Abstract The performance and stability of aero-gas turbine engines are heavily dependent on the compressor, which is the key component for pressure increase. Therefore, it is crucial to effectively evaluate and analyze the off-design point performance and stability of the compressor with clean and distorted inlet conditions during the engine development process. This paper takes the basic idea of Koch’s maximum static pressure coefficient method as the research foundation, and through the analysis and summary of a series of experiments, it proposes a method for determining the stable boundary of an axial compressor in the case of inlet swirl distortion, filling the gap of the lack of a corresponding stable boundary determination method for multistage introduction.

For multi-shaft aero-engines, the downstream compressor inlet will be exposed to rotating inlet distortion once rotating stall occurs in the upstream fan or low-pressure compressor. In this paper, an experimental study is carried out on six axial compressors under rotating inlet distortion, aiming to clarify the effects of rotating inlet distortion and reveal the stall mechanism. The result under rotating inlet distortion shows that the rotational speed of distortion strongly affects the stability of the compressor. Within a certain band of distortion speeds, i.e., in the dangerous distortion speed band, the stability margin of the compressor decreases extremely severely. Comparing the results from the six compressors, it is discovered that the left boundary of the dangerous distortion speed bond coincides with the propagation speed of rotating stall, whereas the right boundary is associated with the distortion angle. When introduced rotating inlet distortion, flow separation is prone to occur in the high-load region, which consequently induces stall disturbance. The reason for the varying stability margin with the distortion speed is that the distortion zone at different speeds affects the spatiotemporal evolution of the stall disturbance. Within the dangerous distortion speed bond, the intensified effect of the distortion zone accelerates the evolution of stall disturbance into rotating stall. At the end of this paper, a model is proposed to explain the impact of distortion speed and distortion angle on compressor stall.

According to Emmons's classic theory, compressor stall is triggered by high incidence in one certain blade passage and its propagation is driven by flow diversion toward adjacent passages. In this theory, blades are assumed to be axisymmetric around the annulus. In practice, the assembly usually causes the non-axisymmetric distribution of the blades. The focus of this paper is to answer how mistuned blades affect stall inception and whether even can mitigate its propagation. This paper conducts detailed unsteady measurements on an axial compressor with mistuned rotor blades, where the stagger angle is of the priority of blades mistuning. The results indicate that blade loading around the annulus varies and correlates obviously with the stagger angle. Owing to the difference in blade loading, the flow in three specific blades (with higher stagger angle) shows less unsteadiness, compared to that of other blade passages. For the base configuration (the error of stagger angle within 1°), stall inception revolution does not show any difference. Of interest, when the error increases to 4°, disturbances surprisingly occur and propagate around the annulus at the stable operation condition near the stall boundary, which is triggered by the mistuned blade and will decay within one revolution in the rotor frame of reference. The phenomenon demonstrates the suppression effect of other blades with changed stagger angle on the propagation of stall inception. With the compressor throttled further, full rotating stall eventually occurs once disturbances can propagate around the entire annulus. Therefore, the aerodynamic mistuning has a clear effect on the stall inception and propagation, which can be further discovered for the stall control and stability design.

A quantitative model to predict the boundary of instability of axial compressors based on their maximum loading capability is proposed in this paper, which is an improved version of the classic method of stalling pressure rise. The original model correlates the maximum pressure rise of a compressor to a characteristic geometric parameter, which is an analogue of the normalized length of diffusion in two-dimensional diffusers. However, the influence of the aspect ratio of the passage is overlooked in this analogy, which leads to significant discrepancies in its predictions for compressors, especially those with varying blade aspect ratios. Our model contains two improvements to address this issue. The first involves refining in the definition of the normalized length of diffusion, whereas the second introduces a supplementary correction factor for the aspect ratio of the blades. Nearly 20 low-speed compressor configurations, with variations in solidity, aspect ratio, tip clearance, and axial spacing, were tested to develop the proposed model. It can reduce error in the predicted stalling static pressure rise from 10% to 5%. Experimental data robustly verify the accuracy of our model, making it a more reliable predictive tool of instability boundary in the preliminary design of axial compressors.

A parametric experimental study was conducted to determine the aerodynamic effects of solidity on low-speed axial compressors. The results show that total pressure ratio and efficiency vary monotonically with solidity, and interestingly the influencing trend reverses progressively with the compressor throttling to the stall boundary. It is supported by the five-hole probe traverse, which demonstrates the blockage is generally reduced with the increasing solidity near the stall boundary, and vise verse for the peak efficiency point. Also, the relation between stalling static-pressure-rise coefficient and normalized diffusion length was presented and compared with the data in the previously-published literature. An unexpectedly great agreement with the correlation is shown, which convincingly confirms its effective application in predicating the compressor boundary as a simplified approach. And unsteady transducers are employed to measure rotor tip flow, the results of which indicate there exists more complex mechanism of prestall disturbances needed to be studied further.

