Circumferential Groove Casing Treatment Research Articles

Design optimization of a hybrid casing treatment based on axial momentum budget analysis in the tip flow region

In this paper, a novel slot–groove hybrid casing treatment is designed and optimized to improve the stall margin of a low-speed axial compressor. A combination of the axial slot and circumferential groove casing treatments is utilized to increase the stall margin without incurring efficiency loss. The slot meridional profile is described with 2 B-spline curves. Circumferential grooves are parametrically described with groove height and width. An in-house optimization design platform is constructed based on the nondominated sorting genetic algorithm II and Kriging surrogate model. The optimization objectives are the stall margin and the peak efficiency of the compressor at the design rotating speed. To avoid the large number of unsteady simulations that are required to predict the stall margin, a stall margin improvement indicator is proposed based on the axial momentum budget analysis at the rotor tip region. The performance of the optimal slot–groove hybrid casing treatment design is tested and simulated. The experimental data show that the optimal slot–groove hybrid casing treatment improves the stall margin by 8.42% without generating efficiency loss. The flow details are captured by unsteady simulations and analyzed in depth. The application of the optimal casing treatment enhances the blade tip axial momentum and the interface between tip leakage flow and incoming main flow is pushed downstream. Consequently, the stability of the compressor is improved.

Multi-Objective Optimization of Circumferential Groove Casing Treatment in an Ultra-Highly Loaded Low-Reaction Transonic Compressor Rotor

This study concerns a multi-objective optimization of circumferential single grooved casing treatment for a low-reaction transonic rotor with ultra-high loading. The axial location, width and depth of the groove are investigated as design variables. The optimization problem seeks to fully extend the operation range of the rotor while minimizing efficiency degradation. Artificial neural network of radial basis function is applied to construct the surrogate model. The optimal groove configuration was determined using non-dominated sorting genetic algorithm II (NSGA II) in conjunction with technique for order preference by similarity to ideal solution (TOPSIS). Detailed analysis of flow field reveals that two flow features involving stability enhancement for the low-reaction rotor are the inhibition of shock/vortex interaction in the rotor tip region and the reduction or elimination of double-leakage tip gap flow. The blocking region located right downstream of the interface between the tip leakage flow and the main flow is decreased due to the tip unloading effect and recirculation flow induced by the groove. Additionally, the efficiency improvement can be observed as the intensity of tip leakage vortex decreases. Based on the single groove optimization, the prospect of a particular multiple groove casing configuration consisting of component grooves with varied geometrical dimensions is also discussed in the paper. The simulation results indicate that the new-type multiple groove configuration is more advantageous to the rotor’s performance.

Axial transonic compressor performance enhancement with circumferential grooves

Abstract. Casing treatment has been broadly used as a prudent passive flow control technique to improve the stall margin with a small drop in efficiency. The effect of grooves in certain details is overlooked however, different grooves shape (angels and location) has a remarkable effect on the controlling impact. In the current research work, an investigation on the effect of fillet and chamfer corners of rectangular circumferential grooves with various tip gap height on the performance of casing treatment is carried out with the help of CFD simulation. The performance of different models of grooves with various tip gap height on NASA rotor 37 is investigated by discretizing 3D RANS equations based on finite volume technique. Rectangular circumferential grooves casing treatment (CGCT) profile and smooth wall casing performances are evaluated. Moreover, the adiabatic efficiencies and the stall margins of smooth wall casing, rectangular grooves and rectangular grooves with fillet and chamfer corners are compared to assess the impacts of profiles of grooves on the stability and performance of axial flow compressor with different tip gaps. The stall margin of models 1–6 increased by 4.39 %, 2.52 %, 2.16 %, 1.75 %, 1.69 % and 2.06 % respectively. While the adiabatic efficiency of the models 1–6 decreased by 0.9 %, 1.01 %, 1.08 %, 1.12 %, 1.22 % and 1.16 % respectively.

