is transferred into the mid-passage of the downstream rotor, the corresponding stage efficiency will be lower. The proper configuration of the relative position of rotors will cause obvious reduction in the unsteady aerodynamic effect on the second rotor airfoils and improve the aerodynamic performance of blades.

Analysis of Rotor-Rotor and Stator-Stator Interferences in Multi-Stage Turbomachines

A nonlinear harmonic methodology is adopted to analyze interactions between adjacent stages in multi-stage compressors. Of particular interest are the effects of circumferential “aperiodic” distributions and the relative circumferential positioning (‘clocking’) of blades. The main feature of the present approach is that both the aperiodic and clocking effects are very efficiently included with circumferential “steady” harmonic disturbances. Consequently, a single run of the nonlinear harmonic solver using a single-passage domain can produce the whole annulus unsteady and aperiodic time-averaged flow field. In addition, performance variation at any clocking position can be obtained simply by post-processing the result. A case study is presented for a two-and-half-stage transonic compressor, and the present results show much stronger rotor-rotor interaction than stator-stator interaction. A mechanism leading to strong rotor-rotor interference seems to be the interaction between upstream rotor wakes and the downstream rotor passage shock waves. A rotor-rotor clocking study illustrates a qualitatively different loss variation with respect to clocking position in a transonic flow compared to that in a subsonic flow.

Three-Dimensional Simulations of Airfoil Clocking in a 1-1/2 Stage Turbine

Axial turbines have inherently unsteady flow fields because of the relative motion between rotor and stator airfoils. This relative motion leads to viscous and inviscid interactions between blade rows. As the number of stages increases in a turbomachine, the buildup of convected wakes can lead to progressively more complex wake/wake and wake/airfoil interactions. Variations in the relative circumferential positions of airfoils in adjacent rotating or non-rotating blade rows can change these interactions, leading to different unsteady forcing functions on airfoils and different turbine efficiencies. In addition, as the Mach number increases the interaction between blade rows can be intensified due to potential effects. It has been shown, both experimentally and computationally, that airfoil clocking can be used to improve the efficiency and reduce the unsteadiness in multiple-stage axial turbomachines with equal blade counts. While previous investigations have provided an improved understanding of the physics associated with airfoil clocking, most of the work focused on two-dimensional effects. More research is needed to determine how airfoil clocking can be incorporated in the design of three-dimensional airfoils. In the current study three-dimensional simulations of airfoil clocking have been performed for a 1-1/2 stage high-pressure turbine operating at subsonic flow conditions. Comparisons have been made with the available time-averaged experimental data at a single clocking position. The predicted results indicate approximately a 1% efficiency variation as the secondstage stator airfoils are clocked with respect to the first-stage stator airfoils. / cv Cp P P ps Pt f S ss t U a /? 7 TJ in min max ms out st tt oo 1/2 1 2 3 4 NOMENCLATURE Frequency Specific heat at constant volume (P-Pt)/(l/2pUms) Static pressure Pressure surface Total pressure Entropy Suction surface Time Rotor velocity Absolute frame flow angle (from axial) Relative frame flow angle Ratio of specific heats Efficiency Flow coefficient Density