Casing Boundary Layer Research Articles

Flow Control in an Aggressive Interturbine Transition Duct Using Low Profile Vortex Generators

This paper presents an experimental investigation of the flow mechanisms in an aggressive interturbine transition duct with and without low-profile vortex generators flow control. The interturbine duct had an area ratio of 1.53 and a mean rise angle of 35 deg. Measurements were made inside the annulus at a Reynolds number of 150,000. At the duct inlet, the background turbulence intensity was raised to 2.3% and a uniform swirl angle of 20 deg was established with a 48-airfoil vane ring. Results for the baseline case (no vortex generators) showed the flow structures within the duct were dominated by counter-rotating vortices and boundary layer separation in both the casing and hub regions. The combination of the adverse pressure gradient at the casing's first bend and upstream low momentum wakes caused the boundary layer to separate on the casing. The separated flow on the casing appears to reattach at the second bend. Counter-rotating and corotating vortex generators were installed on the casing. While both vortex generators significantly decreased the casing boundary layer separation with consequential reduction of overall pressure losses, the corotating configuration was found to be more effective.

The use of satellite‐measured aerosol optical depth to constrain biomass burning emissions source strength in the global model GOCART

Simulations of biomass burning (BB) emissions in chemistry transport models strongly depend on the inventories that define emission source location and strength. We use 13 global biomass burning emission estimates, including the widely used Global Fire Emission Database (GFED) monthly and daily versions, Fire Radiative Power (FRP)‐based Quick Fire Emission Data set QFED, and 11 calculated emissions from different combinations of burned area based on the Moderate Resolution Imaging Spectroradiometer (MODIS) products, effective fuel load, and species emission factors as alternative inputs to the global Goddard Chemistry Aerosol Radiation and Transport (GOCART) model. The resultant simulated aerosol optical depth (AOD) and its spatial distribution are compared to AOD snapshots measured by the MODIS instrument for 124 fire events occurring between 2006 and 2007. This comparison exposes the regional biases of each emission option. GOCART average fire AOD values compare best to MODIS‐measured AOD when the daily GFED inventory is used as input to GOCART. Even though GFED‐based emission options provide the lowest emissions in the tropics, GFED‐based GOCART AOD compares best with MODIS AOD in tropical cases. Fire‐counts‐based emission options give the largest emission estimates in the boreal regions, and the model performs best at higher latitudes with these inputs when compared to MODIS. Comparison of total annual BB emissions by all inventories suggests that burned area estimates are usually the largest source of disagreement. It is also shown that the quantitative relationship between BB aerosol emission rate and model‐simulated AOD is related to the horizontal plume dispersion, which can be approximated by the wind speed in the planetary boundary layer in most cases. Thus, given average wind speed of the smoke plume environment, MODIS‐measured AOD can provide a constraint to the strength of BB sources at the level of individual plumes.

A comparative estimate of acoustic emission of thin-walled structures excited by a turbulent boundary layer for various representations of the mutual spectrum

We present the results of comparative studies of the acoustic emission of thin-walled structures excited by the field of near-wall pressure pulsations of a turbulent boundary layer for cases when the mutual spectrum of the field is described by a multiplicative model or a model with elliptical windows. A universal dependence is obtained for determining the difference in the acoustic emission levels of elastically inertial systems using to considered models of representing the mutual spectrum

A numerical investigation of the turbulent Stokes–Ekman bottom boundary layer

AbstractIn the present paper turbulent mixing in the Stokes–Ekman bottom boundary layer is investigated analytically and by wall-resolving large-eddy simulations (LES). The analytical solution shows that when the Rossby number $\mathit{Ro}\ensuremath{\sim} 1$ oscillation and rotation interact with each other, this gives rise to a thickening of the boundary layer compared with the purely oscillating or the purely rotating case. The solution also shows the presence of elliptical patterns developing on the horizontal planes that shrink when approaching the low latitudes. In the turbulent regime, a LES was applied for an east–west tidal current, considered at three different latitudes in the Northern Hemisphere, namely, the polar case, the mid-latitude case ($4{5}^{\ensuremath{\circ} } $) and the quasi-equatorial case (${5}^{\ensuremath{\circ} } $). The Reynolds number of the simulation, based on the viscous penetration depth and the frequency of the purely oscillatory flow, was set equal to ${\mathit{Re}}_{\delta } = 1790$. The analysis suggests that rotation has two main effects on the flow field: in the polar case, rotation tends to delay the cyclic re-transition to turbulence and to narrow the turbulent phases of the cycle. Also, rotation suppresses vertical fluctuations of velocity and redistributes energy from the streamwise direction to the spanwise direction. It is noteworthy that the high-latitude effect makes the turbulent field substantially different from the reference Stokes boundary layer case, whereas the low-latitude effects appear to be of secondary importance, owing to the weakness of the rotation rate. Consequently, the study shows that the Stokes boundary layer may be representative of the oceanic bottom boundary layer in the low-latitude cases ($\mathit{Ro}\gt 1$ cases in our simulations). Conversely, it cannot be considered as archetypal of the oceanic boundary layer at high latitudes ($\mathit{Ro}\lt 1$ case of our study), where the vertical background vorticity profoundly modifies the turbulent field.