Performance improvement of axial compressor by introduction of circumferential grooves

ABSTRACTCasing treatment has been extensively used as a prudent passive flow control means to enhance the stall margin with a little decrease in efficiency. The shape of various grooves has a substantial influence on the controlling effect. In this study, research on the impact of rectangular, fillet and chamfer types rectangular grooves with different tip clearances gap on the performance of casing treatment is carried out using numerical simulation. The performance of different models of grooves with different tip clearance gaps on NASA rotor 37 is investigated by discretizing 3D RANS equations based on the finite volume method. A few numbers of casing grooves models are designed with various tip clearances gap and numerically tested. Rectangular circumferential grooves casing treatment (CGCT) shape and smooth wall casing performances are analyzed. Furthermore, the highest adiabatic efficiencies and stall margins of smooth wall casing, rectangular grooves and fillet, and chamfer types rectangular grooves are compared to evaluate the effect of shapes of grooves on the stability and performance of axial flow compressor with different tip gaps. The adiabatic efficiency of the models 1 ~ 6 decreased by 0.9%, 1.0%, 1.05%, 1.1%, 1.2%, and 1.15% respectively. While the stall margin is increased by 4.4%, 2.5 %, 2.2%, 1.75%, 1.7% and 2.1% for models 1 ~ 6 respectively.

Performance Enhancement of a Transonic Axial Flow Compressor with Circumferential Casing Grooves to Improve the Stall Margin

The stability range of the gas turbine engine compressors is being challenged in the modern days due to the intention of increasing per stage maximum loading. Casing treatment has been widely adopted as a realistic passive flow control means to improve the stall margin with a slight decrease of efficiency at the same time by various grooves of which shape (location, angles and so on) has a significant influence on controlling effect. However, the influence of some details in grooves is ignored in most of the case that may impact the specific flow field in the groove. A research on the impact of chamfer and fillet corners on the performance of casing treatment was proceeded by numerical simulation in this paper. The performance of different models of grooves on NASA Rotor 37 was investigated by discretizing 3D RANS based on finite volume method. Firstly, steady simulations were performed on NASA rotor 37 for validation. The CFD results and experimental data for adiabatic efficiency and pressure ratio were in good agreement. According to convergence criteria, the initiation of the stall was predicted. Few numbers of circumferential grooves casing treatment (CGCT) models have been proposed and tested numerically. Rectangular CGCT shape and smooth wall casing performances were analyzed. Moreover, the highest adiabatic efficiencies and stall margins of smooth wall casing, rectangular grooves and rectangular grooves with chamfer and fillet corners shapes models were compared to evaluate the influence of the shape of grooves on the stability and performance on axial flow compressor. The rectangular circumferential casing grooves and rectangular grooves with chamfer and fillet corners enhanced significantly stall margin and an operational range of the transonic axial flow compressor but adiabatic efficiency was slightly decreased.

Numerical Investigation of Circumferential Groove Casing Treatment in a Highly-Loaded Low-Reaction Transonic Compressor Rotor

In this paper, a computational investigation of circumferential groove casing treatment in a highly-loaded low-reaction transonic compressor rotor is conducted, in which the stage reaction is significantly reduced due to a larger meridional contraction with respect to conventional transonic compressors. Steady computation at near-stall point is performed first to capture the stall inception of the rotor with smooth casing. Detailed observations, which mainly focus on the tip leakage flow behavior, obstruction and vortical structures in the tip region, determine the reason for the compressor stall. There is tip leakage vortex breakdown in the tip region. Moreover, it yields passage obstruction, and finally leads to the compressor stall. Then, attempts are made to investigate how the circumferential grooves can be applied for the compressor’s stall margin enhancement without compromising efficiency. Three configurations are obtained and analyzed by changing axial position and the number of the circumferential grooves. The results of computational parametric study indicate the optimal location of the groove is near the leading edge and the downstream grooves combine their influence on the compressor’s stabilization and performance in a cumulative manner. The optimal circumferential groove configuration produces an increase of 1% in total pressure ratio at the near-stall point and a gain of 3.7% in stall margin, without any penalty in efficiency. Furthermore, the impact the grooves will exert on the flow mechanisms between the grooves and the main flow is also considered.