In this paper, a method for simulating the instability transient process of the axial compression system based on the body-force model is developed, and a corresponding simulation program is developed. Simulations of the transient process of instability were carried out on a high-speed four-stage compressor and compared with experimental data. At 50% of the design rotational speed, the type of instability was rotating stall, and the simulated and experimental stall cell propagation speed were very close to each other. At 70% of the design rotational speed, the type of instability was surge. A “surge loop” was simulated, and the surge period and the percentage of time spent in each phase were consistent with the experiments. The simulation successfully predicted the blockage in the surge re-pressurization phase, proving the reliability of the simulation results. In addition, the computation yields more information about the flow field. By summing the blade forces of all grids on a blade row by volume, the surge loadings are obtained. The analysis of the axial momentum equation shows that the obtained blade force variations are reasonable. The simulation time of the multistage axial compressor is greatly reduced compared to the full annulus three-dimensional unsteady Reynolds-averaged Navier–Stokes method, demonstrating its great advantage in the design phase of the compressor.

The complete operating range of the compressor includes stable and unstable conditions, and the boundary between the two is the stall and surge line. Previously, the two were modeled in isolation from each other. The unsteady flow equation of the compression system is constructed based on the idea of the body-force model. It is possible to obtain the steady characteristics and transient simulation of post-stall, realizing the unified simulation of the full working conditions of the compression system. Among them, by using and developing the elementary cascade method, the continuity of correlation method for the body-force source term in different flow regions is realized. The model was validated on four single-stage compressors as well as one two-stage compressor, and the results showed that the steady-state characteristics, stable boundary, and rotating stall characteristics obtained by the developed model were in good agreement with the experimental results. The experiments showed that when the blade solidity was increased, the compressor's work capacity increased and its stability improved, and the rotational frequency of the stall cell increased slightly. The calculated results always agreed with the trend of the experimental results. In addition, the variation of blade forces during rotating stall can be easily obtained using the concept of body force and more details of the flow field can be obtained using the model.

Despite the extensive application of three-dimensional Reynolds-averaged Navier-Stokes equation (RANS) in axial compressor numerical simulations, body-force model (BFM) also plays its own role profiting from its low computation cost. However, the computation accuracy highly depends on the modeling of blade force, which usually involves several parameter constants. In this work, data assimilation based on Ensemble Kalman Filter (EnKF) was employed to optimize these model constants in BFM. Previous work associated with data assimilation mainly focuses on employing only one data source. Considering the various measurement quantities in engineering practice, disparate data were incorporated into the assimilation method to improve the prediction. The test case of a low-speed axial compressor was provided. Only one single data source, i.e., total pressure ratio, was first employed as the observation data in EnKF. And to reveal the superiority of the disparate data assimilation, total pressure ratio and isentropic efficiency were then incorporated to improve the performance prediction. The converged results reveal the robustness of disparate data assimilation based on EnKF. At last, the rationality of the optimized constants is verified further through the great agreement between the measurement and the prediction of BFM, with regard to the radial profile and the performance at another rotational speed.

To make measurement of end-wall flow between blade rows in a compact multistage configuration possible, a miniature L-shaped five-hole probe was employed in this paper. This compact tip structure, realized by laser-printing instead of the conventional machining technique, reduces the blockage effect of this intrusive measurement on the flow and ensures high spatial resolution. The zonal method is introduced to extend the usable flow angle range up to 60 degrees. A local least-squares interpolation technique is utilized to acquire flow angle and static/total pressure. In order to improve accuracy for the points located at the sector boundary, the overlap region method is included in the interpolation. Additional test data indicate that the maximum error in flow angle is nearly within 1 degree, and the maximum errors of total pressure and static pressure are 0.56% and 1.9% respectively. The application in a low-speed multistage axial compressor indicates that the zonal method can decrease the number of points exceeding the measurable flow range and is of great significance for the end-wall flow measurement, especially for the near-stall condition. Compared with the traditional method, the proportion of available data for the near-stall state measurement was increased by 18% by using the zonal method.

