Compressor Aerodynamics

3.1.1.Compressor Aerodynamics_QRoberts, revA. ppt 关于艾滋病ppt课件精益管理ppt下载地图下载ppt可编辑假如ppt教学课件下载triz基础知识ppt HONEYWELL - CONFIDENTIAL3 Overview • 1. How does a Compressor Work? - Know your way around a compressor - Perfect and Real Diffusion Processes - Definition of Compressor Efficiency • 2. Compressor Maps and Operation - The Compressor Performance Map - Velocity Vector Diagrams and operating points • 3. Compressor Geometry and Performance - Defining Compressor geometry - Effect of Geometry on Performance • 4. Compressor Technologies - Compressor Development in Honeywell - Benchmark Compressor Concepts 3.1.1.Compressor Aerodynamics_QRoberts, revA.pptHONEYWELL - CONFIDENTIAL4 Introduction 3.1.1.Compressor Aerodynamics_QRoberts, revA.pptHONEYWELL - CONFIDENTIAL5 Overview • 1. How does a Compressor Work? - Know your way around a compressor - Perfect and Real Diffusion Processes - Definition of Compressor Efficiency • 2. Compressor Maps and Operation - The Compressor Performance Map - Velocity Vector Diagrams and operating points • 3. Compressor Geometry and Performance - Defining Compressor geometry - Effect of Geometry on Performance • 4. Compressor Technologies - Compressor Development in Honeywell - Benchmark Compressor Concepts 3.1.1.Compressor Aerodynamics_QRoberts, revA.pptHONEYWELL - CONFIDENTIAL6 What a Compressor Does Increased density allows more air to enter cylinder … Compressing the air increases its density Charge Air Cooler Exhaust Gas Engine Cylinder Fuel Flow Turbine Compressor Ambient air enters the compressor … so more fuel can be burnt … … so more engine power is produced 3.1.1.Compressor Aerodynamics_QRoberts, revA.pptHONEYWELL - CONFIDENTIAL7 Compressor Components Impeller (or Wheel) Housing Inlet Connection Discharge Connection Centre Housing Shaft Backplate Diffuser Volute 3.1.1.Compressor Aerodynamics_QRoberts, revA.pptHONEYWELL - CONFIDENTIAL8 Key Geometry Features Impeller / Wheel Shroud Inducer Exducer Volute Side (Meridional) View Vaneless Diffuser Hub Discharge Section Frontal (Axial ) View T T TT Section Tongue Full Blade Splitter Radial Clearance Axial Clearance 3.1.1.Compressor Aerodynamics_QRoberts, revA.pptHONEYWELL - CONFIDENTIAL9 How a Compressor Works (a) Increasing its velocity, (b) Increasing its temperature and pressure Air is drawn into the compressor ���� ���� ���� ���� ���� The spinning wheel passes this energy to the air by: ���� The diffuser slows the air down, converting the kinetic energy to increase the pressure further (“DIFFUSION”) ���� The volute continues to diffuse the air, collecting it and directing it to the outlet ���� Let’s look at the diffusion process in more detail Energy is provided to the compressor wheel by the turbine, via the rotating shaft ����1A ����1A 3.1.1.Compressor Aerodynamics_QRoberts, revA.pptHONEYWELL - CONFIDENTIAL10 ���� Po2 A Perfect Diffusion Process Fluid kinetic energy is converted to internal fluid energy (enthalpy) by increasing its temperature and pressure. �������� Total (stagnation) pressure Po is the pressure that is obtained by diffusing to zero velocity in the ideal process: velocity P2 pressure P1 Po1 distance Po2 = Po1 This energy can be more or less useful: the higher the pressure, the more useful it is. 3.1.1.Compressor Aerodynamics_QRoberts, revA.pptHONEYWELL - CONFIDENTIAL11 The Real Diffusion Process Some of the kinetic energy is dissipated in turbulence, or friction, which reduces the downstream pressure �������� There is a loss of total pressure during real diffusion: ���� Po1 P2 velocity pressure distance Po2 < Po1 This reduction in useful energy is related to a fluid property called ENTROPYP1 Po2 3.1.1.Compressor Aerodynamics_QRoberts, revA.pptHONEYWELL - CONFIDENTIAL12 The total (stagnation) enthalpy ho is the