Transonic Compressor Blade Optimization Integrated With Circumferential Groove Casing Treatment

A compressor blade integrated with circumferential groove casing treatment (CGCT) is optimized in this study. A hybrid aerodynamic optimization algorithm that combines the differential evolution (DE) with a radial basis function (RBF) response surface is used for the multi-objective optimization via the computational fluid dynamics (CFD) analysis. The sweep and lean distributions are optimized to pursue the maximum total pressure ratio and adiabatic efficiency at the design point. Constraints on the choking mass flow rate and the near-stall compression ratio are imposed to ensure the off-design performance. The performance is improved much more with the blade-CGCT integrated optimization than with the blade-only optimization. The stall margin of the blade-only optimized blade with CGCT added as an afterthought can be even worse than the baseline blade. The CGCT-removal test for the blade-CGCT integrated optimization result further verifies that the superior performance of the blade-CGCT integrated optimization is obtained via optimizing the coupling between the effects of the sweep and lean on the blade loading and the effects of the CGCT on the flow blockage.

Design and Optimization of Multiple Circumferential Casing Grooves Distribution Considering Sweep and Lean Variations on the Blade Tip

This paper focuses on the design and optimization of the axial distribution of the circumferential groove casing treatment (CGCT). Effects of the axial location of multiple casing grooves on the flow structures are numerically studied. Sweep and lean variations are then introduced to the blade tip, and their influences on the grooves are discussed. The results show that the ability of the CGCT to relieve the blockage varies with the distribution of grooves, and the three-dimensional blading affects the performance of both the blade and the CGCT. Accordingly, a multi-objective optimization combining the CGCT design with the sweep and lean design is conducted. Objectives, including the total pressure ratio and the adiabatic efficiency, are set at the design point; meanwhile, the choking mass flow and the near-stall performance are constrained. The coupling between the CGCT and the blade is improved, which contributes to an optimal design point performance and a sufficient stall margin. The sweep and lean in the tip redistribute the spanwise and chordwise loading, which enhances the ability of the CGCT to improve the blade’s performance. This work shows that the present CGCT-blade integrated optimization is a practical engineering strategy to develop the working capacity and efficiency of a compressor blade while achieving the stall margin extension.

Experimental and Numerical Investigation of a Circumferential Groove Casing Treatment in a Low-Speed Axial Research Compressor at Different Tip Clearances

The demand of increasing pressure ratios for modern high pressure compressors leads to decreasing blade heights in the last stages. As tip clearances (TC) cannot be reduced to any amount and minimum values might be necessary for safety reasons, the TC ratios of the last stages can reach values notably higher than current norms. This can be intensified by a compressor running in transient operations where thermal differences can lead to further growing clearances. For decades, the detrimental effects of large clearances on an axial compressor's operating range and efficiency are known and investigated. The ability of circumferential casing grooves in the rotor casing to improve the compressor's operating range has also been in the focus of research for many years. Their simplicity and ease of installation are one reason for their continuing popularity nowadays, where advanced methods to increase the operating range of an axial compressor are known. In the authors' previous paper, three different circumferential groove casing treatments were investigated in a single-stage environment in the low-speed axial research compressor at TU Dresden. One of these grooves was able to notably improve the operating range and the efficiency of the single stage compressor at very large rotor TC (5% of chord length). In this paper, the results of tests with this particular groove type in a three stage environment in the low-speed axial research compressor are presented. Two different rotor TC sizes of 1.2% and 5% of tip chord length were investigated. At the small TC, the grooves are almost neutral. Only small reductions in total pressure ratio and efficiency compared to the solid wall can be observed. If the compressor runs with large TC, it notably benefits from the casing grooves. Both, total pressure and efficiency can be improved by the grooves in a similar extent as in single stage tests. Five-hole probe measurements and unsteady wall pressure measurements show the influence of the groove on the flow field. With the help of numerical investigations, the different behavior of the grooves at the two TC sizes will be discussed.

Study on casing treatment and stator matching on multistage fan

Casing treatments are required for expanding the stall margin of multi-stage high-load turbofans designed with high blade-tip Mach numbers and high leakage flow. In the case of a low mass flow, the casing treatment effectively reduces the blockages caused by the leakage flow and enlarges the stall margin. However, in the case of a high mass flow, the casing treatment affects the overall flow capacity of the fan, the thrust when operating at the high speeds usually required by design-point specifications. Herein, we study a two-stage high-load fan with three-dimensional numerical simulations. We use the simulation results to propose a scheme that enlarges the stall margin of multistage high-load fans without sacrificing the flow capacity when operating with a large mass flow. Furthermore, a circumferential groove casing treatment is used and adjustments are made to the upstream stator angle to match the casing treatment. The stall margin is thus increased to 16.3%, with no reduction in the maximum mass flow rate or the design thrust performance.

