A Method of Bending Shrinkage Groove on Vortex Suppression and Energy Improvement for a Hydrofoil with Tip Gap

Hydro energy is a kind of typical renewable energy, which can be converted by hydraulic machinery. However, tip leakage vortex (TLV) has a significant negative influence on the flow pattern and energy performance of hydraulic machinery. In this paper, a bending shrinkage groove (BSG) is proposed to suppress the TLV and improve the energy performance of a hydrofoil first, and then a parametric optimization design method is briefly introduced and applied to determine the optimal configuration of the groove. The main geometric parameters of the groove are selected as optimized variables and three different groove configurations are selected from the optimization result. Finally, the performance improvement of the hydrofoil with groove, the sensitivity analysis of the optimization variables, and the groove impacts on the TLV and flow patterns are investigated. The results demonstrate that the preferred groove reduces the non-dimensional Q criterion vortex isosurfaces area (Qarea = 2 × 107) by 5.13% and increases the lift drag ratio by 17.02%, comparing to the origin hydrofoil. Groove depth d and groove width w are proved to have more significant impacts on the hydrofoil energy performance. The TLV and flow patterns are greatly affected by the different BSG configurations, and the wider BSG contributed to reducing the area of TLV, at the cost of energy performance deterioration.

Numerical investigation of particle trapping in various groove configurations in straight and bent flow channels

A novel computational technique is applied to investigate particle trapping in straight and bent channel flow paths with various groove configurations in high-speed compressible, particle laden flow. The technique is valid for particle sizes of the same order of magnitude as the groove dimensions and where the particle–flow path, particle–particle, and particle–flow interactions play significant roles in determining the particle motion. The sacrificial grooves within the flow path can remove particles from the flow to reduce particle impact-induced wear. The feasibility of the trapping grooves and the conditions for which they are most beneficial can be gleaned from analysis of the model results. Three groove configurations are studied: a straight groove, a flared groove, and a 45 degree angle groove, for the same groove entrance size, groove depth, and spacing in a straight channel and a channel with a 90 degree bend. A transient maximum of 22% of the particles were trapped for the flared groove for the bent channel and a transient maximum of 15% of the particles for the straight channel configuration. The second groove of the bent channel produces the greatest single groove particle holding of 8.25% of all of the particles for the flared grove configuration. The contributions of the groove positioning, groove shape, gas flow, and particle interaction conditions to the trapping characteristics can be readily obtained from examination of the model results since the modeling technique includes detailed treatment of particle–flow path and flow interactions, allowing for the study of the mechanisms acting to trap the particles within the grooves.

Experimental Investigation of Circumferential Groove Casing Treatments for Large Tip Clearances in a Low Speed Axial Research Compressor

In high pressure compressors large tip clearances can occur in the rear stages especially during transient operation. This can lead to a reduced operating range and performance of the compressor. One simple means to reduce the negative effects of a rotor tip clearance increase can be circumferential groove casing treatments. Their ability to improve the operating range of a compressor is well-known for several decades. In this paper, an experimental study to investigate the influence of three different circumferential groove casing treatments on a low speed axial research compressor with very large rotor tip clearances (5% of annulus height) is presented. Two single-groove and one double-groove casing treatments have been tested. The grooves are positioned from 31% to 69% axial chord. The compressor characteristics of the smooth wall and the three groove configurations are discussed as well as selected five-hole probe measurements of the flow field downstream the rotor. It can be shown that all grooves are able to improve the operating range of the compressor. Furthermore, an improvement of efficiency due to the casing grooves can also be observed in certain operating points.

The Analysis of Axial Momentum of the Rotor Tip Flows for Axial Compressors With Circumferential Grooves

A new control volume analysis is developed in this paper aiming at assessing the circumferential grooves effectiveness on stability improvement. The underlying mechanism for this approach is based on the hypothesis that the spike stall precursors can be triggered by the forward spillage of the rotor tip leakage flow and the onset condition of such a spillage is determined by the axial momentum balance within the rotor tip region. Control volumes are defined to quantify the axial momentum balance of the whole region where the grooves influence the flow at the rotor tip. The distribution curve of the cumulative axial momentum along the axial chord indicates that the grooves change the rotor tip loading and increase the stability, which is useful to assess the different grooved casings. As an example, multiple-groove configurations for a transonic rotor are analyzed. The results verified the cumulative axial momentum distribution for different grooved casings are in accordance with the stall margin extension variations. Another example is to prescreen the best double-groove configurations for a low speed compressor. By using this current approach, a double-groove configuration was selected and validated by experiments. These examples demonstrate the current approach has great potential in helping pre-screen circumferential grooves. As an important issue, peak efficiency changed by the grooves is discussed in the last section. Entropy production is quantitatively compared with and without grooves.

Investigation of Design Features of Compressor Casing Treatment

Casing treatment in the form of circumferential grooves over a rotor blade tips is used for improvement of an axial compressor performance. Usually, these grooves extend compressor’s stall range (stable operational range) but decrease its efficiency. In the paper, there are presented main results of investigations on grooves that influence positively efficiency of compressor. There were investigated traditional (typical) and newly developed groove configurations. Certain grooves combine increase in efficiency with extension in stall range.