Rotating stall is an unsteady flow phenomenon that appears in both axial and centrifugal compressors. It is detrimental to the performance of the compressor, significantly narrowing its operating range. Numerical modeling of this phenomenon has been a major area of investigation for axial compressors with some success. While stall occurs less often in centrifugal compressors than axial ones, it can be much harder to predict. Some preventive measures are known but are mostly rules of thumb developed through experimental experience. This work focuses on the detection of impeller rotating stall using computational fluid dynamics. A compressor was chosen that has demonstrated rotating stall instabilities with different diffuser lengths and return vanes. Unsteady numerical simulations were performed on full 360 models of this geometry. The transient simulations were conducted using distributed processing on high-performance servers. The objective was to determine the accuracy in which rotating stall can be captured in simulations. For this purpose, simulation results were compared to experimental results for the same compressor and show a good correlation between the experimental and numerical tests.

Flow-trimming base designs for lower flow applications are widely used in the turbo-machinery industry to minimize development costs. This process requires the use of the same casing as the base design, along with a decrease in the flow path width of the impeller, diffuser, crossover, and return vane. Two stages: a baseline and a flow-trimmed impeller, diffuser and return vane are studied in this paper to review impacts on performance and their underlying causes. To measure the performance changes of the two rigs, a traverse survey for flow angle and total pressure was done at the locations of diffuser inlet, return vane leading edge and stage discharge. It was found that the performance difference between the base impeller and trimmed one is very little. However, diffuser performance of the base rig is better than the flow-trimmed rig. Diffuser data shows frictional losses increased in the flow-trimmed rig. Rig data also suggests that increased friction in the trimmed stage changes the flow angle at the return vane leading edge compared to the base stage. This increases the loss further for the flow-trimmed rig because of resulting negative incidence on the return vane relative to the base rig. Data suggests that while flow-trimming may be a valid design approach for impellers, additional issues arise when downstream stationary components are trimmed.

Bardet-Biedl syndrome (BBS) is a rare ciliopathy for which there are no current effective treatments. BBS is a genetically heterogeneous disease, though the M390R mutation in BBS1 is involved in approximately 25% of all genetic diagnoses of BBS. The principle features of BBS include retinal degeneration, obesity, male infertility, polydactyly, intellectual disability, and renal abnormalities. Patients with mutations in BBS genes often present with night blindness within the first decade of life, which progresses to complete blindness. This is due to progressive loss of photoreceptor cells. Male infertility is caused by a lack of spermatozoa flagella, rendering them immobile. In this study, we have crossed the wild-type human BBS1 gene, driven by the CAG promoter, onto the Bbs1 M390R/M390R mouse model to determine if ectopic expression of BBS1 rescues male infertility and retinal degeneration. qRT-PCR indicates that the BBS1 transgene is expressed in multiple tissues throughout the mouse, with the highest expression seen in the testes, and much lower expression in the eye and hypothalamus. Immunohistochemistry of the transgene in the eye showed little if any expression in the photoreceptor outer nuclear layer. When male Bbs1 M30R/M390R ;BBS1 TG+ mice are housed with WT females, they are able to sire offspring, indicating that the male infertility phenotype of BBS is rescued by the transgene. Using electroretinography (ERGs) to measure retinal function and optical coherence tomography to measure retinal thickness, we show that the transgene does not confer protection against retinal degeneration in Bbs1 M300R/M390R ;BBS1 TG+ mice. The results of this study indicate the male infertility aspect of BBS is an attractive target for gene therapy.

An experimental study on the use of synthetic jet actuators for lift control on a generic compressor airfoil is conducted. A wind tunnel model of a NACA 65(2)-415 airfoil, representative of the cross section of an Inlet Guide Vane (IGV) in an industrial gas compressor, is 3D-printed. Nine synthetic jet actuators are integrated within a planar wing section with their slots covering 61% of pressure side of the airfoil span, located 13% chord upstream of the trailing edge. The Helmholtz frequency of the slot is matched closely with the piezoelectric element material frequency. The slot is designed so that the bi-morph actuation creates a jet normal to the airfoil surface. By redirecting or vectoring the shear layer at the trailing edge, the synthetic jet actuator increases lift and decreases drag on the airfoil without a mechanical device or flap. Tests are performed at multiple Reynolds number ranging from Re=150,000 to Re=450,000. The increased lift of the integrated synthetic jet actuator is dependent on the Reynolds number and free stream velocity, the actuation frequency, and angle of attack. For actuation at 1450 Hz the synthetic jet actuator increases lift up to 7%. The synthetic jet increases L/D up to 15%. Velocity contours obtained through PIV show that the synthetic jet turns the trailing edge shear layer similar to a Gurney flap.

Labyrinth seals are widely used in industrial multistage centrifugal compressors to reduce internal leakage and maintain compressor performance for a prolonged operation time. The leakage flow across the shroud seal of covered impellers and the hub seal of the rotating shaft has an important effect on the compressor performance. The amount of leakage flow is primarily a function of seal running clearances, which is typically designed based on the compressor working environment, such as pressure and temperature conditions. The present paper discusses the experimental and numerical studies of seal clearance impact on the performance and operation of a single stage centrifugal compressor. Two experimental campaigns of running a medium-flow coefficient impeller and a low-flow coefficient impeller with various radial clearances of the impeller shroud and the hub labyrinth seal were conducted based on the configuration of the impeller and the return channel system in a closed-loop compressor test rig. The experimental investigation consists of both the overall stage performance test and the traverse test of the flow field downstream of the impeller using three-hole Cobra probes. Static pressure taps were arranged in the impeller shroud cavity in order to obtain the stream-wise pressure distribution. CFD simulations were then performed to compare with the test results. The paper presents the analysis of test data and simulation results of five arrangements of the impeller shroud and the hub seal radial clearances. The impacts of seal clearance height on stage efficiency and head are quantitatively evaluated. The impact on impeller internal flow field and cavity pressure distributions and swirl angle are discussed. Findings from this study are that efficiency reduction with increased seal clearance was as expected, but impeller Euler work was significantly reduced. CFD simulation was validated as a tool for predicting these effects and provides some understanding of the flow mechanisms.