enthalpy obtained by diffusing to zero velocity, with no external energy transfer through heat or work: The Perfect Diffusion Process Again… �������� ���� entropy (loss) P1 ���� ����ho ����h2 h1 As the fluid diffuses, the kinetic energy is transferred to enthalpy (h). velocity pressure P2 P1 Po1 distance 1/2V1² Kinetic energy = ho- h1 ���� Po2 P2 enthalpy P2 Po2 3.1.1.Compressor Aerodynamics_QRoberts, revA.pptHONEYWELL - CONFIDENTIAL13 … And the Real Diffusion Process again P1 P2 Po2 ���� ho h2 h1 h2 and ho are the same even when loss is generated, as the total energy is the same (no heat, no work) ���� ���� However, the energy is in a less useful form: the entropy has increased entropy (loss) �������� ���� Po2 P2 P1 Po1velocity pressure distance enthalpy 3.1.1.Compressor Aerodynamics_QRoberts, revA.pptHONEYWELL - CONFIDENTIAL14 Let’s look at the whole Compressor Again ���� ���� ���� ���� ����A Entropy (Loss) Enthalpy (energy) P2 Po2 P3 Po3 P4 Po4 ho1A Po1A P1 h1 ho1 Po1 Actual pressure rises from inlet to exit…. Work transfer to fluid Shaft energy provided Air ingression Diffusion in diffuser Diffusion in volute … but total pressure falls! (due to losses) 3.1.1.Compressor Aerodynamics_QRoberts, revA.pptHONEYWELL - CONFIDENTIAL15 P1 P4 h1 P3 P2 Po1A Po2 Po3 Compressor Efficiency Enthalpy The Ideal compression achieves the required exit pressure without generating any losses The Actual compression generates some loss, which dissipates energy The Actual compression therefore needs more energy to reach the same exit pressure The Efficiency is the ratio of the Ideal to Actual energy needed to obtain the pressure ratio Actual Compression Process ∆∆∆∆hact Po,ex = Po4 Po,in = Po1 ho,in ho,ex = ho4 Compressor efficiency relates the ideal and actual processes which achieve the total pressure ratio Entropy (Loss) Ideal Compression Process ho,ideal ∆∆∆∆hideal 3.1.1.Compressor Aerodynamics_QRoberts, revA.pptHONEYWELL - CONFIDENTIAL16 Compressor Efficiency Entropy Enthalpy = Cp . T ho,in ho,ex ∆hideal ∆hact = ηηηηC (Compressor Efficiency) Cp . (To,ideal - To,in) Cp . ( To,ex - To,in)= Ideal Compression Process Po,ex Po,in (ho,ideal - ho,in) ( ho,ex - ho,in)= ∆∆∆∆hact Ideal Compression Process ho,ideal ∆∆∆∆hideal Actual Compression Process To,in [(Po,ex/Po,in) γγγγ -1/γγγγ - 1] ( To,ex - To,in) = 3.1.1.Compressor Aerodynamics_QRoberts, revA.pptHONEYWELL - CONFIDENTIAL17 Overview • 1. How does a Compressor Work? - Know your way around a compressor - Perfect and Real Diffusion Processes - Definition of Compressor Efficiency • 2. Compressor Maps and Operation - The Compressor Performance Map - Velocity Vector Diagrams and operating points • 3. Compressor Geometry and Performance - Defining Compressor geometry - Effect of Geometry on Performance • 4. Compressor Technologies - Compressor Development in Honeywell - Benchmark Compressor Concepts 3.1.1.Compressor Aerodynamics_QRoberts, revA.pptHONEYWELL - CONFIDENTIAL18 Compressor Operating Envelope limited by: Surge line Flow Stability Limit Speed/Pressure Limit Mechanical Durability “Choke” Limit Flow Capacity Limit •Standard Inlet Conditions: Metric T std -- 298 K P std -- 100 kPa M compressor (Corrected Flow Rate) P R T - T ( S t a g e T o t a l - t o - T o t a l P r e s s u r e R a t i o ) Constant Speed Lines Iso-Efficiency Islands The Compressor Performance Map 3.1.1.Compressor Aerodynamics_QRoberts, revA.pptHONEYWELL - CONFIDENTIAL19 ηc = m.Cp.∆Tideal m.Cp.