The Internal Structure of the Tip Leakage Vortex Within the Rotor of an Axial Waterjet Pump

The complex flow field in the tip region of a turbomachine rotor, including the tip leakage flow and tip leakage vortex (TLV), has been studied for decades. Yet many associated phenomena are still not understood. This paper provides detailed data on the instantaneous and phase-averaged inner structures of the tip flow and evolution of the TLV. Observations are based on series of high resolution planar particle image velocimetry measurements performed in a transparent waterjet pump fitted into an optical refractive index-matched test facility. Velocity distributions and turbulence statistics are obtained in several meridional planes inside the rotor. We observe that the instantaneous TLV structure is composed of unsteady vortex filaments that propagate into the tip region of the blade passage. These filaments are first embedded into a vortex sheet, which is generated at the suction side of the blade tip, and then they wrap around each other and roll up into the TLV. We also find that the leakage vortex induces flow separation at the casing endwall and entrains the casing boundary layer with its counter-rotating vorticity. As it propagates in the rotor passage, the TLV migrates toward the pressure side of the neighboring blade. Unsteadiness associated with vortical structures is also investigated. We notice that, at early stages of the TLV evolution, turbulence is elevated in the vortex sheet, in the flow entrained from the endwall, and near the vortex core. Interestingly, the turbulence observed around the core is not consistent with the local distribution of turbulent kinetic energy production rate. This mismatch indicates that, given a TLV section, production likely occurs at preceding stages of the vortex evolution. Then, the turbulence is convected to the core of the TLV, and we suggest that this transport has substantial component along the vortex. We observe that the meandering of vortex filaments dominates the flow in the passage and we decompose the unsteadiness surrounding the TLV core to contributions from interlaced vortices and broadband turbulence. The two contributions are of the same order of magnitude. During late stages of its evolution, TLV breakdown occurs, causing rapid broadening of the phase-averaged core, with little change in overall circulation. Associated turbulence occupies almost half the width of the tip region of blade passage and turbulence production there is also broadly distributed. Proximity of the TLV to the pressure side of the neighboring blade also affects entrainment of flow into the incoming tip region.

A Suggested Mechanism of Significant Stall Suppression Effects by Air Separator Devices in Axial Flow Fans

Abstract Radial-vaned air separators show a strong stall suppression effect in an axial flow fans. From a survey of existing literature on the effects and the author's data, a possible mechanism for the significant effects has been proposed here. The stall suppression is suggested to have been achieved by a combination of the following several effects; (1) suction of blade and casing boundary layers and elimination of embryos of stall, (2) separation and straightening of reversed swirling flow from the main flow, (3) induction of the fan main flow toward the casing wall and enhancement of the outward inclination of meridional streamlines across the rotor blade row, thus keeping the Euler head increase in the decrease in fan flow rate, and (4) reinforcement of axi-symmetric structure of the main flow. These phenomena have been induced and enhanced by a stable vortex-ring encasing the blade tips and the air separator. These integrated effects appear to have caused the great stall suppression effect that would have been impossible by other types of stall prevention devices. Thus the author would like to name the device “tip-vortex-ring assisted stall suppression device”.

An Experimental Study of Tip Vortex Cavitation Inception in an Axial Flow Pump

The interaction of the blade tip with the casing boundary layer and the leakage flow may lead to a kind of cavitation namely tip vortex cavitation. In this study, the onset of tip vortex cavitation was experimentally investigated in an axial flow pump. For a constant speed and a fixed angle of attack and by changing the flow rate, the pump head, input power, output power and efficiency were calculated and the pump characteristic curves were obtained. The cavitation phenomenon was observed with a camera and a stroboscope. Finally, the critical flow region, which tip vortex cavitation might have occurred, was identified. The results show that just by adjusting the flow rate, out of the specified region, the possibility of occurring tip vortex cavitation, decreases to a great extent.

