Li Qiushi

The effect of end wall boundary layer on matching and corresponding flow control technique for multistage axial compressor

The development pattern of the end wall boundary layer (BL) in whole conditions and its effect on the matching of multistage compressor have been studied in detail in this paper. Moreover, one method of end wall zone blade modification is carried out, using computational fluid dynamics, to improve the stage matching by re-camber. It is found that the pitch-averaged thickness of end wall BL gradually increases along streamline direction and the BL is highly skewed in the pitchwise direction. In addition, the value of BL thickness, mainly depends on the stage pressure rise coefficient Δ p / ρ V x 2 . For a fixed rotating speed, the axial BL displacement thickness is changed dramatically from choked condition to near surge operating point. However, this thickness shows insensitive to the change of rotating speeds. On the other hand, BL degrades the pressure-rise characteristics of stages with low efficiency, and it results in mismatching of the compressor stage. Furthermore, the deviation angle of the blades is strongly affected by the end wall BL. Finally, two rows of stators are re-cambered on the leading edge to improve the matching near the hub region where it is influenced by end wall BL. The results show that the total pressure loss coefficient of the stators is reduced by 0.6 points and 1.73 points each. Moreover, the overall isentropic efficiency of multistage compressor is enhanced by 0.39 points without compromising pressure-rise capability and surge margin.

Application of Tandem Cascade to Design of Fan Stator with Supersonic Inflow

Abstract This article proposes a tandem cascade constructed to tackle the thorny problem of designing the high-loaded stator with a supersonic inflow and a large turning angle. The front cascade adopts a supersonic profile to reduce the shock wave intensity turning the flow into subsonic, while the rear cascade adopts a subsonic profile with a large camber offering the flow a large turning angle. It is disclosed that the losses would be minimized if the leading edge of the rear cascade lies close to the pressure side of the front cascade at a distance of 20% pitch in pitch-wise direction without either axial spacing or overlapping in axial direction. The 2D numerical test results show that, with the inflow Mach number of 1. 25 and the turning angle of 52°, the total pressure loss coefficient of the tandem cascade reaches 0. 106, and the diffusion factor 0. 745. Finally, this article has designed and simulated a high-loaded fan stage with the proposed tandem stator, which has the pressure ratio of 3. 15 and the efficiency of 86. 32% at the rotor tip speed of 495. 32 m/s.

Experimental investigation on separation control by slot jet in highly loaded compressor cascade

Separation control in compressor cascade is very significant for modern high efficiency compressor. This paper introduces a separation control approach using self-supplied jet in a highly loaded cascade. A novel arc slot is created into the cascade at the full span range, which connects the flow fields between the pressure and suction side. Because of the pressure difference, the slot enables to induce the jet flow into the suction side separation. Experiments are conducted to evaluate the separation control effects and preliminarily study the mechanism. The results show that the slot cascade acquires more ordered outflow by reducing the suction side separation and suppressing the complex vortices. Due to the great reduction of the separation, the total loss significantly decreases by 21.9% and the flow turning angle increases by 2.1° in average. According to the improvements of the cascade performance, the stable operating margin of the highly loaded cascade is greatly improved at least 3° in terms of the incidence angle.

An 11-stage axial compressor performance simulation considering the change of tip clearance in different operating conditions

The multistage axial compressor is one of the critical components of aero-engines and plays a key role in their performance, reliability, and economy. Tip clearance has a significant impact on the performance and stability of multistage axial compressors. Due to blade and disk deformations, tip clearance will vary significantly in different operating conditions. Thus, tip clearance should be accurately estimated when evaluating compressor performance. This paper proposes a new model to predict changes of tip clearance of multistage axial compressors in different operating conditions. A first-principles approach is used to estimate the change of tip clearance caused by thermal and mechanical deformation. The span-wise temperature distribution across each stage of the multistage compressors is considered by the proposed model in this paper. The model was validated by General Electric Company (GE) E3 engine experimental results. Using the model, the performance of an 11-stage axial compressor is simulated. The results show that accounting for tip clearance variations has a 0.5% impact on the calculated mass flow rate and a 1% impact on the calculated efficiency. Thus, variations of tip clearance at different operating conditions cannot be ignored and the proposed new model is useful to accurately predict the performance of multistage axial compressor.

A quasi one-dimensional bleed flow rate model for terminal normal shock stability in mixed compression supersonic inlet

Ninety-degree (normal) bleed slots have been used to stabilize the terminal normal shock in the throat of a mixed compression supersonic inlet. In this study, a quasi-one-dimensional bleed flow rate model, consisting of a constant-area channel with a pair of normal slots symmetrically located along the upper and lower endwalls, is developed. The bleed flow rate is shown to be a function of the terminal normal shock position within the slot. Some key factors, such as the bleed discharge coefficient, taken from the Bragg model, were derived from the basic laws of conservation for a one-dimensional simplification. Furthermore, numerical simulations based on Reynolds-averaged Navier–Stokes equations were performed to analyze the flow characteristics around the bleed slots. The predictions of the bleed flow rate model agree well with computational fluid dynamics results. This method may be helpful to predict the stability of the terminal normal shock in mixed compression supersonic inlets.

An Integrated Optimization Design Method Based on Surrogate Modeling Applied to Diverging Duct Design

Abstract This paper presents an integrated optimization design method in which uniform design, response surface methodology and genetic algorithm are used in combination. In detail, uniform design is used to select the experimental sampling points in the experimental domain and the system performance is evaluated by means of computational fluid dynamics to construct a database. After that, response surface methodology is employed to generate a surrogate mathematical model relating the optimization objective and the design variables. Subsequently, genetic algorithm is adopted and applied to the surrogate model to acquire the optimal solution in the case of satisfying some constraints. The method has been applied to the optimization design of an axisymmetric diverging duct, dealing with three design variables including one qualitative variable and two quantitative variables. The method of modeling and optimization design performs well in improving the duct aerodynamic performance and can be also applied to wider fields of mechanical design and seen as a useful tool for engineering designers, by reducing the design time and computation consumption.

Numerical Simulations on a Transonic Axial-Flow Compressor Rotor Under Clean and Distorted Inflows

The effects of circumferential distortions in inlet total pressure on the flow field in a low-aspect-ratio, high-speed, high-pressure-ratio, transonic compressor rotor are investigated in this paper. The flow field was studied numerically with and without inlet total pressure distortion. 3-D steady, unsteady numerical simulations have been conducted to determine the effects of circumferential total pressure inlet distortion on a transonic axial-flow compressor rotor. Overall performance (total pressure ratio, adiabatic efficiency and stable operating range) within inlet distortion has been investigated and compared with the results with clean inlet flow: dropped in mass flow, adiabatic efficiency, and decreased in surge margin. Detail analyses of the flow field in the rotor show: Circumferential flow appears at the border of the distorted region, and flows inside to the distorted region. When entering the distortion, the blade passage faces a positive pre-swirl, on the countary, when leavinging the distortion, the blade passage faces a negative pre-swirl, which increases its incidence angle and loading.