∆Tactual Nc*= Nc √T1c(K)/298 Wc*= m(kg/s)√(T1c(K)/298) P1c(kPa)/100 pic= P2c tot P1c tot Compressor Map, Honeywell Style ηc, Wc*and Nc* formulae are also given at the bottom of the map 3.1.1.Compressor Aerodynamics_QRoberts, revA.pptHONEYWELL - CONFIDENTIAL20 Compressor Operation along a Speedline M compressor (Corrected Flow Rate) P R T - T ( S t a g e T o t a l - t o - T o t a l P r e s s u r e R a t i o ) Let’s look inside the compressor as we move along a constant speed line. A = design point B = choke C = stall D = surge A B CD There are four distinct operating régimes to be explored: First, let’s look at the velocities inside the compressor wheel, to learn more about how a compressor works 3.1.1.Compressor Aerodynamics_QRoberts, revA.pptHONEYWELL - CONFIDENTIAL21 Velocity Vector Diagram Unless there are inlet guide vanes, inlet velocity is purely axial U = Blade velocity W = Relative Air velocity V = Absolute Air velocity x, axial direction r, radial direction s, streamwise direction ΩΩΩΩ V1x V2r V2 W2 V2r V2θθθθ U2 U2 = ΩΩΩΩ R2 V2 W2 V2r V2θθθθ θ, θ, θ, θ, tangential direction s, streamwise direction U1 = ΩΩΩΩ R1W1 V1 U1 = ΩΩΩΩ R1 W1 V1 W = V - U ___ 3.1.1.Compressor Aerodynamics_QRoberts, revA.pptHONEYWELL - CONFIDENTIAL22 A2 Vector Diagram and Energy Transfer U2 > U1 (radius increases) W2 < W1 (flow area & density increases) ���� V2 >> V1 (kinetic energy given to air) Now we’re ready to look at the four operating régimes V1 U1 = ΩΩΩΩ R1 W1 U2 = ΩΩΩΩ R2 V2 W2 V2r V2θθθθ θ, θ, θ, θ, tangential direction s, streamwise direction A1 R1 R2 ( )θRVmTorque &∆= ( )θUVm∆= & Ω⋅= TorquepowerShaft θ22VUmH o && =∆���� no inlet swirl � V1θ = 0 ( )θRVmPower Ω∆= &���� The Euler Turbomachinery Equation relates shaft power to velocity diagram : ΩΩΩΩ 3.1.1.Compressor Aerodynamics_QRoberts, revA.pptHONEYWELL - CONFIDENTIAL23 A : Design Point (Peak Efficiency) Inlet flow is well matched to blade leading edge Air velocity increases smoothly in wheel U1 W1 V1 U2 V2 W2 V2r V2θθθθ V2 >> V1, as shown before Abs Mach n° 3.1.1.Compressor Aerodynamics_QRoberts, revA.pptHONEYWELL - CONFIDENTIAL24 B : Choke Point (Max Flow) U2 V2 W2 V2r V2θθθθ Abs Mach n° Higher flow increases the inlet axial velocity and reduces inlet static pressure Low exit pressure �low density and high exit relative velocity Lower V2θθθθ ����less Euler work ����lower pressure ratio Large velocities at shroud and in diffuser ����low efficiency U1W1 V1 3.1.1.Compressor Aerodynamics_QRoberts, revA.pptHONEYWELL - CONFIDENTIAL25 C : Stall (Reduced Flow) U2 V2 W2 V2r V2θθθθ U1 W1 V1 Reversed flow along shroud ����low efficiency and instability Lower flow and higher density �low exit relative velocity Higher V2θθθθ ����more Euler work ����higher pressure ratio Flow separates in wheel inducer ����loss and flow instability Lower flow reduces inlet axial velocity �flow angle ill- matched to blade Abs Mach n° 3.1.1.Compressor Aerodynamics_QRoberts, revA.pptHONEYWELL - CONFIDENTIAL26 C : Stall Instabilities • Stall starts to occur just to the left of the max efficiency point on the compressor map • It usually starts in a single blade row, apparently at random • As mass flow continues to fall, the separation increases in size • Eventually, the flow in adjacent blade rows is affected, and the stall moves around the compressor inlet: Rotating stall 3.1.1.Compressor Aerodynamics_QRoberts, revA.pptHONEYWELL - CONFIDENTIAL27 D : Surge (Unstable flow) • As the mass flow continues to fall, the stall becomes so severe that the airflow in the compressor breaks down completely • This allows high-pressure air from the downstream ducting to rush back through the compressor • Once the air in the downstream piping is depleted, the backflow ends and the flow in the compressor is able to re-establish itself • Once the downstream piping fills up again, the surge cycle repeats itself. Pressure ratio surge point peak efficiency Mass flow rate0 +- 3.1.1.Compressor Aerodynamics_QRoberts, revA.pptHONEYWELL - CONFIDENTIAL28 D : Surge (continued) • The onset, strength and frequency of the surge depend upon the design of the engine inlet system - in