Impacts of tandem configurations on the aerodynamic performance of an axial supersonic through-flow fan cascade

In the current study, the tandem blade technology is applied to an STFF tandem cascade for the first time, and a 2D STFF tandem cascade is preliminarily designed. Through the modification design of the tandem airfoils and their configuration (axial overlap, AO and percent pitch, PP), the coefficients of total pressure loss and loading are reduced by 4% and 8.58%, respectively. Furtherly, the impact of tandem configurations on the performance is parametrically investigated by numerical simulations. The results indicate that compared with AO, the performance under design incidence is more sensitive to PP except for the cases with PP exceeding a threshold value (1.15). PP dominates the loss and load by controlling the evolution of the FB wake and the shock structure of FB and RB, while AO mainly adjusts the entire shock system structure through the change of virtual shape, resulting in the variation in load distribution between FB and RB. It is worth noting that the overall loading and the total loss remain unchanged with increasing AO except for the tandem configurations (PP=1.05, AO≤−0.01), which make the flow structure in the gap region undergo a fundamental change. With the optimal tandem configuration (PP=1.05, AO=−0.01) and the modified tandem blades (The ratios of chord length and camber for FB over RB is 0.67 and 0.5, respectively), the total pressure loss coefficient is further reduced by 19.7% in comparison with the preliminary tandem design.

Experimental investigation of shock–shock interactions with variable inflow Mach number

Experiments on shock–shock interactions were conducted in a transonic–supersonic wind tunnel with variable free-stream Mach number functionality. Transition between the regular interaction (RI) and the Mach interaction (MI) was induced by variation of the free-steam Mach number for a fixed interaction geometry, as opposed to most previous studies where the shock generator angles are varied at constant Mach number. In this paper, we present a systematic flow-based post-processing methodology of schlieren data that enables an accurate tracking of the evolving shock system including the precise and reproducible detection of RI$$\rightleftarrows $$ ⇄ MI transition. In line with previous experimental studies dealing with noisy free-stream environments, transition hysteresis was not observed. However, we show that establishing accurate values of the flow deflections besides the Mach number is crucial to achieve experimental agreement with the von Neumann criterion, since measured flow deflections deviated significantly, up to $$1.2^{\circ }$$ 1 . 2 ∘ , from nominal wedge angles. We also report a study conducted with a focusing schlieren system with variable focal plane that supported the image processing by providing insights into the three-dimensional side-wall effects integrated in the schlieren images.

New Supersonic Loss Model for the Preliminary Design of Transonic Turbine Blades and the Influence of Pitch

In order to produce a more efficient design of a compact turbine driving a cryogenic engine turbo-pump for a satellite delivering rocket, a new supersonic loss model is proposed. The new model was constructed based on high-quality published data, composed of Schlieren photographs and experimental measurements, that combined provided a unique insight into the mechanisms driving supersonic losses. Using this as a cornerstone, model equations were formulated that predict the critical Mach number and shock loss and shock-induced mixing loss as functions of geometrical (i.e., blade outlet and uncovered turning angle and trailing edge thickness) and operational parameters (i.e., exit Mach number). A series of highly resolved CFD numerical simulations were conducted on an in-house designed state-of-the-art transonic turbine rotor row (around unity aspect ratio (AR)) to better understand changes in the shock system for varying parameters. The main outcome showed that pitch to chord ratio has a powerful impact on the shock system, and thus on the manner by which shock loss and shock-induced mixing loss is distributed to compose the overall supersonic losses. The numerical loss estimates for two pitch to chord ratios—t⁄c = 0.70 and t⁄c = 0.98—were compared with absolute loss data of a previously published similar blade with satisfactory agreement. Calibrated equations are provided to allow hands-on integration into existing overall turbine loss models, where supersonic losses play a key role, for further enhancement of preliminary turbine design.

Focusing Schlieren Visualization of Transonic Turbine Tip-Leakage Flows

This paper presents a focusing schlieren system designed for the investigation of transonic turbine tip-leakage flows. In the first part, the functional principle and the design of the system are presented. Major design considerations and necessary trade-offs are discussed. The key optical properties, e.g., depth of focus, are verified by means of a simple bench test. In the second part, results of an idealized tip-clearance model as well as linear cascade tests at engine representative Reynolds and Mach numbers are presented and discussed. The focusing schlieren system, designed for minimum depth of focus, has been found to be well suited for the investigation of three-dimensional transonic flow fields in turbomachinery applications. The schlieren images show the origin and growth of the tip-leakage vortex on the blade suction side. A complex shock system was observed in the tip region, and the tip-leakage vortex was found to interact with the suction side part of the trailing edge shock system. The results indicate that transonic vortex shedding is suppressed in the tip region at an exit Mach number around M 2 , i s = 0.8.