Numerical analysis of flow in a centrifugal compressor with circumferential grooves: influence of groove location and number on flow instability

As an effective and economic method for flow range enhancement, circumferential groove casing treatment (CGCT) is widely used to increase the stall margin of compressors. Different from traditional grooved casing treatments, in which the grooves are always located over the rotor in both axial and radial compressors, one or several circumferential grooves are located along the shroud side of the diffuser passage in this paper. Numerical investigations were conducted to predict the performance of a low flow rate centrifugal compressor with CGCT in diffuser. Computational fluid dynamics (CFD) analysis is performed under stage environment in order to find the optimum location of the circumferential casing groove in consideration of stall margin enhancement and efficiency gain at design point, and the impact of groove number to the effect of this grooved casing treatment configuration in enhancing the stall margin of the compressor stage is studied. The results indicate that the centrifugal compressor with circumferential groove in vaned diffuser can obtain obvious improvement in the stall margin with sacrificing design efficiency a little. Efforts were made to study blade level flow mechanisms to determine how the CGCT impacts the compressor’s stall margin (SM) and performance. The flow structures in the passage, the tip gap, and the grooves as well as their mutual interactions were plotted and analysed.

Axial Compressor Stall, Circumferential Groove Casing Treatment, and the Tip-Clearance Momentum Flux

The stall margin and pressure ratio of an axial compressor can both be increased with the use of circumferential groove casing treatments over the rotor. Performance and stall point measurements were obtained in a single-stage high-speed axial compressor with seven different casing treatment configurations. The different configurations were designed to investigate the effects of the number and placement of circumferential grooves. The results demonstrated that the stall margin extension caused by individual grooves could be added together to obtain the value obtained with the equivalent multigroove configuration. Furthermore, the relationship between stall margin extension and the tip-clearance momentum flux was considered. A Reynolds-averaged Navier–Stokes computational solution from the smooth-wall configuration was used to obtain the momentum flux of the reverse flow at the tip. The results showed a linear relationship between the measured stall extension and the computed smooth-wall momentum flux integrated over the region occupied by the grooves.

Investigation of Performance and Rotor Tip Flow Field in a Low Speed Research Compressor with Circumferential Groove Casing Treatment at Varying Tip Clearance

Experimental investigations in a single-stage low speed axial research compressor are presented. The influence of four different rotor tip clearances on the overall compressor performance and on the rotor tip flow field is investigated in configurations with and without circumferential groove casing treatments. Piezo-resistive pressure transducers are used to capture the unsteady flow field in the rotor tip region. The investigated casing groove is effectively working at the three largest investigated tip clearance sizes. The largest achieved operating range increase by the groove is 6.9%. The groove can delay the upstream movement of the flow interface between leakage flow and main flow and thus increase the stable operating range. Rotating instabilities are shown to exist at large tip clearance sizes in throttled operating conditions. Their amplitudes can be damped by the casing groove. No modal activities could be detected in the current single-stage compressor build.

Numerical Study on the Effect of Single Shallow Circumferential Groove Casing Treatment on the Flow Field and the Stability of a Transonic Compressor

The present research investigates the effect of the location and the width of single shallow circumferential groove casing treatment on the flow field and the stability improvement of NASA Rotor 37 utilizing the help of computational fluid dynamics. At first, steady state simulation of Rotor37 was presented for smooth casing (without groove). Then, forty five various grooved casing were simulated and compared with the smooth casing. The results indicated that narrow grooves had slight effect on the adiabatic efficiency but as the width of the groove was increased, a decline in efficiency was observed. The investigation on the stall margin revealed that narrow grooves next to the leading edge could improve the stall margin by a reduction in the size of vortex breakdown zone. Medium-width grooves displayed an effective role in delaying the separation- produced by shock wave and boundary layer interaction- on the blade suction side near the casing. This type of grooves could improve the stall margin more than narrow grooves when located on the top of separation zone near the blade suction side. Wide grooves had negative effect on the stall margin and caused a significant drop in the efficiency and the total pressure ratio of the compressor.