STUDI EKSPERIMENTAL ALIRAN SEKUNDER UNTUK AXIAL COMPRESSOR CASCADE STAGGER KUAT DENGAN DAN TANPA TIP-CLEARANCE: DISTRIBUSI TEKANAN STATIS PADA PERMUKAAN BLADE

Secondary Flow Experimental Study for Axial Compressor Cascade Strong Stagger With and Without Tip-Clearance: Static Pressure Distribution on Blade Surface. The performance of blade cascade is influenced by thegrowth and boundary layer's separation along blade surface and endwall (casing and hub). The secondary flow whichhappens near hub and casing compressors is three dimentional flow separation phenomenon comes from interactionblade boundary layer with casing and hub boundary layers in the compressor. The secondary flow causes secondarylosses, blockage effect, and turning angle (deflection) distribution along blade span. The result of the research showsthat the increase of the angle of attack reveals lines of constan pressure to be curved forward (upstream) or pressuregives rise to spanwise caused by a strong curl flow. Separation is also increase and cross between two blades. Hence,three dimentional separation region in corner also increase.

軸流ファンの失速防止におけるエアセパレータの効果のメカニズム(流体工学,流体機械)

Radial-vaned air separators show a strong stall improvement effect in axial flow fans. Changes in the fan internal flow patterns achieved by the device have been made clear by Pitot-traversing mesurements. With a decrease in the fan flow rate the meridional streamline inclinations through the rotor blades have become more and more abrupt together with the circumferential velocities enlarged in the region, in contrast to relatively insensitive behavior tendency of the streamlines and flow patterns in the solid-wall condition. The stall suppression are suggested to have been achieved by the followings air separator effects; (1) suction of inflow casing boundary layers and elimination of embryos of stall, (2) separation of reversed flow from the main flow, (3) induction of the flow toward the casing wall and strengthening of stream-surface inclination, and (4) reinforcement of axi-symmetric flow structure. Combination of them appears to have caused the great stall suppression effect that would have been impossible by other types of stall prevention devices.

Cylindrical three-hole pressure probe calibration for large angular range

This paper presents a brand new method to calibrate a Cylindrical Three-Hole Probe (CTHP) in a “non-nulling” operating mode. This calibration method employs the definition of a new normalization factor used in the calibration coefficients of the probe. By means of this new normalization, singular points are prevented from appearing in the calibration coefficients. In addition, the angular range attainable when using this new calibration is ±70 ∘, while the typical angular range of traditional calibration is approximately ±30 ∘. To validate this study, an uncertainty analysis of the probe using this new method is carried out, resulting in significantly low uncertainties for the whole angular range of the probe. Complementarily, the influence of the angular distance between the holes of the probe on both angular range and maximum uncertainties is also performed in the paper. From this analysis, it is established that the optimal angular separation for the holes should be chosen to be between 50 and 60 degrees. Finally, to illustrate the usefulness of this procedure, a set of experimental measurements were conducted downstream of the rotor of an axial turbomachine, using the new normalization factor in a CTHP with an angular distance of 60 degrees between the holes. The results revealed that the complex, unsteady flow within the blade passages can be perfectly captured, including those regions with high variations in the flow angle, like the shear layers of the wake fluid or both casing and hub boundary layers. In summary, this newly developed calibration method enables the measurement of large variations of the flow angle, in particular, up to 140 degrees, increasing in 80 degrees the typical angular range of the traditional calibration.

Wall pressure fluctuation spectra due to boundary-layer transition

Boundary-layer transition has been expected to be an important contributor to sensor flow-induced self-noise. The pressure fluctuations caused by this spatially bounded, and intermittent, phenomenon encompass a very wide range of wavenumbers and temporal frequencies. Here, we analyze the wavevector–frequency spectrum of the wall pressure fluctuations due to subsonic boundary-layer transition as it occurs on a flat plate under zero-pressure gradient conditions. Based on previous measurements of the statistics of the boundary-layer intermittency, it is found that transition induces higher low-streamwise wavenumber wall pressure levels than does a fully developed turbulent boundary layer that might superficially exist at the same location and at the same Reynolds number. The transition zone spanwise wavenumber pressure components are virtually unchanged from the fully developed turbulent boundary-layer case. The results suggest that transition may be more effective than the fully developed turbulent boundary layer in forcing structural excitation at low Mach numbers, and it may have a more intense radiated noise contribution. This may help explain increases in measured sensor self-noise when the sensors are placed near the transition zone. We believe, based on the presented analytical calculation and numerical simulation, that the rapid growth and subsequent decay of turbulent spots in the intermittent transition zone causes the higher low-(streamwise) wavenumber spectra.