particular, the length and volume of the downstream piping • On a gas-stand, there is usually more pipework downstream of the compressor than on a normal engine • Surge on the gas-stand therefore usually occurs at higher mass flows than on an engine. • HOWEVER: if the compressor is only feeding two engine cylinders, the pulsating airflow requirement can trigger early surge in the compressor • At pressure ratios above 2:1, compressor surge is very damaging to the engine and turbocharger, and must be avoided Pressure Ratio mass flow rate0 +- small downstream piping (engine) large downstream piping (gas-stand) 3.1.1.Compressor Aerodynamics_QRoberts, revA.pptHONEYWELL - CONFIDENTIAL29 Efficiency Breakdown in Compressor 64% 78% 59% 5% 11% 8% 7%8% 5% 6% 20% 10% 17% 1% 2% 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% SURGE DESIGN CHOKE Operating Point E f f i c i e n c y Wheel Diffuser Volute Discharge NET Compressor Stage Losses • Losses in the compressor stage depend on the operating point • In general, ~50% of efficiency drop occurs in the wheel • Losses in the volute+discharge are more significant at choke: - higher swirl velocities - less overall compressor work 3.1.1.Compressor Aerodynamics_QRoberts, revA.pptHONEYWELL - CONFIDENTIAL30 Overview • 1. How does a Compressor Work? - Know your way around a compressor - Perfect and Real Diffusion Processes - Definition of Compressor Efficiency • 2. Compressor Maps and Operation - The Compressor Performance Map - Velocity Vector Diagrams and operating points • 3. Compressor Geometry and Performance - Defining Compressor geometry - Effect of Geometry on Performance • 4. Compressor Technologies - Compressor Development in Honeywell - Benchmark Compressor Concepts 3.1.1.Compressor Aerodynamics_QRoberts, revA.pptHONEYWELL - CONFIDENTIAL31 Compressor Geometry Parameters: • Wheel: TRIM – Inducer area function EI – Exit Area / Inlet Area •Diffuser: DE – Exit Area / Inlet Area •Housing A/R – Housing Size function Compressor 1D Geometry Parameters φ d1s φ d2 φ d1h φ d3 b3 δ2 b2 + RTT Area ATT 33 d2(b2+δ2) bd DE = 100 x pi pi )( 21214 22 hs dd bd EI = 100 x − pi pi d1s2TRIM = d22 100 x ATTA/R = RTT (inch) TT section 3.1.1.Compressor Aerodynamics_QRoberts, revA.pptHONEYWELL - CONFIDENTIAL32 • Wheel Trim - Used to modify the maximum flow of the compressor - First “lever” when matching compressor map to target - High trim is best for flow range at low PR*; low trim at high PR • EI - Controls flow width and peak efficiency - High EI is generally better for low PR applications - High EI is generally good for efficiency, bad for stability • DE - Similar effect to EI - DE is optimized to find best trade-off between efficiency and flow range • A/R - Describes size of compressor housing - Affects efficiency and surge line, only slight effect on max flow How do they change the map? * PR = pressure ratio 3.1.1.Compressor Aerodynamics_QRoberts, revA.pptHONEYWELL - CONFIDENTIAL33 Wheel Backsweep Low Backsweep (ββββ2): - high Euler work V2θθθθ= high PR - high exit angle αααα2 = low stability, poor flow range Low backsweep wheels are usual in commercial vehicle applications, where high PRs are needed V2 W2 V2θθθθU2 ββββ2 αααα2 V2θθθθ V2W2 U2 ββββ2 αααα2 High Backsweep (ββββ2): - low Euler work V2θθθθ= low PR - low exit angle αααα2 = good stability, good flow range High backsweep wheels are primarily used in PV due to high flow range requirements 3.1.1.Compressor Aerodynamics_QRoberts, revA.pptHONEYWELL - CONFIDENTIAL34 “How can I improve my Compressor Performance?” • Choose the appropriate compressor wheel design from the available options • Official (product plan) compressor maps should be readily available • Generally, use high backsweep wheels for wide flow (gasoline, VNT) and low backsweep wheels for