The stall inceptions in an axial compressor with single circumferential groove casing treatment at different axial locations

Circumferential groove (CG) casing treatment is known to be a good method to improve the stall margin of axial compressor. Recent studies on single groove indicate the stall margin improvement (SMI) is significantly affected by groove's axial location, which means the effects of the groove on the passage flow should be further studied as the groove's axial location is changed. In this paper the features of stall inception with and without the groove treatment are experimentally researched in a low-speed axial compressor. The contour of static pressure on casing is obtained by fast-response pressure transducers concentrative mounted as a line in chordwise direction, and the data acquired by transducers in circumferential direction is processed with the method of wavelet analysis to demonstrate the development of stall inception. It is found the stall inception is the typically spike-type for smooth casing (without treatment), which is manifested as short-scaled disturbance of only 2–4 blade passages when it appears. Two single grooves at different axial locations, which can be ineffective and effective in SMI, are further tested. The results indicate the stall inception is still spike-type for both of them. However, for the ineffective groove, the stall inception is found to be relatively longer-scaled disturbance. For the effective groove, it is still the typical short-scaled disturbance similar to the smooth casing. In the further study on double grooves treatment in which the ineffective groove is included, the stall inception is also found to be relatively longer-scaled type. According to these experimental results and previous CFD simulation, the groove with almost no SMI is believed to take different effects on the compressor which modifies the stall inception into the relatively longer-scaled type, and the corresponding tip–region flow structure deserves more future study in this regard.

Investigation of groove casing treatment in a transonic compressor at different speeds with control volume method

This article uses a control volume method to analyze the circumferential groove casing treatment in a transonic compressor. To analyze the axial momentum transport through the tip gap, the control volume near the casing is divided into two parts: the control volumes inside and outside the tip gap. Besides, the association between the forces acting on the control volume and flow structures is studied by analyzing the distributions of axial momentum flux and axial shear stress. With this method, the flow mechanisms of stall margin improvement due to casing grooves in Rotor 35 are quantitatively analyzed. The analysis is conducted at 100% and 60% design speed with supersonic and subsonic tip speed, respectively. At design speed, the casing grooves decrease the axial shear force and the axial force due to the transport of axial momentum induced by the tip leakage flow. Meanwhile, the bleeding and injecting effect of grooves contribute much to the axial force due to the transport of axial momentum. Based on the axial distribution of the axial forces, the contribution of each groove to the stall margin improvement is assessed. And the grooves that play a major role in stall margin improvement are ascertained. At 60% design speed, because the blade loading is reduced, the axial momentum transport caused by the grooves cannot suppress the boundary layer separation effectively. Consequently, the stall margin of the compressor is not significantly improved by the casing grooves.

Numerical investigation of a centrifugal compressor with circumferential grooves in vane diffuser

Enhancing stall and surge margin has a great importance for the development of turbo compressors. The application of casing treatment is an effective measure to expand the stall margin and stable operation range. Numerical investigations were conducted to predict the performance of a low flow rate centrifugal compressor with circumferential groove casing treatment in vane diffuser. Numerical cases with different radial location, radial width and axial depth of a circumferential single groove and different numbers of circumferential grooves were carried out to compare the results. The CFD analyses results show that the centrifugal compressor with circumferential grooves in diffuser can extend stable range by about 9% while the efficiency over the whole operating range decreases by 0.2 to 1.7%. The evaluation based on stall margin improvement showed the optimal position for the groove to be located was indicated to exist near the leading edge of the diffuser, and a combination of position, width, depth and numbers of circumferential grooves that will maximize both surge margin range and efficiency.