Spectral Stability of Noncharacteristic Isentropic Navier–Stokes Boundary Layers

Building on the work of Barker, Humpherys, Lafitte, Rudd, and Zumbrun in the shock wave case, we study stability of compressive, or shock-like, boundary layers of the isentropic compressible Navier–Stokes equations with γ-law pressure by a combination of asymptotic ODE estimates and numerical Evans function computations. Our analytical results include convergence of the Evans function in the shock and large-amplitude limits and stability in the large-amplitude limit, the first rigorous stability result for other than the nearly constant case, for all \({\gamma\geqq 1}\). Together with these analytical results, our numerical investigations indicate stability for γ ϵ [1, 3] for all compressive boundary-layers, independent of amplitude, save for inflow layers in the characteristic limit (not treated). Expansive inflow boundary-layers have been shown to be stable for all amplitudes by Matsumura and Nishihara using energy estimates. Besides the parameter of amplitude appearing in the shock case, the boundary-layer case features an additional parameter measuring displacement of the background profile, which greatly complicates the resulting case structure. Inflow boundary layers turn out to have quite delicate stability in both large-displacement (shock) and large-amplitude limits, necessitating the additional use of a mod-two stability index studied earlier by Serre and Zumbrun in order to decide stability.

Three-Dimensional Wake Forcing Functions Generated by a High-Speed Rotor

A series of experiments are described that are directed at investigating and quantifying the inherent three-dimensionality and fundamental unsteady-flow characteristics of unsteady aerodynamic forcing functions generated by high-speed compressor rotors for application to forced response. With a midspan rotor-relative inlet Mach number of 0.6, three-component velocity and unsteady-static-pressure data defining the spanwise nature of the rotor wake are acquired and analyzed at two axial locations, in both the inlet guide vane freestream and wake regions. The slanted hot-film technique enables evaluation of the ensemble-averaged-velocity field and the rms of this ensemble-averaged velocity. Data show that the rotor-wake unsteadiness is highest in the blade wake, the vortex regions, and the casing boundary layer. A strip theory approach is used to analyze these three-dimensional data. The rotor-wake data are also correlated with empirical correlations. After Fourier decomposition of the axial and tangential velocity components, a two-dimensional vortical-potential gust splitting analysis is implemented, and the vortical and potential harmonic wake gust forcing functions are determined.

Effect of Blade Loading on the Structure of Tip Leakage Flow in a Forward-Swept Axial-Flow Fan

An experimental analysis using three-dimensional laser Doppler velocimetry (LDV) measurement and computational analysis using the Reynolds stress model of the commercial flow solver, FLUENT, have been conducted to give a clear understanding of the effect of blade loading on the structure of tip leakage flow in a forward-swept axial-flow fan operating at the maximum efficiency condition (⊘ = 0.25) and two off-design conditions (⊘ = 0.21 and 0.30). As the blade loading increased, the onset position of the rolling-up of tip leakage flow moved upstream and the trajectory of tip leakage vortex (TLV) center was more inclined toward the circumferential direction. Because the casing boundary layer became thicker and the mixing between the through-flow and the leakage jet with the different flow direction was enforced, the streamwise vorticity decayed more rapidly with the blade loading increasing. A distinct TLV was observed downstream of the blade trailing edge at ⊘ = 0.30, but it was not found at ⊘ = 0.21 and 0.25. In comparison with LDV measurement data, the computed results predicted the complex viscous flow patterns inside the tip region in a reliable level. Influence of the relative motion of the casing wall on the structure of tip leakage flow was also investigated. Since it enhanced the strength of TLV by dragging the fluid through the tip clearance region, the magnitudes of the streamwise vorticity for the stationary casing wall were considerably larger than those for the rotating casing wall. Therefore, for the rotating casing wall, the high momentum region related with the blockage effect of TLV was reduced in comparison with that of the stationary casing wall.