The distorted inlet flow that is a widespread flow phenomenon in compressors not only reduces the compressor performance but more seriously deteriorates the compressor stability, thus threatening flight safety. However, quantitatively determining the stability boundary is challenging due to the complexity of the distorted inlet flow. The effective static-pressure-rise coefficient in the stability criterion from Koch, a stability analysis method under clean inlet flow, was applied to explore the compressor stability under circumferential total pressure distortion. Using a series of single-stage axial compressor experiments for aspect ratio and solidity, this study investigated the influence of the distortion index on compressor stability. Subsequently, based on the analysis method under clean inlet flow, a new stability criterion under circumferential total pressure distortion was established to determine quantitatively the stability boundary. In addition, the stability criterion for determining the stability boundary was combined with the body force model for calculating the compressor performance to simulate a five-stage axial compressor under 120 & DEG; total pressure distortion, and the results were in agreement with the experimental data to verify the stability criterion. Numerical simulation was used to show the internal flow field in the compressor, analyze the load at each stage, and identify the instability stage that induces stall, which can provide a reasonable solution for determining the stability boundary of a multistage axial compressor under circumferential total pressure distortion. The combination can serve as a convenient preliminary design tool to evaluate compressor stability using fewer computational resources.

Abstract This paper applies a body force model developed recently to investigate the interaction between total temperature distortion and a multistage fan. The off-design performance of the fan shows the reasonable predicting accuracy and supports the present model is applicable for high-speed multistage machines. The transfer behaviors of 90° steady-state circumferential total temperature distortion as well as combined total pressure and total temperature distortion in the multistage environment are captured successfully by the model. The mechanism of the phase shift of the high temperature sector is discussed by the model to advance the understanding of the total temperature distortion problem. The results reveal that the large-scale flow feature of total temperature distortion in the multistage environment can be capably quantified by the present body force model with the acceptable computational consumption.

Objective: To explore the association between vitamin A (vit A) status and risk of asthma.Methods: PubMed, Web of Science, Embase and the Cochrane Library were electronically searched to identify related studies that reported the association between vit A status and asthma. All databases were searched from inception to November 2022. Two reviewers independently screened literature, extracted data, and assessed risk bias of included studies. Meta-analysis was performed on R software Version 4.1.2 and STATA Version 12.0.Results: A total of 19 observational studies were included. A pooled analysis showed that the serum vit A concentrations in patients with asthma was lower than that in healthy controls (standard mean difference (SMD)= −2.479, 95% confidence interval (CI): −3.719, −.239, 95% prediction interval (PI): −7.510, 2.552), and relatively higher vit A intake in pregnancy was associated with an increased risk of asthma at age 7 years (risk ratio (RR)= 1.181, 95% CI: 1.048, 1.331). No significant correlation was observed between serum vit A levels or vit A intake and the risk of asthma.Conclusion: Our meta-analysis confirms that serum vit A levels are lower in patients with asthma than in healthy controls. Relatively higher vit A intake during pregnancy is associated with an increased risk of asthma at age 7 years. There is no significant correlation between vit A intake and asthma risk in children, nor between serum vit A levels and asthma risk. The effect of vit A may depend on age or developmental stage, diet and genetics. Therefore, further studies are needed to explore the association of vit A and asthma.Systematic Review Registration:https://www.crd.york.ac.uk/prospero/CRD42022358930, identifier CRD42022358930

Background. Intervertebral disc degeneration (IDD) refers to intractable pain in patients’ waist and legs, which is caused by internal structural disorder and degeneration of intervertebral. This disease severely affects the quality-of-life of people. It has been reported that hydroxysafflor yellow A (HSYA), the active ingredient in safflower extract, could inhibit IL-1β-induced apoptosis of endplate chondrocytes. However, the mechanism by which HSYA regulates the occurrence and progression of IDD remains unclear. Methods. Rat endplate chondrocytes were isolated from the intervertebral disc. Next, toluidine blue staining and collagen II immunofluorescence staining were used to identify endplate chondrocytes. Then, MDC staining was used to detect the autophagy of endplate chondrocytes. In addition, Western blot was used to measure the expression of cleaved caspase 3, LC-3I/II and ATG7 in endplate chondrocytes. Results. IL-1β obviously inhibited the viability and proliferation of endplate chondrocytes, while these phenomena were notably reversed by HSYA. Additionally, HSYA was able to inhibit IL-1β-induced apoptosis of endplate chondrocytes. Moreover, HSYA protected endplate chondrocytes against IL-1β-induced inflammation via inducing autophagy. Conclusion. HSYA protected rat endplate chondrocytes against IL-1β-induced injury via promoting autophagy. Therefore, the present study might provide some theoretical basis for exploring novel and effective methods for patients with IDD.

The onset of rotating stall and surge in compressors limits the operating range of aero-engines. Accurately predicting the key features during these events is critical in the engine design process. In this paper, a three-dimensional computational model for transient simulation of multi-stage axial compressors during stall is proposed. The kinetic equations describing the dynamic process of the compression system are constructed, with a 3D through-flow model for the compression part and a 1D gas collector model for the outlet part. The calculation of the source term is performed using the developed body-force model, which realizes the correlation between the deviation angle and the loss coefficient with the inlet parameters in various flow regions. Validated on a single-stage compressor and a single-rotor fan, the results show that the method is capable of capturing the stall and surge features correctly and that the three-dimensional structure of the stall cell can be captured. In addition, this model could be used for the analysis of the surge load, which is significant for the structural integrity of the compressor.