A Computational Fluid Dynamics Study of Circumferential Groove Casing Treatment in a Transonic Axial Compressor

Numerical investigations were conducted to predict the performance of a transonic axial compressor rotor with circumferential groove casing treatment. The Notre Dame Transonic Axial Compressor (ND-TAC) was simulated at Tsinghua University with an in-house computational fluid dynamics (CFD) code (NSAWET) for this work. Experimental data from the ND-TAC were used to define the geometry, boundary conditions, and data sampling method for the numerical simulation. These efforts, combined with several unique simulation approaches, such as nonmatched grid boundary technology to treat the periodic boundaries and interfaces between groove grids and the passage grid, resulted in good agreement between the numerical and experimental results for overall compressor performance and radial profiles of exit total pressure. Efforts were made to study blade level flow mechanisms to determine how the casing treatment impacts the compressor's stall margin and performance. The flow structures in the passage, the tip gap, and the grooves as well as their mutual interactions were plotted and analyzed. The flow and momentum transport across the tip gap in the smooth wall and the casing treatment configurations were quantitatively compared.

Numerical investigation of the casing treatment mechanism with a single circumferential groove

The paper investigates the effect of a single circumferential groove casing treatment (CGCT) on a transonic compressor rotor numerically. In particular, the effect of the groove at different axial locations on the flow field is studied in detail and stall margin improvement is also discussed. The present results show that the groove close to the leading edge plays a crucial role in stabilizing the near stall flow structures and, hence, improves the stall margin. The groove at the mid-chord-section of the blade can help exchange and transfer momentums between different directions, and suppress the flow unsteadiness, leading to increased efficiency in rotor performance and extended operation range. The groove located near the blade trailing edge has limited effects on stall margin improvement and may cause additional penalty in efficiency. Through comparison with the recent work on CGCT, some common flow physics can be observed.

Multiobjective Optimization of Circumferential Casing Grooves for a Transonic Axial Compressor

R ECENTLY, casing treatments using grooves or slots have been applied to axial compressors to prevent surge and enhance stall margin (SM). However, this is accompanied by a loss near the blade tip region, which leads to a decrease in efficiency of the axial compressor. Therefore, a systematic design of the casing treatment using multiobjective optimization techniques in conjunction with a flow analysis using three-dimensional Reynolds-averaged Navier– Stokes equations (RANS) was used to investigate a compromise between the SM and the efficiency of the compressor. Various types of grooves have been suggested by many researchers, and it has been reported that using grooves increases SM by delaying stall. Huang et al. [1] studied the effects of the configuration, width, and depth of circumferential groove casing treatment on SMby numerical analysis, and suggested that the stall mechanism was substantially influenced by tip clearance.Muller et al. [2] studied the effects of the number and depth of the grooves on SM by threedimensional numerical analysis. Houghton and Day [3] examined the effect of grooves on rotor outflow blockage, and the near casing flowfield was studied using experimental and computational methods. Many engineering designs involve multiple disciplines and simultaneous optimization of multiple objectives related to each discipline. These design problems, usually known as multiobjective problems, require simultaneous consideration of all objective functions to optimize the system. The nondominated sorting genetic algorithm (NSGA-2) by Deb [4] generates a Pareto-optimal solution using an evolutionary algorithm. Shape optimization of a hydraulic turbine diffuser was performed with multiple objectives by Marjavaara et al. [5]. Kim et al. [6] reported a multiobjective optimization of a centrifugal compressor impeller with four design variables that defined the impeller hub and shroud contours in meridian terms. Samad and Kim [7] reviewed the performance of the surrogate models applied to turbomachinery design optimization, and introducedmulti and single-objective optimization techniques in conjunction with three-dimensional RANS analysis. In this study, based on previous work [8] for a single-objective optimization, a hybridmultiobjective evolutionary algorithm (hybrid MOEA) [9] coupledwith the Kriging (KRG)model [10] was applied to obtain a global Pareto-optimal front for the design of circumferential casing grooves in an axial compressor with NASARotor 37 [11]. To the best of the authors’ knowledge, no previous study has reported on the optimization of the design of circumferential casing grooves. The present multiobjective optimization was motivated to provide an efficient tool for the design of an axial compressor with circumferential casing groove treatment, and it is expected for designers to meet their design requirements with regard to the SM and adiabatic efficiency from the Pareto-optimal designs (PODs) obtained in this work. Numerical solutions at the selected design points were obtained by three-dimensional RANS analysis. The shape of the grooves was optimized by considering width and depth as designvariables in order to improve the SM and the peak adiabatic efficiency. The tradeoff between these two competing objective functions is explored and discussed with respect to the design variables.