An investigation of the heat transfer and static pressure on the over-tip casing wall of an axial turbine operating at engine representative flow conditions. (I). Time-mean results

The over-tip casing of the high-pressure turbine in a modern gas turbine engine is subjected to strong convective heat transfer that can lead to thermally induced failure (burnout) of this component. However, the complicated flow physics in this region is dominated by the close proximity of the moving turbine blades, which gives rise to significant temporal variations at the blade-passing frequency. The understanding of the physical processes that control the casing metal temperature is still limited and this fact has significant implications for the turbine design strategy. A series of experiments has been performed that seeks to address some of these important issues. This article reports the measurements of time-mean heat transfer and time-mean static pressure that have been made on the over-tip casing of a transonic axial-flow turbine operating at flow conditions that are representative of those found in modern gas turbine engines. Time-resolved measurements of these flow variables (that reveal the details of the blade-tip/casing interaction physics) are presented in a companion paper. The nozzle guide vane exit flow conditions in these experiments were a Mach number of 0.93 and a Reynolds number of 2.7 × 10 6 based on nozzle guide vane mid-height axial chord. The axial and circumferential distributions of heat transfer rate, adiabatic wall temperature, Nusselt number and static pressure are presented. The data reveal large axial variations in the wall heat flux and adiabatic wall temperature that are shown to be primarily associated with the reduction in flow stagnation temperature through the blade row. The heat flux falls by a factor of 6 (from 120 to 20 kW/m 2). In contrast, the Nusselt number falls by just 36% between the rotor inlet plane and 80% rotor axial chord; additionally, this drop is near to linear from 20% to 80% rotor axial chord. The circumferential variations in heat transfer rate are small, implying that the nozzle guide vanes do not produce a strong variation in casing boundary layer properties in the region measured. The casing static pressure measurements follow trends that can be expected from the blade loading distribution, with maximum values immediately upstream of the rotor inlet plane, and then a decreasing trend with axial position as the flow is turned and accelerated in the relative frame of reference. The time-mean static pressure measurements on the casing wall also reveal distinct circumferential variations that are small in comparison to the large pressure gradient in the axial direction.

Synoptic‐scale transport of reactive nitrogen over the western Pacific in spring

Pathways of synoptic‐scale uplifted transport of pollutants from East Asia and their effects on chemical distributions of NOy species are investigated based on a subset of the aircraft data obtained during the NASA Transport and Chemical Evolution over the Pacific (TRACE‐P) experiment, conducted in February–April 2001. Meteorological and chemical analyses indicate that 73% of the uplifted transport was associated with warm conveyor belts (WCBs) and convective outflow (COF), which transported air masses strongly impacted by biomass burning over Southeast Asia. The rest (27%) of the uplifted air masses originated over coastal regions of northeast China, where fossil fuel combustion was a dominant source of pollutants. Both WCB associated with a midlatitude cyclone and COF associated with a stationary front over southeast China are examined in detail for the April 4 case. During the TRACE‐P period, low NOx(= NO + NO2)/NOy ratios in the WCB and COF indicate that a significant part of the NOx was oxidized to nitric acid (HNO3) and peroxyacetyl nitrate (PAN) during transport. Low HNO3/NOy ratios in the WCB and COF airstreams indicate that a large amount of HNO3 was removed during transport on timescales within 1–3 days. PAN was found to be the dominant form of NOy in air masses transported by the WCB and COF, likely due to the production of PAN in regions of biomass burning and industrial emissions, as well as due to the rapid removal of HNO3 during transport. For emissions that were transported to the free troposphere by WCBs and COF, about 10–20% of the NOy remained after transport to the free troposphere, and 30% of the NOy surviving in the boundary layer in limited cases. The results indicate that the WCB and COF provide both an efficient sink for HNO3 and an efficient mechanism for the transport of PAN from the boundary layer to the free troposphere over the western Pacific.

전향 축류형 홴에서의 익단 누설 유동 구조

The experiment using three-dimensional laser Dopperr velocimetery (LDV) measurements and the computation using the Reynolds stress model of the commercial code, FLUENT, were conducted to give a clear understanding on the structure of tip leakage flow in a forward-swept axial-flow fan operating at the maximum efficiency condition. The tip leakage vortex was generated near the position of the minimum wall static pressure, which was located at approximately 12% chord downstream from the leading edge of blade suction side, and developed along the centerline of the pressure trough within the blade passages. A reverse flow between the blade tip region and the casing, induced by tip leakage vortex, acted as a blockage on the through-flow. As a result, high momentum flux was observed below the tip leakage vortex. As the tip leakage vortex proceeded to the aft part of the blade passage, the strength of tip leakage vortex decreased due to the strong interaction with the through-flow and casing boundary layer, and the diffusion of tip leakage vortex caused by high turbulence. In comparison with LDV measurement data, the computed results predicted the complex viscous flow patterns inside the tip region, including the locus of tip leakage vortex center, in a reliable level.

