Thong Q. Dang

Experimental and computational study of perforated floor tile in data centers

Current CFD simulation studies of large data centers cannot model the detailed geometries of the perforated tiles due to grid size limitation. These studies often assume that the tile flow can be modeled as constant velocity based on a fully open tile. In this case, mass flux is enforced at the expense of under-predicting momentum flux; the error in momentum flux can be as high as a factor of four for a 25% open perforated tile. Since jet entrainment is a strong function of its initial momentum flux, this error can be significant with respect to predicting the mixing of the surrounding room air into the tile flow. Combined experimental and computational studies were carried out to quantify the importance of the detailed tile geometry, and it was found that proper prediction of the mixing process must account for the tile opening patterns. Suggestions of how to model the floor perforated tiles in data center CFD simulations are then presented.

Euler-Based Inverse Method for Turbomachine Blades, Part 2: Three-Dimensional Flows

The aerodynamic design method for turbomachine blades reported in part 1 is extended to three dimensions. In this inverse method, the blade pressure loading (i.e., pressure difference between blade upper and lower surfaces) and the blade thickness distributions are prescribed, and the corresponding blade camber surface is sought. The inverse problem is formulated using a pressure-loading boundary condition across the blade surfaces, and modification of the blade geometry is achieved using the flow-tangency conditions along the blade surfaces. The method is demonstrated for the design of axial-flow machines ranging from the subsonic to the supersonic flow regimes

High-Lift Propulsive Airfoil with Integrated Crossflow Fan

A concept for embedding a crossflow fan into a thick wing for lift enhancement and thrust production is proposed. The design places a crossflow fan propulsion system with raised inlet near the trailing edge of the wing. Flow is drawn in from the suction surface, energized, and expelled out the trailing edge. The integration of a crossflow fan within a modified Gottingen 570 airfoil section with 34% thickness to chord ratio is developed and simulated using the commercial CFD software Fluent. Unsteady sliding mesh calculations are used to visualize the flowfield and calculate fan performance and airfoil lift coefficient. The results of the CFD work show that the jet leaving the fan fills up the wake behind the airfoil, whereas the suction effect produced by the fan virtually eliminates flow separation at high angle of attack, yielding very high-lift coefficients. A system level analysis demonstrates the benefits of using an embedded crossflow fan for distributed aircraft propulsion. The system analysis yields tradeoffs between various design parameters and provides a basis for preliminary crossflow fan airfoil design.

Design of Simulated Server Racks for Data Center Research

Conducting experiments on real high-density computer servers can be an expensive and risky task due to the risks associated with unintended inlet temperatures that exceed the server’s red-line temperature limit. Presented herein is the development of the simulated chassis that mimic real computer servers. Briefly, twelve high-power simulated chassis were designed and built to accurately simulate the actual operating conditions of a real computer chassis in a data center. Each simulated chassis is designed to have approximately 300 Pa pressure drop at a flow rate of 600 cfm to represent a real IBM server chassis. Additionally, the simulated chassis are designed to match the thermal mass of a real server. Eight of the simulated chassis were designed to have constant speed fans and variable heating power while the remaining four chassis were designed to have variable speed fans and variable heating power. Further discussions about the design phase of the simulated chassis are the substantial part of this paper. Underlining the challenges and safety issues with high-power chassis, guidelines for designing and constructing a chassis that simulates the real environment of a typical data center are presented.Copyright

Improving Aerodynamic Matching of Axial Compressor Blading Using a Three-Dimensional Multistage Inverse Design Method

Current turbomachinery design systems increasingly rely on multistage CFD as a means to diagnose designs and assess performance potential. However, design weaknesses attributed to improper stage matching are addressed using often ineffective strategies involving a costly iterative loop between blading modification, revision of design intent, and further evaluation of aerodynamic performance. A scheme is proposed herein which greatly simplifies the design point blade row matching process. It is based on a three-dimensional viscous inverse method that has been extended to allow blading analysis and design in a multi-blade row environment. For computational expediency, blade row coupling is achieved through an averaging-plane approximation. To limit computational time, the inverse method was parallelized. The proposed method allows improvement of design point blade row matching by direct regulation of the circulation capacity of the blading within a multistage environment. During the design calculation, blade shapes are adjusted to account for inflow and outflow conditions while producing a prescribed pressure loading. Thus, it is computationally ensured that the intended pressure-loading distribution is consistent with the derived blading geometry operating in a multiblade row environment that accounts for certain blade row interactions. The viability of the method is demonstrated in design exercises involving the rotors of a 2.5 stage, highly loaded compressor. Individually redesigned rotors display mismatching when run in the 2.5 stage, evident as a deviation from design intent. However, simultaneous redesign of the rotors in their multistage environment produces the design intent, indicating that aerodynamic matching has been achieved.

Euler Correction Method for Two- and Three-Dimensional Transonic Flows

An Euler correction method, based on the Clebsch formulation of the Euler equations, has been developed to improve shock calculations in full-potential methods. In the Clebsch treatment of steady rotational flows, the velocity is decomposed into potential and rotational components, written in terms of scalar functions. The potential part is computed from the continuity equation using a modified version of an existing finite-volume full-potential solver; the rotational parts are determined analytically from the momentum equation based on small perturbation approximations. The solutions obtained for airfoils and wing/bodies are compared with those using the time-marching Euler methods. The agreement between the results obtained using these two approaches is good.