At the requirements level, formal verification and analysis are the focus of task’s attention which is developing complex systems by formal methods. Model checking is a technique for analysis and automated verification of complex safety-critical software systems. In this paper, a requirement model verification method based on formal technology is proposed to practice the model checking activity into the development process. Firstly, this essay analyzes syntax and semantics of models, which are defined by tabular expressions in VRM (variables relationship model). Then we preprocess the VRM model to classify into events tables, conditions tables and model class tables, and transform the VRM model into the automaton state transfer diagram with the help of semantic complementary work. Finally, we design an automatic model transformation framework from the VRM model to the model verification tool (nuXmv) and implement a translator between the formal specification language VRM and the symbolic model checker nuXmv. In this paper, we discuss our translation and abstraction approach in some depth and illustrate its feasibility with some preliminary examples.

In this paper, the single-stage compressor with circumferential non-uniform tip clearance is experimentally investigated under 180° total pressure distortion for the compressor characteristics and the dynamic stall process. In the special structure of the circumferential non-uniform tip clearance, different circumferential distortion areas are adopted to actively induce the stall. The maximum or minimum flow coefficient near the stall point occurs when the location where the rotor departs the distortion area is at the average tip clearance rather than the maximum or minimum tip clearance. Based on the time-frequency analysis regarding the dynamic stall process at different correspondences between the inlet distortion and the tip clearance, it is found that the rotating frequency of the stall cell that is independent of the location of the distortion area is slightly less than 50% rotor rotating frequency and the large-scale stall inception whose frequency is 4–8 times the rotor rotating frequency occurs. Besides the circumferential phase difference from 90° to 180° between the location where the disturbance occurs and the location where the rotor departs, the distortion area exists. According to the dynamic stall process, the stall interpretation model of circumferential total pressure distortion under the circumferential non-uniform tip clearance is established.

AltaRica 3.0 is a high-level modeling language for safety critical systems, which can be used for system modeling and safety analysis. At present, there are some tools for AltaRica 3.0, such as OpenAltaRica, which can realize system modeling and step simulaiton. However, they can’t support graphical modeling and display. Therefore, this paper aims to design and implement a modeling and simulation tool with graphical modeling function based on AltaRica 3.0. The main work includes the following aspects: Firstly, a text editor for modeling is constructed. Fault model compilation, fault tree generation and fault tree analysis are implemented based on OpenAltaRica’s engines and Arbre Analyste tool. Secondly, a graph editor is constructed, and the functions of loading, modifying and saving graph models are realized. Then, a simulation method based on step simulation engine is designed and implemented. Finally, the correctness and effectiveness of the modeling and simulation method are verified through the analysis of an example system.

Airborne software systems play very important roles in modern civil aircraft systems, and there are several safety standards, including DO-178B/C, etc., that are compulsory to be satisfied before airborne software can be certificated by the authority of government. According to the DO-178B/C, the consistency and integrity of airborne software requirements must be analyzed and verified in the early stage of software development. In this paper, we introduce a formal modeling and analysis tool platform (ART: Avionics Requirement Tools) for airborne software natural language requirements, and a case study of the requirements of the software subsystem of the Indication-Recording System (IRS) is provided. Firstly, we give the semantics of a formal Variable Relationship Model (VRM), the platform architecture, and toolchain of ART. Then a methodology of formal analysis of requirement consistency and integrity based on a multi-paradigm is given. After that, some details of the case study of IRS are shown including: how to make a preproccessing of original requirements and the automatic analysis process of the requirement model, such as the preprocessing and standardization of original requirement items, automatic generation of VRM models and multi-paradigm based formal analysis, etc. Lastly, some experiences of this case study are shown.

对低速轴流单级使用数值模拟的方法,研究靠近稳定边界处,压气机内详细的流场结构.对于不同叶高,随着叶片高度增加,叶片的压差越大,负荷越大.对转子前缘的压力数值探针结果进行傅里叶分析且表明,转子周向上出现了两种不同旋转周期的静压扰动,分析不同周向点的压力结果,呈现的扰动现象不同.由于叶尖间隙的存在,产生了叶尖泄漏涡,并且与主流相互作用,不同周向位置的涡系结构存在区别.对于该压气机,在近失速点附近,质量流量过小,产生的泄漏涡强度有限,最终未出现经典的旋转不稳定现象,反而更接近于叶顶自激励非定常.