Effect of intermediate aerodisk mounted sharp tip spike on the drag reduction over a hemispherical body at Mach 2.0

Reduction of forebody drag in high speed flying vehicles such as rockets and missiles are of high research interest in the present time. In the present research, drag reduction obtained by using an intermediate aerodisk mounted sharp tip spike has been investigated using computational studies at Mach number of 2.0. The flowfield over a hemispherical blunt body with an intermediate aerodisk mounted sharp tip spike is investigated at zero degree angle of attack and the amount of drag reduction obtained is then compared with that of a conventional sharp tip spike mounted hemisphere. The presence of an intermediate aerodisk changes the flow physics and shock system over the blunt body. The change in the system of shock waves by mounting an intermediate aerodisk results in a higher percentage (20% higher) of drag reduction generated by the blunt spiked body moving at a supersonic speed of Mach 2.0. Use of intermediate aerodisk proves to be beneficial in terms of drag reduction for spike lengths ranging beyond the critical length.

TEST BENCH FOR INVESTIGATION OF WAVE DEFORMATION STRENGTHENING PROCESSES

In the paper there are described designs of test benches to investigate the regularities of wave deformation strengthening processes. The advantages and disadvantages of well-known designs are revealed. A design of a new advanced test bench having wider technological potentialities and saved from the drawbacks revealed of the equipment created earlier is offered. A new design of the bench allows investigating the influence upon a process of a wave deformation strengthening of the elements of a shock system the parameters of which are varied in a wide range and applying also a series of marks upon a tested surface of a sample with the assurance of a specified accuracy of their mutual disposition. The test bench developed is essential for the fulfillment of experimental investigations of the interconnection between wave deformation parameters, a shape, dimensions of samples to be strengthened and a card of micro-hardness of a strengthened surface layer.

Visualizing the Process of Forming a Shock Pulse in the Deformation Zone

The article raises the problem of visualizing fleeting processes occurring as a result of wave strain hardening (WSH). The features of this method are unique capabilities for controlling the parameters of the shock pulse. This allows, in contrast to other dynamic methods of the surface plastic deformation, forming the desired microhardness distribution diagram in the surface layer at a depth of 6- 8 mm, while ensuring the required uniformity of hardening. The need to visualize this method is explained by the complexity of the analytical description of the ongoing wave processes in the shock system and the loading medium. Developing a visualization technique based on a model of the process of wave strain hardening consists of several stages. The stages include setting the initial and boundary conditions of the simulated elements, their physical-mechanical properties, loading conditions, the type of the mesh, the process conditions. The created model allows you to visually track the shock pulse movement after the striker hits the statically pressed waveguide against the loading medium, and at the same time to see the generation of the reflected deformation wave (the tail of the shock pulse) and its effect on the shock system elements and the loading medium. The results will make it possible to develop shock systems with the highest efficiency.

ПІДВИЩЕННЯ ДОВГОВІЧНОСТІ СФЕРИЧНИХ ШАРНІРІВ ЗМІЦНЕННЯМ КУЛЬОВИХ ПАЛЬЦІВ СТАТИКО-ІМПУЛЬСНОЮ ОБРОБКОЮ

The possibility of improving the durability of spherical sliding hinges due to the strengthening of the incomplete spherical surface of ball fingers by static-pulse processing is considered. The review of recent researches and publications was carried out and promising directions for increasing the durability of ball joints were established. The influence of the shock system parameters on the shape and amplitude of the impact pulse is analyzed. The recommended range of correlations of the geometric parameters of the elements of the shock system is established. On the basis of theoretical and experimental studies, a model of shock system with static load of the boom and tool, as well as a bipolar shock treatment scheme is proposed. The method of calculating the parameters of the shock system and the mathematical dependences have been developed. The model of the mechanical impulse generator of shock impact machine with static load of the boom and the tool according to the bipolar impact processing scheme is proposed. The method and algorithm of calculation of parameters of the generator of mechanical impulses of the device for strengthening of incomplete spherical surfaces is developed.