Design of aspirated compressor blades using three-dimensional inverse method

ABSTRACT A three-dimensional viscous inverse method is extended to allow blading design with full interaction between the prescribed pressure-loading distribution and a specified transpiration scheme. Transpiration on blade surfaces and endwalls is implemented as inflow/outflow boundary conditions, and the basic modifications to the method are outlined. This paper focuses on a discussion concerning an application of the method to the design and analysis of a supersonic rotor with aspiration. Results show that an optimum combination of pressure-loading tailoring with surface aspiration can lead to a minimization of the amount of sucked flow required for a net performance improvement at design and off-design operations. quantity is the three-dimensional blade camber surface. INTRODUCTION Turbo-compression technology has been advanced continuously by higher work capacity per stage as a result of increases in rotor speed, aerodynamic loading, and through-flow Mach numbers. With the advent of sophisticated diagnostic tools involving CFD and measurement techniques, more suitable blade shapes having relatively low losses at higher diffusion and Mach number levels have been deployed. While incremental performance advancements can be made through geometric optimization and improved design methods, severe aerodynamic limitations such as increased losses and decreased operability are often encountered when attempting to push significantly beyond current loading levels. Thus, techniques for achieving low losses with wide operability at increased aerodynamic loading levels have received renewed interest [1,2]. As shown by Loughery et al. [3], surface transpiration, properly focused, can be effective at mitigating some deleterious effects associated with increased aerodynamic loading of compressor blades. Surface transpiration is effected either through suction (i.e., aspiration) or blowing of a relatively small amount of flow along the blade or endwall surfaces. Various tactics are possible including controlling profile aerodynamics with or without shocks, managing secondary flows, and tailoring profile and endwall aerodynamic interactions. To effectively execute these schemes in an optimal sense, not only requires a good understanding of the underlying mechanisms but also availability of effective design tools. In this paper, a CFD tool that can be used to design compressor blades with surface flow transpiration is described. The proposed method is an extension of a three-dimensional inverse method reported by Dang et al. [4] and Medd [5], whereby the blade pressure loading distribution is prescribed and the derived Transpiration boundary conditions are incorporated within this framework, thereby allowing full interaction between the prescribed pressure loading distribution and the transpiration scheme. Following a brief exposition of the method, this paper focuses on a discussion concerning the aerodynamic design and performance aspects of a highly-loaded supersonic rotor with aspiration. The intent is not to develop a complete aspirated rotor design that can be manufactured and experimentally tested, but rather to showcase the utility of the inverse method. In general, aspiration is used as an add-on to improve operability of highly-loaded blades and tends to suffer from large sucked flow rate requirements and lack of a unified approach to aspirated transonic blading design. Herein, the blade design objective is an optimum combination of pressure-loading tailoring with surface aspiration resulting in a minimal amount of sucked flow for a net aerodynamic performance improvement at design and off-design operations.

Throughflow Method for Turbomachines Applicable for All Flow Regimes

A new axisymmetric throughflow method for analyzing and designing turbomachines is proposed. This method utilizes body-force terms to represent blade forces and viscous losses. The resulting equations of motion, which include these body-force terms, are casted in terms of conservative variables and are solved using a finite-volume time-stepping scheme. In the inverse mode, the swirl schedule in the bladed regions (i.e. the radius times the tangential velocity rVθ) is the primary specified flow quantity, and the corresponding blade shape is sought after. In the analysis mode, the blade geometry is specified and the flow solution is computed. The advantages of this throughflow method compared to the current family of streamline curvature and matrix methods are that the same code can be used for subsonic/transonic/supersonic throughflow velocities, and the proposed method has a shock capturing capability. This method is demonstrated for designing a supersonic throughflow fan stage and a transonic throughflow turbine stage.Copyright

Practical use of three-dimensional inverse method for compressor blade design

The practical utility of a three-dimensional inverse viscous method is demonstrated by carrying out a design modification of a first-stage rotor in an industrial compressor. In this design modification study, the goal is to improve the efficiency of the original blade while retaining its overall aerodynamic, structural, and manufacturing characteristics. By employing a simple modification to the blade pressure loading distribution (which is the prescribed flow quantity in this inverse method), the modified blade geometry is predicted to perform better than the original design over a wide range of operating points, including an improvement in choke margin.

Practical use of 3D inverse method for compressor blade design

The practical utility of a 3D inverse viscous method is demonstrated by carrying out a design modification of a first-stage rotor in an industrial compressor. In this design modification study, the goal is to improve the efficiency of the original blade while retaining its overall aerodynamic, structural and manufacturing characteristics. By employing a simple modification to the blade pressure loading distribution (which is the prescribed flow quantity in this inverse method), the modified blade geometry is predicted to perform better than the original design over a wide range of operating points, including an improvement in choke margin.Copyright