This paper presents the results of computational fluid dynamics (CFD)-aided design calculations of a transonic linear cascade wind tunnel. The purpose of the wind tunnel is to generate data for the validation of numerical methods employed to calculate aerodynamic damping for forced response cases in transonic compressors. It is common for transonic wind tunnels to use transonic walls (perforated walls with controlled suction) to adjust the transonic flow in the experiment. Unfortunately, perforated walls are difficult to model in CFD simulations, and they complicate the validation process. One of the goals of the new tunnel is not to use perforated walls. The main difficulty in the design of a transonic linear cascade is achieving periodic flow for the central blades due to shock reflections from the side walls and the sensitivity of transonic flow to small changes in geometry. Other design constraints are the maximum available mass flow of 4.5 kg/s and the minimum required blade thickness of 2 mm for instrumentation. The purpose of the current CFD simulations is to determine the optimum geometry (sidewalls, tailboards, and throttle) of the tunnel with the goal of achieving near periodic flow conditions for the central blade channels at the similar condition in a typical transonic compressor.
Accumulating evidence supports the active involvement of vascular inflammation in atherosclerosis pathogenesis. Vascular inflammatory events within atherosclerotic plaques are predominated by innate antigen-presenting cells (APCs), including dendritic cells, macrophages, and adaptive immune cells such as T lymphocytes. The interaction between APCs and T cells is essential for the initiation and progression of vascular inflammation during atherosclerosis formation. B7-CD28 family members that provide either costimulatory or coinhibitory signals to T cells are important mediators of the cross-talk between APCs and T cells. The balance of different functional members of the B7-CD28 family shapes T cell responses during inflammation. Recent studies from both mouse and preclinical models have shown that targeting costimulatory molecules on APCs and T cells may be effective in treating vascular inflammatory diseases, especially atherosclerosis. In this review, we summarize recent advances in understanding how APC and T cells are involved in the pathogenesis of atherosclerosis by focusing on B7-CD28 family members and provide insight into the immunotherapeutic potential of targeting B7-CD28 family members in atherosclerosis. Abbreviations: APC = antigen presenting cell, ApoE = apolipoprotein E, BTLA = B and T lymphocyte attenuator, CTLA-4 = cytotoxic T lymphocyte antigen-4, DC = dendritic cell, ICOS/ICOSL = inducible costimulator and ligand, IFN-γ = interferongamma, IL = interleukin, ITIM = immunoreceptor tyrosine-based inhibitory, LDL = low-density lipoprotein, Ldlr = low-density lipoprotein receptor, MD-2 = myeloid differentiation-2, PD-1/PD-L1 = programmed death-1/programmed death-1 ligand, TLR = toll-like receptor, Treg = regulator T cell, TREM = triggering receptors expressed on myeloid cells.
Plasma actuation is a novel method for axial compressor flow control with advantages of short response time and broad frequency range. Numerical simulation of tip leakage vortex control in a low speed axial compressor with pulsed plasma actuation is performed. Millisecond pulsed dielectric barrier discharge plasma actuation with different frequencies are generated on the inner wall of compressor casing at the rotor leading edge. Scale adaptive hybrid Reynolds-averaged Navier-Stokes/large eddy simulation method based on shear stress transport turbulence model is adopted. The plasma actuation is simplified as a body force in the simulation. Results show that the frequency has a strong influence on the control effect of pulsed plasma actuation. Pulsed plasma actuation with frequency of 0.25 blade passing frequency (BPF), 0.5 BPF and 1.0 BPF extend the compressor’s stability range effectively. The mechanism is tip leakage vortex oscillation in the stream wise direction through coupling between unsteady plasma actuation and tip leakage flow. However, pulsed plasma actuation with frequency of 0.125 BPF, 2 BPF and 3 BPF fails to improve the stability range. The mechanism of pulsed plasma actuation at 2 BPF and 3 BPF is similar to that with steady plasma actuation, which is only stream wise boundary layer acceleration. The oscillation of tip leakage vortex in the stream wise direction can’t occur. For the pulsed plasma actuation at 0.125 BPF, its frequency is too low to get enough control effect.
In modern transonic compressors, forced response can occur at high-order modes and at high-reduced frequencies. To understand this phenomenon, a new cascade test-rig is being built to provide configurations and validations for the forced response simulations of transonic compressors. With the aid of Computation Fluid Dynamics (CFD) optimizations, the test section shape was roughly determined before. The purpose of this paper is to provide the finalization process of the cascade test-rig design including a transonic nozzle and blade tip gaps. Hence, the steady and unsteady simulations are employed based on three different geometries: test section, test rig with nozzle, and test rig with 1% tip gap. The simulation results show that the unsteadiness in the test rig is related mainly to the oscillation performance of the shock waves in the passage. The comparison in the test rig with and without tip gap confirms that tip gap can reduce the unsteady pressure. The unsteady pressure reflection due to the tailboards, especially on the bottom tailboards, indicates this problem needs to be thoroughly considered in the installation and testing.
A linear aeroelastic rig was designed to serve as a validation facility for forced response research in axial compressors. This rig focuses on the study of aerodynamic damping at high-reduced frequencies when the central blade oscillates in a controlled manner. The steady and unsteady flow field of the rig has been numerically investigated previously. This paper aims to understand the pressure perturbation throughout the domain, which will give more insight into the actual transonic linear cascade rig and will improve the design of the test rig in some aspects. Such aspects are the tip gaps of the side blades that with the previously optimized upper inclined wall and tailboards are of importance in keeping flow periodicity. The design process has shown that these components do influence the unsteady pressure distribution, which might reduce the accuracy of the experiments. Thus, the aeroelastic cascade itself needs detailed investigations on the systematic accuracy losses in the unsteady testing due to the current design layout. This paper presents the impacts and mechanisms of tip gaps, upper inclined wall, and bottom tailboard on the test rig's aeroelastic performance. It provides a new validation reference for cascade test results with a perspective on the numerical studies, which can introduce a correction procedure on the existing test rig or on future cascade designs.
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