high pressure ratio applications • Ask the local aero or experienced application engineer for advice 1 1.5 2 2.5 3 3.5 4 4.5 5 0 20 40 60 80 100 120 Corrected Air Flow (lbs/min) P r e s s u r e R a t i o ( t / t ) P 2 c / P 1 c BCI5(108) 48trim 0.86 A/R BCI32(108) 50trim 1.01 A/R C117(108) 50trim 0.86 A/R 3.1.1.Compressor Aerodynamics_QRoberts, revA.pptHONEYWELL - CONFIDENTIAL35 “How can I improve my Compressor Performance?” • Search among the available maps for the best geometry parameters (trim, A/R, EI, DE) • The best-performing maps are usually selected from all the options and chosen as Product Plan maps. • This gives finer control to suit the required flow range and efficiency • If no option is perfect, remember that the gas-stand surge line is usually conservative 1 1.5 2 2.5 3 3.5 4 4.5 0 20 40 60 80 100 Corrected Air Flow (lbs/min) P r e s s u r e R a t i o ( t / t ) P 2 c / P 1 c 3.1.1.Compressor Aerodynamics_QRoberts, revA.pptHONEYWELL - CONFIDENTIAL36 “How can I improve my Compressor Performance?” • When packaging the compressor housing, make sure to avoid tight bends in the ducts - This is especially important just upstream of the compressor inlet � Can reduce wheel flow capacity, and trigger early surge - Sharp bends downstream of the TT section can also reduce surge margin and efficiency • Keep flow changes as gradual as possible in all pipes - Never reduce the pipe flow area after the discharge - Keep pipe wall divergent half-angles (αααα) below 5° • Always discuss severe packaging contraints with an aero specialist L A1 A2 X !! ( ) L AA pipiα 12 44 2tan − = 3.1.1.Compressor Aerodynamics_QRoberts, revA.pptHONEYWELL - CONFIDENTIAL37 Overview • 1. How does a Compressor Work? - Know your way around a compressor - Perfect and Real Diffusion Processes - Definition of Compressor Efficiency • 2. Compressor Maps and Operation - The Compressor Performance Map - Velocity Vector Diagrams and operating points • 3. Compressor Geometry and Performance - Defining Compressor geometry - Effect of Geometry on Performance • 4. Alternative Compressor Technologies - Compressor Development in Honeywell - Benchmark Compressor Concepts 3.1.1.Compressor Aerodynamics_QRoberts, revA.pptHONEYWELL - CONFIDENTIAL38 Alternative Compressor Technologies • Most of the compressors produced by HTT are of the single- stage, vaneless diffuser type described above • However, alternative concepts exist in HTT and elsewhere: - Ported shroud housings - Vaned diffusers - Variable geometry compressors - Two-stage, one-shaft - Vaned ported shroud – benchmark from IHI - Casing treatment – benchmark from Holset • These are described in brief in the following slides 3.1.1.Compressor Aerodynamics_QRoberts, revA.pptHONEYWELL - CONFIDENTIAL39 Ported Shroud Housings Incoming air flow wheel housing Supporting ribs Port inlet Incoming air flow wheel housing Supporting ribs Port inlet • What is it? - Cavity above the inducer - Connected to main blade passage by a small annular slot (port) - Supported by ribs (usually four) • What does it do? - Improves the flow range of the compressor map - Often with a small efficiency penalty • How does it work? - At choke, allows flow to bypass wheel throat and pass directly into wheel - At surge, allows separated and unstable flow to pass out of wheel and back into inlet, thereby stabilizing the flow • Anything else I should know? - The spinning blade pressure field interacts with the stationary struts, which generates unwanted noise - Noise limits the use of ported shroud housings in the PV market - Ported shroud is considered standard for CV applications as noise is less of an issue 3.1.1.Compressor Aerodynamics_QRoberts, revA.pptHONEYWELL - CONFIDENTIAL45 Summary • The compressor converts shaft power to kinetic energy in the