Structure of Tip Leakage Flow in a Forward-Swept Axial-Flow Fan

An experimental analysis using three-dimensional laser Dopplervelocimetery (LDV) measurements and computational analysis usingthe Reynolds stress model of the commercial code, FLUENT, wereconducted to give a clear understanding on the structure of thetip leakage flow in a forward-swept axial-flow fan operating atthe peak efficiency condition, and to emphasize the necessity ofusing an anisotropic turbulence model for the accurate predictionof the tip leakage vortex. The rolling-up of the tip leakage flowwas initiated near the position of the maximum static pressuredifference, which was located at approximately 12% axial tipchord downstream from the leading edge of the blade, and developedalong the centerline of the pressure trough on the casing. Areverse flow between the blade tip and the casing due to the tipleakage vortex acted as a blockage on the through-flow. As aresult, high momentum flux was observed below the tip leakagevortex. As the tip leakage vortex proceeded to the aft part of theblade passage, the strength of the tip leakage vortex decreaseddue to the strong interaction with the through-flow and the casingboundary layer, and the diffusion of the tip leakage vortex byhigh turbulence. Through the comparative study of turbulencemodels, it was clearly shown that an anisotropic turbulence model,e.g., Reynolds stress model, should be used to predict reasonablyan anisotropic nature of the turbulent flow fields inside the tipleakage vortex. In comparison with LDV measurement data, thecomputed results predicted the complex viscous flow patternsinside the tip region in a reliable level.

Viscous Three-Dimensional Simulation of Transonic Compressor Stage on Parallel Hardware

The continued thrust toward more efe cient, economic, and lower-emission turbomachinery along with the reduced lead time available for design iterations and the high cost associated with extensive rig and engine tests keepspushing forwardthestateoftheart incomputationale uid dynamics. Thepaperstartsoffwitha discussion of the aeroengine development processand its timescales. The place and importanceof Navier -Stokesmethods in the development process are addressed, and the three-dimensional viscous codeemployed for aerodynamic design and analysisofturbomachinery atMotoren-und Turbinen-UnionMisintroduced. Abrieftreatmentofthecode is followed by a discussion of its implementation on parallel hardware architectures to reduce turnaround times for incorporation as an integral part of the design process; excellent performance on symmetric multiprocessing- parallelarchitecturesisdemonstrated.Thee rstthree-dimensionalviscoussimulationsandthee rstdetailedanalysis of thesingle-stagetransonic compressorrig attheTechnical University of Darmstadt, a research rig representative of modern high pressure compressor front stages, are presented. Computed results are compared to experimental data in terms of radial distributions derived from traverse data, in terms of rotor Mach number e elds derived from L2F data on S1 and S2 planes, and in terms of performance parameters critical to designers. The excellent agreementbetweensimulationsandexperimentsdemonstratesthecode' spredictivecapabilityforturbomachinery design. With qualitative and quantitativeagreement demonstrated, e owdetailsover the outer 40% span and in the tip region of the rotor are examined, based solely on computational results. Three-dimensional simulations with and without tip clearance are compared to two-and-one-half-dimensional simulations to separate the ine uence of tip leakage on the rotor blade Mach number e elds from other three-dimensional effects. The complex e ow near the tip, involving an interaction of casing boundary layer, blade boundary layer, shock systems, and tip, leakage e ow, is analyzed to further the understanding of highly loaded transonic compressors and to identify potential for performance improvements. The analysis explains the e ow features found in this research rig and identie es the mechanisms contributing to the rather high loss and blockage near the casing.

Calculation of Tip Clearance Effects in a Transonic Compressor Rotor

The flow through the tip clearance region of a transonic compressor rotor (NASA rotor 37) was computed and compared to aerodynamic probe and laser anemometer data. Tip clearance effects were modeled both by gridding the clearance gap and by using a simple periodicity model across the ungridded gap. The simple model was run with both the full gap height, and with half the gap height to simulate a vena-contracta effect. Comparisons between computed and measured performance maps and downstream profiles were used to validate the models and to assess the effects of gap height on the simple clearance model. Recommendations were made concerning the use of the simple clearance model. Detailed comparisons were made between the gridded clearance gap solution and the laser anemometer data near the tip at two operating points. The computed results agreed fairly well with the data but overpredicted the extent of the casing separation and underpredicted the wake decay rate. The computations were then used to describe the interaction of the tip vortex, the passage shock, and the casing boundary layer.